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Huixin Liu Last modified date:2018.07.28

Associate Professor / Meteorology & Solar-Terrestrial physics Laboratory
Department of Earth and Planetary Sciences
Faculty of Sciences


Graduate School
電磁学
Undergraduate School
基幹教育セミナー
Other Organization
Administration Post
Other
Other


Phone
092-802-4234
Fax
092-802-4208
Academic Degree
Doctor of Science
Country of degree conferring institution (Overseas)
Yes
Field of Specialization
Space Physics, ionosphere-thermosphere-lower atmosphere coupling, atmospheric dynamics
ORCID(Open Researcher and Contributor ID)
0000-0001-7073-4366
Total Priod of education and research career in the foreign country
08years00months
Outline Activities
1. Research: Vertical coupling in the Earth's atmosphere
Vertical coupling in the Earth’s atmosphere from the ground surface to the topside (1000 km), in terms of both neutral-neutral and plasma-neutral interaction, is an essential aspect for the Sun-Earth connection. It holds the key to further advance the current climate and weather predictions. On this solar-terrestrial chain, the thermosphere is a critical region in linking the lower and upper atmosphere. Dr. Liu's research focuses on the thermosphere and its dynamic and chemical coupling to other atmospheric regions. Such research functions as a natural catalyst for spurring multi-disciplinary research activities, which enable us to cross the science boundaries between meteorology and space science in particular, between physics and chemistry in general. Thus, by enhancing the scientific and educational contacts, it will help to strengthen the ties among various divisions in the Faculty of Science and foster mutual improvements. Current and past topics:
-Ion-neutral interaction in the thermosphere and ionosphere: equatorial mass density anomaly and wind jets
- The thermosphere/ionosphere longitudinal variation: Wave-4 structure and coupling with lower atmosphere
- How does the thermosphere respond to Stratosphere sudden warmings?
- How does El Nino Southern Oscillation (ENSO) affect MLT region tidal activity?
- Modelling global warming effect on the upper atmosphere
2. Education
Teach atmospheric physics and plasma physics course to both undergraduate and graduate students. Depends on students' level, some courses are taught in English, and some are in Japanese.
3. Social activity:
- Panel reviewer for national science foundations and space agencies (NSF (US), NASA (US), Canadian NSF, JSPS, etc.)
- Editor for science journals: Space Weather (AGU 2018~), Ann. Geophyicae (EGU 2017~), Earth, Planets and Space (SGEPSS 2016~)
- Convener at international meetings like AGU (american geophysical union), AOGS, and JpGU.
- Science program chair for joint JpGU-AGU meeting in 2017.
- SGEPSS's Mesosphere-thermosphere-ionosphere (MTI) working group organizer (2009~2013)
- SGEPSS member, AGU member, EGS member
- Frequent reviewer of JGR, GRL, Ann. Geo, Science
Research
Research Interests
  • Response of the upper atmosphere to El Nino Southern Oscillation (ENSO)
    keyword : vertical coupling, thermosphere, ionosphere, troposphere, ENSO
    2018.04~2021.03.
  • ENSO effect on the upper atmosphere: the role of O3
    keyword : vertical coupling, thermosphere, ionosphere, troposphere, ENSO, Ozone layer
    2018.04~2022.03.
  • Exploring the role of gravity waves in seeding equatorial plasma bubbles
    keyword : thermosphere, ionosphere, atmospheric gravity waves, ionospheric irregularities, equatorial plasma bubble
    2018.04~2020.03.
  • Response of the upper atmosphere to El Nino Southern Oscillation (ENSO)
    keyword : vertical coupling, thermosphere, ionosphere, troposphere, ENSO
    2015.04~2018.03.
  • Ionospheric Current system observed by the CHAMP satellite
    keyword : thermosphere, ionosphere, ionospheric current system
    2012.04~2015.03.
  • Response of the upper atmosphere to stratosphere sudden warming
    keyword : vertical coupling, thermosphere, ionosphere, stratosphere
    2012.01~2014.08.
  • Coupling of the Earth's atmospheric layers: interactions between the
    ionosphere, thermosphere and mesosphere in the Sun-Earth system
    keyword : vertical coupling, thermosphere, ionosphere,
    2009.04~2012.03.
Academic Activities
Books
1. Hermann Lühr, Huixin Liu, Jeahueng Park, and Sevim Müller, Aeronomy of the Earth's Atmosphere and Ionosphere: New aspects of the coupling between thermosphere and ionosphere, with special regards to CHAMP mission results, Springer, 303-316, 2011.08.
2. Claudia Stolle, Huixin Liu, Modeling the Ionosphere-Thermosphere System: Chapter 21:Low-latitude ionosphere and thermosphere: decadal observations from the CHAMP mission, Americal Geophysical Union, doi:10.1002/9781118704417.ch21, 2014.08.
3. Huixin Liu, Hermann Lühr, W. Koehler, Earth Observation with CHAMP, Springer, Berlin, 2004.12.
Reports
1. Huixin Liu, J. Thayer, Y. Zhang, W. Lee, The non-storm time corrugated upper thermosphere: What's beyond MSIS?, Space Weather, 10.1002/2017SW001618, 2017.06.
2. Claudia Stolle, Huixin Liu, CHAMP observations of the low latitude ionosphere and thermosphere and comparisons to physical models, AGU monograph: Modeling the Ionosphere-Thermosphere, 2014.02, [URL], During its more than 10~years mission the CHAMP (CHAllenging
Minisatellite Payload) satellite has revealed exciting and new
observations of the upper F~region ionosphere and the thermosphere.
Special benifit has been gained from simultaneous observations of plasma
and neutrals, and the magnetic field, which has led to many new findings and insight in the thermosphere-ionosphere system.
This chapter reviews those new findings at low and equatorial latitudes,
from the point of view of coupling between different atmospheric regions.
On specific examples it is demonstrated that results of physical models have large impact in understanding new observations and related generation processes. However, further model development is still required to fully reproduce even large scale ionospheric and thermospheric features. .
Papers
1. 1. R. Shi, B. Ni, D. Summers, Huixin Liu, Y. Yoshikawa, B. Zhang, Generation of electron acoustic waves in the topside ionosphere from coupling with kinetic Alfven waves: a new electron energization mechanism, Geophysical Research Letters, 10.1002/2018GL077898, 45, 14, 2018.05.
2. Huixin Liu, Nicholas Pedatella, Klemens Hocke, Medium-scale gravity wave activity in the bottomside F region in tropical regions, Geophysical Research Letters, 10.1002/2017GL073855, 44, 14, 7099-7105, 2017.07, Thermospheric gravity waves (GWs) in the bottomside F region have been proposed to play a key role in the generation of equatorial plasma bubbles (EPBs). However, direct observations of such waves are scarce. This study provides a systematic survey of medium-scale (<620 km) neutral atmosphere perturbations at this critical altitude in the tropics, using 4 years of in situ Gravity Field and Steady-State Ocean Circulation Explorer satellite measurements of thermospheric density and zonal wind. The analysis reveals pronounced features on their global distribution and seasonal variability: (1) A prominent three-peak longitudinal structure exists in all seasons, with stronger perturbations over continents than over oceans. (2) Their seasonal variation consists of a primary semiannual oscillations (SAO) and a secondary annual oscillation (AO). The SAO component maximizes around solstices and minimizes around equinoxes, while the AO component maximizes around June solstice. These GW features resemble those of EPBs in spatial distribution but show opposite trend in climatological variations. This may imply that stronger medium-scale GW activity does not always lead to more EPBs. Possible origins of the bottomside GWs are discussed, among which tropical deep convection appears to be most plausible..
3. Huixin Liu, Jeff Thayer, Yongliang Zhang, Woo Kyoung Lee, The non–storm time corrugated upper thermosphere
What is beyond MSIS?, Space Weather, 10.1002/2017SW001618, 15, 6, 746-760, 2017.06, Observations in the recent decade have revealed many thermospheric density corrugations/perturbations under nonstorm conditions (Kp < 2). They are generally not captured by empirical models like Mass Spectrometer Incoherent Scatter (MSIS) but are operationally important for long-term orbital evolution of Low Earth Orbiting satellites and theoretically for coupling processes in the atmosphere-ionosphere system. We review these density corrugations by classifying them into three types which are driven respectively by the lower atmosphere, ionosphere, and solar wind/magnetosphere. Model capabilities in capturing these features are discussed. A summary table of these corrugations is included to provide a quick guide on their magnitudes, occurring latitude, local time, and season..
4. Delores Knipp, Huixin Liu, Hisashi Hayakawa, Ms. Hisako Koyama:From Amateur Astronomer to Long-Term Solar Observer, Space Weather, 10.1002/2017SW001704, 15, 10, 1215-1221, 2017.10, The path to science for a girl of any nationality born in the early twentieth century was formidable-to-nonexistent. Yet paths were forged by a few. We present the little-known story of one of Japan's premier solar observers and her contribution to the world's understanding of sunspots and space weather cycles. Ms. Hisako Koyama, born in Tokyo in 1916, became a passionate amateur astronomer, a dedicated solar observer, and a long-serving staff member of the National Museum of Nature and Science, Tokyo. As a writer for amateur astronomy journals she advised many on the details and joys of sky viewing. She created a consistent, extended record of sunspots. Her multidecade archive of sunspot drawings is one of the “backbones” for the recent international recalibration of the sunspot record that provides insight into space weather reaching back to the early 1600s. We detail her contributions to the citizens of Japan as an ambassador of astronomy and her international contribution to understanding the symmetries and asymmetries of the solar cycle. We comment on the value of her continuous record of sunspots and on her tenacity in promoting a science that links to space weather..
5. N. S.A. Hamid, Huixin Liu, T. Uozumi, Akimasa Yoshikawa, N. M.N. Annadurai, Peak time of equatorial electrojet from different longitude sectors during fall solar minimum, Journal of Physics: Conference Series, 10.1088/1742-6596/852/1/012015, 852, 1, 2017.06, Equatorial electrojet is an eastward flowing current at about ±3° dip equator. This current intensity is always higher during noontime as it is greatly influenced by the ionization of Earth ionosphere. Apart from that, previous study had shown that EEJ current varies with longitude and latitude as well as solar cycle. The aim of this study is to investigate the peak time of EEJ current at different longitude sectors using simultaneous data in 2009. By eliminating Sq current contribution and normalizing ground-based data from MAGDAS/CPMN, IIG and WDC network, we managed to reach our purpose and gain reliable output. We found out that EEJ is strongest in South American sector. Our results show that the peak EEJ during fall solar minimum is observed at 11 LT for South American, Indian and Southeast Asian sector but it is 1 hr earlier in African sector..
6. Liu Huixin, Y. Sun, Yasunobu Miyoshi, H. Jin, ENSO effects on MLT diurnal tides: A 21 year reanalysis data-driven GAIA model simulation, J. Geophys. Res, 10.1002/2017JA024011, 122, 2017.05, Tidal responses to El Niño–Southern Oscillation (ENSO) in the mesosphere and lower thermosphere (MLT) are investigated for the first time using reanalysis data-driven simulations covering
21 years. The simulation is carried out with the Ground-to-topside Atmosphere-Ionosphere model for Aeronomy (GAIA) during 1996–2016, which covers nine ENSO events. ENSO impacts on diurnal tides at 100 km altitude are analyzed and cross-compared among temperature (T), zonal wind (U), and meridional wind (V), which reveals the following salient features: (1) Tidal response can differ significantly among T,
U, and V in terms of magnitude and latitudinal structure, making detection of ENSO effects sensitive to
the parameter used and the location of a ground station; (2) the nonmigrating DE3 tide in T and U shows
a prominent hemisphere asymmetric response to La Niña, with an increase between 0∘ and 30∘N and a decrease between 30∘ and 0∘S. In contrast, DE3 in V exhibits no significant response; (3) the migrating DW1 enhances during El Niño in equatorial regions for T and U but in off-equatorial regions for V. As the first ENSO study based on reanalysis-driven simulations, GAIA’s full set of tidal responses in T, U, and V provides us with a necessary global context to better understand and cross-compare observations during
ENSO events. Comparisons with observations during the 1997–98 El Niño and 2010–11 La Niña reveal good agreement in both magnitude and timing. Comparisons with “free-run” WACCM simulations (T) show consistent results in nonmigrating tides DE2 and DE3 but differences in the migrating DW1 tide..
7. L. Liu, Liu Huixin, H. Le, Y. Chen, Y. Sun, B. Ning, L. Hu, W. Wan, N. Li, J. Xiong, Mesospheric temperatures estimated from the meteor radar observations at Mohe, China, J. Geophys. Res, 10.1002/2016JA023776, 122, 2017.03.
8. Y. Yamazaki, Liu Huixin, Y. Sun, Yasunobu Miyoshi, M. Kosch, M. Mlynczak, Quasi-biennial oscillation of the ionospheric wind dynamo, J. Geophys. Res, 10.1002/2016JA023684, 122, 2017.03.
9. L. Liu, Liu Huixin, Y. Chen, H. Le, Y. Sun, B. Ning, L. Hu, W. Wan, Variations of the meteor echo heights at Beijing and Mohe, J. Geophys. Res, 10.1002/ 2016JA023448, 122, 2017.01.
10. J. Guo, F. Wei, X. Feng, J. Forbes, Y. Wang, Liu Huixin, W. Wan, Prolonged multiple excitation of large-scale traveling atmospheric disturbances (TADs) by successive and interacting coronal mass ejections, J. Geophys. Res, 10.1002/2015JA022076, 2016.07.
11. Liu Huixin, E. Doornbos, J. Nakashima, Thermospheric wind observed by GOCE: wind jets and seasonal variations, J. Geophys. Res, 10.1002/2016JA022938, 121, 2016.06.
12. Jianpeng Guo, F. Wei, Xueshang Feng, Liu Huixin, Weixing Wan, et. al, Alfvén waves as a solar-interplanetary driver of the thermospheric disturbances, Scientific Reports, 10.1038/srep-18895, 2016.05.
13. Liu Huixin, Thermospheric inter-annual variability and its potential connection to ENSO and stratospheric QBO, Earth. Planets and Space, 10.1186/s40623-016-0455-8, 2016.04.
14. Jianpeng Guo, J. Forbes, F. Wei, Xueshang Feng, Liu Huixin, Weixing Wan, et. al, Observations of a large-scale gravity wave propagating over an extremely large horizontal distance in the thermosphere, Geophys. Res. Lett., 10.1002/2015GL065671, 42, 2015.08.
15. Nurul Shazana Abdul Hamid, Huixin Liu, Teiji Uozumi, Kiyohumi Yumoto, Empirical model of equatorial electrojet based on ground-based magnetometer data during solar minimum in fall, Earth. Planets and Space, 10.1186/s40623-015-0373-1, 67, 2015.06.
16. Nurul Shazana Abdul Hamid, Huixin Liu, Teiji Uozumi, Kiyohumi Yumoto, Longitudinal and Solar Activity Dependence of Equatorial Electrojet At Southeast Asian Sector, IEEE, 262-266, 2015.06.
17. L. Chang, Liu Huixin, Yasunobu Miyoshi, C. Chen, F. Chang, C. Lin, J. Y. Liu, Y. Y. Sun, Structure and origins of the Weddell Sea Anomaly from tidal and planetary wave signatures in FORMOSAT-3/COSMIC observations and GAIA GCM simulations, J. Geophys. Res., doi:10.1002/2014JA020752, 120, 1325-1340, 2015.02, The Weddell Sea Anomaly (WSA) is a recurrent feature of the austral summer midlatitude ionosphere where electron densities are observed to maximize during the local nighttime. In this study, tidal decomposition is applied to FORMOSAT-3 (Formosa Satellite)/Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) total electron content (TEC) and electron density observations between 2007 and 2012 to quantify the components dominating local time and spatial variation in the WSA region. Our results present some of the first three-dimensional spaceborne analyses of the WSA from a tidal perspective over multiple years. We find that the features of the WSA can be reconstructed as the result of superposition between the dominant diurnal standing (D0), eastward wave number 1 (DE1), westward wave number 2 (DW2), and stationary planetary wave 1 (SPW1) components in TECs, producing the characteristic midnight WSA peak. The D0, DE1, DW2, and SPW1 components are found to be an interannually recurring feature of the southern midlatitude to high-latitude ionosphere during the summer, manifesting as enhancements in electron density around 300 km altitude of the summer middle to high magnetic latitudes. The phases of the aforementioned nonmigrating diurnal signatures in electron density in this region are near evanescent, suggesting in situ generation, rather than upward propagation from below. However, the SPW1 signature shows some signs of an eastward tilt with altitude, suggesting possible downward propagation. The relation of these components to possible generation via in situ photoionization or plasma transport along magnetic field lines is also discussed using results from the Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy (GAIA) general circulation model (GCM), connecting the tidal interpretation of the WSA to previously examined generation mechanisms..
18. K.-I. Oyama, J. T. Jhou, J. T. Lin, C. Lin, Liu Huixin, Kiyohumi Yumoto, Ionospheric response to 2009 Sudden Stratospheric Warming in the northern hemisphere, J. Geophys. Res., 10.1002/2014JA020014, 119, 1-16, 2014.11, Abstract We study the behavior of the F region ionosphere in the Northern Hemisphere during the sudden stratospheric warming period of 19–30 January 2009 by using FORMOSAT-3/Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) ionosphere data (NmF2, hmF2, and height profile). We concentrated our study in the longitude bands 30°E–30°W, as well as 150°E–150°W, where no detailed study has been reported so far. At low magnetic latitude, the NmF2 decreases except during 09–12 LT: in the latitude zone of 20–40° NmF2 shows an increase of 30% during 09–12 LT. At higher magnetic latitude the NmF2 shows an increase during daytime and a reduction in the evening (21–03 LT). There is a latitude zone where NmF2 does not change. The latitude seems to correspond to the latitude where atmospheric temperature does not change. The behavior of the NmF2 seems to suggest a reduction of neutral density in low latitude and increase of neutral density in higher latitude. During the period of day of year (DOY) 25–31, the NmF2 shows a drastic reduction only during 06–09 LT in low latitudes, which is slightly away from geomagnetic equator. This special feature which occurred during declining phase of the sudden stratospheric warming (SSW) might be explained as due to enhanced dynamo electric field. The study suggests global change of the thermosphere including dynamo region, in spite of the fact that SSW is a high-latitude phenomenon which occurred much below the height region of thermosphere..
19. Nurul Shazana Abdul Hamid, Huixin Liu, Teiji Uozumi, Kiyohumi Yumoto, Relationship between equatorial electrojet and global Sq currents at dip equator region, Earth, Planets and Space, http://www.earth-planets-space.com/content/66/1/146, 66, 1-11, 2014.10, The equatorial electrojet (EEJ) is a strong eastward ionospheric current flowing in a narrow band along the dip equator. In this study, we examined the EEJ-Sq relationship by using observations at six stations in the South American, Indian, and Southeast Asian sectors. The analysis was carried out with data on geomagnetically quiet days with Kp ≤3 from 2005 to 2011. A normalization approach was used because it yields more accurate results by overcoming the uncertainties due to latitudinal variation of the EEJ and Sq. A weak positive correlation between the EEJ and Sq was obtained in the Southeast Asian sector, while weak negative correlations were obtained in the South American and Indian sectors. EEJ-Sq relationship is found to be independent of the hemispheric configuration of stations used to calculate their magnetic perturbations, and it also only changed slightly during low and moderate solar activity levels. These results demonstrate that the Southeast Asian sector is indeed different from the Indian and South American sectors, which is indicative of unique physical processes particularly related to the electro-dynamo. Furthermore, we also demonstrate that the definition of the EEJ, that is, the total current or enhanced current, can significantly affect the conclusions drawn from EEJ-Sq correlations..
20. C. Lin, J. T. Lin, C.H. Chen, J. Y. Liu, Y. Y. Sun, Y. Kakinam, M. Matsumura, Liu Huixin, R. J. Rau, Ionospheric shock waves triggered by rockets, Ann. Geophys., 10.5194/angeo-32-1145-2014, 32, 1145-1152, 2014.09, This paper presents a two-dimensional structure of the shock wave signatures in ionospheric electron den- sity resulting from a rocket transit using the rate of change of the total electron content (TEC) derived from ground- based GPS receivers around Japan and Taiwan for the first time. From the TEC maps constructed for the 2009 North Korea (NK) Taepodong-2 and 2013 South Korea (SK) Ko- rea Space Launch Vehicle-II (KSLV-II) rocket launches, fea- tures of the V-shaped shock wave fronts in TEC perturba- tions are prominently seen. These fronts, with periods of 100–600s, produced by the propulsive blasts of the rock- ets appear immediately and then propagate perpendicularly outward from the rocket trajectory with supersonic velocities between 800–1200 m s−1 for both events. Additionally, clear rocket exhaust depletions of TECs are seen along the tra- jectory and are deflected by the background thermospheric neutral wind. Twenty minutes after the rocket transits, de- layed electron density perturbation waves propagating along the bow wave direction appear with phase velocities of 800– 1200 m s−1. According to their propagation character, these delayed waves may be generated by rocket exhaust plumes at earlier rocket locations at lower altitudes..
21. Jianpeng Guo, Liu Huixin, Xueshang Feng, Weixing Wan, Yue Deng, Chaoxu Liu, Constructive interference of large-scale gravity waves excited by interplanetary shock on 29 October 2003: CHAMP observation, J. Geophys. Res., 10.1002/2014JA020255, 119, 1-6, 2014.08, In this paper we report the detection of full constructive interference between two large-scale
gravity waves in the upper thermosphere from the CHAMP accelerometer measurements. The two waves
are separately excited in northern and southern auroral regions by the shock-induced auroral intensification
on 29 October 2003. They propagate equatorward and encounter near the equator, where constructive
interference occurs and causes nightside equatorial neutral density enhancements of ∼60%. This result
demonstrates that the constructive interference can be a potential mechanism for large density increases in
the equatorial region during magnetically active periods..
22. Liu Huixin, Yasunobu Miyoshi, Saburo Miyahara, H. Jin, H. Fujiwara, H. Shinagawa, Thermal and dynamical changes of the zonal mean state of the thermosphere during the 2009 SSW: GAIA simulations, J. Geophys. Res., 10.1002/2014JA020222, 119, 1-7, 2014.08, Changes of the zonal mean state of the thermosphere during the 2009 stratospheric sudden warming (SSW) have been investigated using the GAIA model. Both the zonal mean thermal and dynamical structure of the thermosphere exhibit pronounced changes during the SSW in terms of zonal mean temperature and winds. First, the zonal mean temperature above 100 km altitude drops at all latitudes except for in a narrow band around $60^\circ$N. Such temperature perturbations are found to be dominantly caused by changes in direct heating/cooling processes related to solar radiation and thermal heat conduction at high latitudes, but by dynamical processes in tropical regions. Second, the zonal mean zonal wind experiences a strong westward perturbation in the tropical thermosphere, along with distinct change in the meridional circulation. This change consists of two parts. One is a global scale north-to-south flow accompanied with upwelling/downwelling in the northern/southern polar region, the other is a fountain-like flow in tropical lower thermosphere. The large enhancement of semi-diurnal tides is suggested to be the primary cause for the fountain-like flow..
23. Jianpeng Guo, Liu Huixin, Xueshang Feng, T. I. Pulkkinen, E. I. Tanskanen, Chaoxu Liu, Dingkun Zhong, Yuan Wang, MLT and seasonal dependence of auroral electrojets: IMAGE magnetometer network observations, J. Geophys. Res., 10.1002/2014JA019843, 119, ?-?, 2014.04, Total eastward and westward electrojet currents (EEJ and WEJ) and their central latitudes derived from the International Monitor for Auroral Geomagnetic Effects (IMAGE) network magnetic measurements are analyzed for the combined MLT (magnetic local time) and seasonal dependence during the period 1995–2009. EEJ shows a strong MLT variation with significant dependence on season. During summer months the maxima occur around 1600–1800 MLT, whereas during winter months the maxima occur around 1800–2000 MLT. Moreover, the summer maxima are much larger than the winter maxima and appear at higher latitudes. The summer maxima are mainly associated with the solar EUV conductivity effect, while the winter maxima are mainly due to the contribution of northward convective electric field. EEJ exhibits a dominant annual variation with maximum in summer and minimum in winter. WEJ also exhibits a strong MLT variation with significant dependence on season. The maxima occur around 0200–0400 MLT during summer months, around 0000–0200 MLT during winter months, and around 0000–0400 MLT during equinoctial months. Moreover, the equinoctial maxima are much larger than the summer and winter maxima and appear at relatively lower latitudes. The seasonal variations in WEJ are the combinations
of annual variations and semiannual variations. Both annual and semiannual variations show significant dependence on MLT. These results increase our knowledge on what factors contribute to the auroral electrojets as well as their magnetic signatures and hence help us better understand the limitations of global auroral electrojet indices, such as the AE and SME indices..
24. Jianpeng Guo, T. I. Pulkkinen, E. I. Tanskanen, Xueshang Feng, Barbara A. Emery, Liu Huixin, Chaoxu Liu, Dingkun Zhong, Annual variations in westward auroral electrojet and substorm occurrence rate during solar cycle 23, J. Geophys. Res., 10.1002/2013JA019742, 119, ?-?, 2014.03, The International Monitor for Auroral Geomagnetic Effects network magnetic measurements during the period 1995–2009 are used to characterize the annual variations in the westward electrojet. The results suggest that the annual variations in different local time sectors are quite different due to the different sources. In the MLT sector 2200–0100, the annual variations with maxima in winter suggest they are caused by the combined effects of the convective electric field and the conductivity associated with particle precipitation. Furthermore, the conductivity seems to play a more important role in the MLT sector ∼2200–2320, while the convective electric field appears to be more important in the MLT sector ∼2320–0100. In the MLT sector 0300–0600, the annual variations with maxima in summer suggest they are caused by solar EUV conductivity effect and the equinoctial effect. The solar EUV conductivity effect works by increasing ionospheric conductivity and enhancing the westward electrojet in summer, while the equinoctial effect works by decreasing solar wind-magnetosphere coupling efficiency and weakening the westward electrojet in winter. In the MLT sector 0100–0300, the annual variations are relatively weak and can be attributed to the combined effects of annual variations caused by all the previously mentioned effects. In addition, we find that a significant annual variation in substorm occurrence rate, mainly occurring in the premidnight region, is quite similar to that in the westward electrojet. We suggest that elevated solar wind driving during the winter months contributes to higher substorm occurrence in winter in the Northern Hemisphere..
25. Claudia Stolle, Huixin Liu, CHAMP observations of the low latitude ionosphere and thermosphere and comparisons to physical models, AGU monograph: Modeling the Ionosphere-Thermosphere, 201, ?-?, 2014.02, During its more than 10 years mission the CHAMP (CHAllenging Min-isatellite Payload) satellite has revealed exciting and new observations of the upper F region ionosphere and the thermosphere. Special benifit has been gained from simultaneous observations of plasma and neutrals, and the magnetic field, which has led to many new findings and insight in the thermosphere-ionosphere system. This chapter reviews those new findings at low and equatorial latitudes, from the point of view of coupling between different atmospheric regions. On specific examples it is demonstrated that results of physical models have large impact in understanding new observations and related generation processes. However, further model development is still required to fully reproduce even large scale ionospheric and thermospheric features..
26. Nurul Shazana Abdul Hamid, Huixin Liu, Teiji Uozumi, Kiyohumi Yumoto, Equatorial  electrojet  dependence  on  solar  activity in  the  Southeast  Asia  sector, Antarctic Record, 57, 3, 329-337, 2013.12, The   equatorial   electrojet   (EEJ)   is   a   current   system   caused   by   the   enhanced   ionospheric   conductivity   near   the   dayside   magnetic   dip   equator.   We   examined   the   dependence   of   the   EEJ   on   solar   activity,   represented   by   the   10.7  cm   solar   radio   flux   (F10.7).  For  this  analysis,  we  used  a  new  equatorial  electrojet  index,  EUEL,  provided  by   the  MAGDAS/CPMN  network  in  the  Southeast  Asia  sector  for  the  year  2011.  Using  a  two-­ station  method,  the  EEJ  strength  was  calculated  as  the  difference  between  the  EUEL  index   of  the  dip  equator  station  and  the  EUEL  index  of  the  off-­dip  equator  station  located  outside   the   narrow   channel   (±3°in   latitudinal   range)   of   the   EEJ   band.   The   relationship   between   the  EEJ  component  and  the  F10.7  index  was  then  examined  using  power  spectrum  and   correlation   analyses.   We   found   approximate   24-­day   and   28-­day   periodicities   in   the   EEJ component,   which   are   in   phase   with   F10.7  variations.   On   the   other   hand,   the   daily   values   of  EEJ  showed  low  correlation  with  the  daily  F10.7  variations  during  the  study  period..
27. Hongru Chen, Liu Huixin, Toshiya Hanada, Storm-time atmospheric density modeling using neural networks and its application in orbit propagation, Adv. in Space Research, 10.1016/j.asr.2013.11.052, 53, 558-567, 2013.12, Upper atmospheric densities during geomagnetic storms are usually poorly estimated due to a lack of clear understanding of coupling mechanisms between the thermosphere and magnetosphere. Consequently, the orbit determination and propagation for low-Earth-orbit objects during geomagnetic storms have large uncertainties. Artificial neural networks are often used to identify nonlinear systems in the absence of rigorous theory. In the present study, an attempt has been made to model the storm-time atmospheric density using neural networks. Considering the debate over the representative of geomagnetic storm effect, i.e. the geomagnetic indices ap and Dst, three neu- ral network models (NNM) are developed with ap, Dst and a combination of ap and Dst respectively. The density data used for training the NNMs are derived from the measurements of the satellites CHAMP and GRACE. The NNMs are evaluated by looking at: (a) the mean residuals and the standard deviations with respect to the density data that are not used in training process, and (b) the accuracy of reconstructing the orbits of selected objects during storms employing each model. This empirical modeling technique and the compar- isons with the models NRLMSIS-00 and Jacchia-Bowman 2008 reveal (1) the capability of neural networks to model the relationship between solar and geomagnetic activities, and density variations; and (2) the merits and demerits of ap and Dst when it comes to char- acterizing density variations during storms..
28. Nurul Shazana Abdul Hamid, Huixin Liu, Teiji Uozumi, Kiyohumi Yumoto, Brief Study of Equatorial Electrojet and Global Sq Currents At Southeast Asia Region, IEEE International Conference on Space Science and Communication (IconSpace), 1-3 July 2013, 194-197, 2013.07, The equatorial electrojet (EEJ) is a strong eastward current flowing in a narrow band along the magnetic dip equator. This current interacts with the global Sq current and caused abnormally large amplitude of geomagnetic filed component measured at the magnetic dip equator station. In this study, we use a new EE-index (EDst and EUEL) derived from MAGDAS/CPMN stations to get continuous data of local EEJ magnetic component and global Sq magnetic component. In order to isolate EEJ component, we subtract the possible contributions of global Sq to the magnetometer measurements using a two-station method. The magnetic signature of EEJ strength is calculated as a difference between the EUEL index of dip equator station and the EUEL index of station few degrees away from dip equator. The global Sq current component at dip equator station is then given by the subtraction of EEJ component from EUEL index of dip equator station. Analysis is performed using data from two pairs of stations at Southeast Asia region for a year of 2011. We then examined seasonal variations of the both currents component together with longitudinal dependence of EEJ component in Southeast Asia region..
29. Huixin Liu, H. Jin, Yasunobu Miyoshi, H. Fujiwara, H. Shinagawa, Upper atmosphere response to stratosphere sudden warming: Local time and height dependence simulated by GAIA model, Geophys. Res. Lett., 10.1002/grl.50146, 40, 635-640, 2013.02, The whole atmosphere model GAIA is employed to shed light on atmospheric response to the 2009 major stratosphere sudden warming (SSW) from the ground to exobase. Distinct features are revealed about SSW impacts on thermospheric temperature and density above 100km altitude. (1) The effect is primarily quasi-semidiurnal in tropical regions, with warming in the noon and pre-midnight sectors and cooling in the dawn and dusk sectors. (2) This pattern exists at all altitudes above 100km, with its phase being almost constant above 200km, but propagates downward in the lower thermosphere between 100 and 200 km. (3) The northern polar region experiences warming in a narrow layer between 100 and 130km, while the southern polar region experiences cooling throughout 100–400 km altitudes. (4) The global net thermal effect on the atmosphere above 100km is a cooling of approximately ␣12 K. These characteristics provide us with an urgently needed global context to better connect and understand the increasing upper atmosphere observations during SSW events..
30. Huixin Liu, T. Hirano, S. Watanabe, Empirical model of the thermospheric mass density based on CHAMP satellite observations, J. Geophys. Res. , doi:10.1002/jgra.50144, 118, 843-848, 2013.02, The decadal observations from CHAMP satellite have provided ample information on the Earth’s upper thermosphere, reshaping our understandings of the vertical coupling in the atmosphere and near-Earth space. An empirical model of the thermospheric mass density is constructed from these high-resolution observations using the multivariable least-squares fitting method. It describes the density variation with latitude, longitude, height, local time, season, and solar and geomagnetic activity levels within the altitude range of 350–420 km. It represents well prominent thermosphere structures like the equatorial mass density anomaly (EMA) and the wave-4 longitudinal pattern. Furthermore, the empirical model reveals two distinct features. First, the EMA is found to have a clear altitude dependence, with its crests moving equatorward with increasing altitude. Second, the equinoctial asymmetry is found to strongly depend on solar cycle, with its magnitude and phase being strongly regulated by solar activity levels. The equinoctial density maxima occur significantly after the actual equinox dates toward solar minimum, which may signal growing influence from the lower atmosphere forcing. This empirical model provides an instructive tool in exploring thermospheric density structures and dynamics. It can also be easily incorporated into other models to have a more accurate description of the background thermosphere, for both scientific and practical purposes..
31. R. Shi, Huixin Liu, Akimasa Yoshikawa, Beichen Zhang, Binbin Ni, Coupling of electrons and inertial Alfven waves in the topside ionosphere, J. Geophys. Res. , doi:10.1002/jgra.50355, 118, 843-848, 2013.02.
32. Y. Yamazaki, A. D. Richmond, Liu Huixin, Kiyohumi Yumoto, Y. Tanaka, Sq current system during stratospheric sudden warming events in 2006 and 2009, J. Geophys. Res. , 10.1029/2012JA018116, 117, 2012.12.
33. Jusoh M. H., Kiyohumi Yumoto, Abdul Hamid N. S., Huixin Liu, Electromagnetic Coupling on Solar-Terrestrial System: Possible effects on seismic activities, Proceedings of ISAP2012, 1160-1163, 2012.11.
34. S. Tulasi Ram, N. Balan, B. Veenadhari, S. Gurubaran, S. Ravindran, T. Tsugawa, Liu Huixin, K. Niranjan, T. Nagatsuma, First observational evidence for opposite zonal electric fields in equatorial E and F region altitudes during a geomagnetic storm period, J. Geophys. Res. , 10.1029/2012JA018045, 118, 2012.09.
35. Y. Miyoshi, H. Fujiwara, H. Jin, H. Shinagawa, Huixin Liu, Numerical simulation of the equatorial wind jet in the thermosphere, J. Geophys. Res. , 10.1029/2011JA017373, 117, 2012.03.
36. Yasunobu Miyoshi, H. Jin, H. Fujiwara, H. Shinagawa, Huixin Liu, Wave-4 structure of the neutral density in the thermosphere and its relation to atmospheric tides, J. Atmos. Solar-Terres. Phys.,, 10.1016/j.jastp.2011.12.002, 90, 45-51, 2012.01.
37. Lühr, H., Huixin Liu, J. Park, S. Muller, , New Aspects of the Coupling Between Thermosphere and Ionosphere, with Special regards to CHAMP Mission Results, IAGA Special Sopron Book Series, 10.1007/978-94-007-0326-1_22, 2011.10.
38. Liu Huixin, M. Yamamoto, E. Doornbos, Equatorial Electrodynamics and Neutral Background in the Asian Sector During the 2009 Stratospheric Sudden Warming, J. Geophys. Res. , 10.1029/2011JA016607, 116, 2011.08.
39. Lühr, H. J. Park, P. Ritter, Huixin Liu, In-situ CHAMP observations of the ionosphere-thermosphere coupling, Space Sci. Rev., 10.1007/s11214-011-9798-4, 2011.07.
40. Huixin Liu, E. Doornbos, M. Yamamoto, S. T. Ram, Strong thermosphere cooling during the 2009 major statratosphere warming, Geophys. Res. Lett, 10.1029/2011GL047898, 38, 2011.06.
41. Huixin Liu, M. Yamamoto, Weakening of the mid-latitude summer night anomaly during geomagnetic storms, Earth. Planets and Space, 63, 371-375, 2011.06.
42. S. Tulasi Ram, M. Yamamoto, Huixin Liu, B. Veenadhari, S. Alex, Comment on “Westward electric field penetration to the dayside equatorial ionosphere during the main phase of the geomagnetic storm on 22 July 2009” by V. Sreeja et al., J. Geophys. Res., 10.1029/2010JA016634, 116, 2011.06.
43. S. V. Thampi, M. Yamamoto, C. Lin, Huixin Liu, Comparison of FORMOSAT‐3/COSMIC radio occultation measurements with radio tomography, Radio Science, 10.1029/2010RS004431, 46, 2011.05.
44. Y. Miyoshi, H. Fujiwara, H. Jin, H. Shinagawa, Huixin Liu, and K. Terada, Model study on the formation of the equatorial mass density anomaly in the thermosphere, J. Geophys. Res., 10.1029/2010JA016315, 116, 2011.05.
45. T. Kondo, A. D. Richmond, Huixin Liu, J. Lei, S. Watanabe, On the formation of a fast thermospheric zonal wind at the magnetic dip equator, Geophys. Res. Lett., 10.1029/2011GL047255, 38, 2011.05.
46. C. Stolle, Huixin Liu, V. Truhlík, H. Lühr, P. G. Richards, Solar flux variation of the electron temperature morning overshoot in the equatorial F region, J. Geophys. Res., 10.1029/2010JA016235, 116, 2011.04.
47. Thampi, S. V., N. Balan, C. Lin, Liu Huixin, M. Yamamoto, Mid-latitude summer nighttime anomaly (MSNA) – observations and model simulations, Ann. Geophys., , 29, 157, 165, 157-165, 2011.04.
48. Adachi, T., M. Yamaoka, M. Yamamoto, Y. Otsuka, Liu Huixin, C. Hsiao, A. Chen, R. Hsu, Midnight latitude-altitude distribution of 630-nm airglow in the Asian sector measured with Formosat-2/ISUAL, J. Geophys. Res, 10.1029/2009JA015147, 115, A09315, 2010.07.
49. Thampi, S. V., M. Yamamoto, Liu Huixin, S. Saito, Y. Otsuka, A. K. Patra, Nighttime-like Quasi Periodic echoes induced by a partial solar eclipse, Geophys. Res. Lett., 10.1029/2010GL042855, 37, L09107, 2010.07.
50. Liu Huixin, Thampi, S. V., M. Yamamoto, Phase reversal of the diurnal cycle in the mid-latitude ionosphere, J. Geophys. Res, 10.1029/2009JA014689, 115, A01305, 2010.06.
51. Thampi, S. V., C. Lin, Liu Huixin, M. Yamamoto, First Tomographic Observations of the Mid-latitude Summer Nighttime Anomaly (MSNA) over Japan, J. Geophys. Res. , 10.1029/2009JA014439, 114, A10318, 2009.07.
52. Liu Huixin, M. Yamamoto, H. Luehr, Wave-4 pattern of the equatorial mass density anomaly- A thermospheric signature of tropical deep convection, Geophys. Res. Lett., 10.1029/2009GL039865, 36, L18104, 2009.06.
53. Liu Huixin, H. Luehr, S. Watanabe, A solar terminator wave in thermospheric wind and density simultaneously observed by CHAMP, Geophys. Res. Lett., 10.1029/2009GL038165, 36, L10109, 2009.05.
54. Liu Huixin, S. Watanabe, T. Kondo, Fast thermospheric wind jet at the Earth's dip equator, Geophys. Res. Lett., 10.1029/2009GL037377, 36, L08103, 2009.03.
55. Liu Huixin, S. Watanabe, Seasonal variation in the longitudinal structure of the equatorial ionosphere: does it reflect tidal influences from below? , J. Geophys. Res. , 10.1029/2008JA013027, 113, A08315, 2008.01.
56. Liu Huixin, H. Luehr, S. Watanabe, W. Koehler, M. Manoj, Contrasting behavior of the thermosphere and ionosphere to the Oct. 28, 2003 solar flare, J. Geophys. Res., 10.1029/2007JA012313, 112, A07305, 2007.05.
57. Liu Huixin, H. Luehr, S. Watanabe, V. Henize, W. Koehler, P. Visser, Zonal winds in the equatorial upper thermosphere: Decomposing the solar flux, geomagnetic activity, and seasonal dependencies, J. Geophys. Res., 10.1029/2005JA011415, 111, A07307, 2007.05.
58. Liu Huixin, C. Claudia, M. Forster, S. Watanabe, Solar activity dependence of the electron density at 400 km at equatorial and low latitudes observed by CHAMP, J. Geophys. Res., 10.1029/2007JA012616, 112, A11311, 2007.03.
59. Liu Huixin, H. Luehr, S. Watanabe, Climatology of the Equatorial Thermospheric Mass Density Anomaly, J. Geophys. Res., 10.1029/2006JA012199, 112, A05305, 2007.01.
60. Liu Huixin, C. Claudia, S. Watanabe, T. Abe, D. Cooke, Evaluation of the IRI Model Using CHAMP Observations in Polar and Equatorial Regions, Adv. in Space. Res., , 39, 904-909, 2007.03.
61. Liu Huixin, H. Luehr, Strong disturbance of the upper thermospheric density due to magnetic storms: CHAMP observations, J. Geophys. Res., 10.1029/2004JA010908, 110, A09S29, 2005.10.
62. Liu Huixin, H. Luehr, V. Henize, W. Koehler, Global distribution of the thermospheric total mass density derived from CHAMP, J. Geophys. Res., 10.1029/2004JA010741, 110, A04301, 2005.05.
63. Liu Huixin, G. Lu, Velocity shear-related ion upflows in the low-altitude ionosphere, Ann. Geophysics., 22, 1149-1153, 2004.10.
64. Liu Huixin, S. Y. Ma, K. Schlegel, Diurnal, seasonal, and geomagnetic variations of large field-aligned ion upflows in the high-latitude ionospheric F region, J. Geophys. Res, 106, 24,651-24,662, 2001.06.
65. Liu Huixin, K. Schlegel, S. Y. Ma, Combined ESR and EISCAT observations of the dayside polar cap and auroral oval during the May 15, 1997 storm, Ann. Geophysics., 18, 1067-1072, 2000.10.
Presentations
1. Liu Huixin, Y. Sun, Y. Miyoshi, H. Jin, ENSO effects on MLT diurnal tides: a 21-year reanalysis-drive GAIA model simulation, AOGS2018, 2018.06.
2. Liu Huixin, Medium-scale GW activity in bottomside F region
(GPS 通信障害の原因となるプラズマバブルの発生源に迫る), JpGU meeting 2018, international session, 2018.05.
3. Liu Huixin, Y. Nakamoto, Y. Miyoshi, Thermosphere response to CO2 doubling: GAIA simulation results, 10th international workshop on Long-term trends, 2018.05.
4. Liu Huixin, Role of Medium-scale GW in seeding plasma bubbles, NIPR symposium 2017, 2017.12.
5. Liu Huixin, Medium-scale GW activity in bottomside F region
, SGEPSS 2017, 2017.10.
6. Liu Huixin, Y. Nakamoto, Y. Miyoshi, Thermosphere response to CO2 doubling: GAIA simulation results, AOGS2017, 2017.08.
7. Liu Huixin, Y. Sun, Y. Miyoshi, H. Jin, ENSO effects on MLT diurnal tides: a 21-year reanalysis-drive GAIA model simulation, AGU-JpGU joint meeting 2017, 2017.05.
8. Liu Huixin, Thermosphere interannual variability: potential fingerprints of QBO and ENSO, JAXA symposium, 2016.12.
9. Liu Huixin, Thermosphere interannual variability: implications for ENSO and QBO, The International Whole Atmospherear Symposium, 2016.09.
10. Liu Huixin, Thermosphere interannual variability: ENSO effects, Mesosphere-Thermosphere-ionosphere workshop, 2016.08.
11. Liu Huixin, Thermosphere and Ionosphere response to solar flares, VarSITI/ SCOSTEP symposium, 2016.06.
12. Liu Huixin, Thermosphere response to stratosphere sudden warming simulated by GAIA, ISEA2015, 2015.10.
13. K. Oyama, K. Ryu, Liu Huixin, Earthquake Ionosphere Precursor Study Group and Its Role - Toward Strengthening Earthquake Study, AOGS2015, 2015.08.
14. K. Oyama, K. Ryu, Liu Huixin, Diversity of Ionosphere Modification Possibly Caused by Large Earthquakes, AOGS2015, 2015.08.
15. K. Ryu, K. Oyama, Liu Huixin, Contribution of the Mid-Latitude Seismic Activity to the EIA Intensity Variation Suggested by Satellite Electron Density Measurements, AOGS2015, 2015.08.
16. L. Chang, Liu Huixin, Yasunobu Miyoshi, Structure and Origins of the Weddell Sea Anomaly From Tidal and Planetary Wave Signatures in FORMOSAT-3/COSMIC Observations and GAIA GCM Simulations, AOGS2015, 2015.08.
17. N. S. A. Hamid, Liu Huixin, EEJ Empirical Model Based on Ground-Based Magnetometer Data, AOGS2015, 2015.08.
18. Liu Huixin, Periodic Variations in the Thermospheric Density, AOGS2015, 2015.08.
19. Liu Huixin, Thermosphere responses to SSWs simulated by GAIA model, CEDAR 2015, 2015.06.
20. Liu Huixin, Periodic variations in the thermospheric density, JpGU meeting 2015, international session, 2015.05.
21. Liu Huixin, Thermal and dynamical response of the thermosphere to stratosphere sudden warming, SCOSTEP 2014, 2014.10.
22. Liu Huixin, Upper atmosphere response to stratosphere sudden warming events, SCOSTEP, 2014.10.
23. J. Jhou, Y. Oyama, C. Lin, Liu Huixin, Ionospheric Response to 2009 Sudden Stratosphere Warming in the Northern and Southern Hemisphere, AOGS2014, 2014.07.
24. M. Förster, Liu Huixin, C. Stolle, Solar Activity and Seasonal Effects of the Upper Atmosphere at High Latitudes According to Observations and Modelling, AOGS2014, 2014.07.
25. Shin Suzuki, J. Park, Y. Otsuka, Liu Huixin, H. Luehr, Coordinated Measurements of Medium-scale Traveling Ionospheric Disturbances with Ground-based Airglow Imagers and CHAMP Satellite, AOGS2014, 2014.07.
26. N. S. A. Hamid, Liu Huixin, Local Time and Longitudinal Dependence of Equatorial Electrojet Calculated from Ground-based Magnetometer, AOGS2014, 2014.07.
27. Liu Huixin, Thermosphere Cooling at Low and Middle Latitudes During Stratosphere Warming Events: GAIA Model Simulations, AOGS2014, 2014.07.
28. Rinako TAKAZAKI, Liu Huixin, Saburo Miyahara, The Ionospheric Sq Current Systems Influenced by Semidiurnal Tide During Sudden Stratospheric Warming Events Simulated by the Kyushu-GCM, AOGS2014, 2014.07.
29. Guo Jianpeng, Liu Huixin, MLT and seasonal dependence of auroral electrojets: IMAGE magnetometer network observations, JpGU meeting 2014, international session, 2014.05.
30. Liu Huixin, Hermann Luehr, Enhancing our understanding of the atmosphere-ionosphere coupling with Low Earth Orbiting satellite missions, JpGU meeting 2014, international session, 2014.04.
31. Liu Huixin, Global mean cooling of the thermosphere during the 2009 major SSW, Scientific committee on Solar-Terrestrial Physics: Internatinoal CAWSES-II symposium, 2013.11, Recent satellite observations have demonstrated clear response of the thermosphere to major stratosphere sudden warming event in 2009. This response exhibits two prominent features. One is a semidiurnal perturbation, the other is a global mean cooling of ~12 Kelvin [Liu et al., 2011, 2013]. The semidiurnal perturbation is now known to be due to the enhancement of the semi- diurnal tides during SSW periods. The cause of the global mean cooling, however, remains unexplained. This paper explores the possible mechanism leading to the global mean cooling by examining all energy balance terms simulated by the GAIA model, which is a self-consistent, fully coupled model of the Earth’s lower atmosphere, thermosphere, and ionosphere..
32. Liu Huixin, Deguchi Ryo, Ionospheric current system derived from CHAMP using DECS method at low and middle latitudes, Scientific committee on Solar-Terrestrial Physics: Internatinoal CAWSES-II symposium, 2013.11, The technique of 1-dimensional spherical elementary current systems (1D SECS) is one way to determine ionospheric and field-aligned currents (FAC) from magnetic field measurements made by LEO satellites. The SECS method consists of two sets of basis functions: divergence-free (DF) and curl-free (CF), which cause poloidal and toroidal magnetic fields, respectively. The original 1D-SECS method is only applicable at high latitudes, where the FAC can be assumed to be radial. At low/mid latitudes, however, it is not applicable because the FAC is far from being radial. In this study, we modify the original 1D-SECS by reconstructing the current system on a dipole coordinate. This allows the method to be applicable at all latitudes. We name this method Dipole Elementary Current Systems (DECS).

By applying the DECS to the CHAMP magnetic field measurements, we have derived the ionospheric currents including the DF, CF and FAC components. The DF components find good agreement with that derived from MAGDAS/CPMN 210 MM ground magnetometer chain using traditional method (90 deg rotation), lending support for the reliability of DECS at middle and low latitude. In this study, we will focus on results about the cross-hemispheric FAC.
.
33. Liu Huixin, Nurul Shazana Abdul Hamid, The equatorial electrojet and global Sq current components at dip equator, Scientific committee on Solar-Terrestrial Physics: Internatinoal CAWSES-II symposium, 2013.11, The equatorial electrojet (EEJ) is a strong eastward current flowing in a narrow band along the dip equator. This current interacts with the global Sq current before decreases to zero near 3° dip latitude at both hemispheres. In this study, we used observation data together with CM4 model (Sabaka et al., 2004) in order to isolate global Sq contribution from EEJ at the dip equator station. The observation data used are the new equatorial EUEL index calculated from geomagnetic northward component from MAGDAS network (Yumoto and the CPMN Group, 2001). Normalization of EUEL from off equator station to dip equator gives normalized Sq. EEJ component is calculated as the different between the normalized EUEL from station near dip equator with normalized Sq.
The relation between EEJ and Sq at the dip equator is examined from three particular aspects. The first aspect is the longitudinal dependence. Observatories data from different longitude sectors are used in this study. A good linear relation between EEJ and Sq is obtained. The second aspect is the dependence on solar activity. EEJ-Sq relationship is found to have a weak dependence on solar activity. The last aspect is the dependence on seasons. The relation between EEJ and Sq apparently has a strong seasonal dependence as they are stronger in local summer compared to local winter. At the same time, analysis using cross spectrum shows that their relationship differs in different time scale. This suggests that EEJ-Sq relationship dependence on time scale and this aspect has to be considered in the future study.
.
34. Liu Huixin, vertical coupling processes in the Earth's system, NASA review panel, 2013.08.
35. Liu Huixin, Thermosphere response to lower atmosphere forcing: decadal observations from the CHAMP mission, Workshop  on  Whole  Atmosphere   Coupling  During  Solar  Cycle  24 , 2013.07.
36. Nurul  Shazana  Abdul  Hamid, Liu Huixin, Brief Study of Equatorial Electrojet and Global Sq Currents At Southeast Asia Region, IEEE International Conference on Space Science and Communication (IconSpace), 2013.07.
37. N. A. A. Hamid, Liu Huixin, Kiyohumi Yumoto, Relation Between the Local Equatorial Electrojet and Global Sq Current Calculated from Different Longitude Sectors, AOGS2013, 2013.06.
38. Nurul  Shazana  Abdul  Hamid, Liu Huixin, Relation Between the Local Equatorial Electrojet and Global Sq Current Calculated from Different Longitude Sectors, Asia Oceania Geosciences Society, 2013.06, The equatorial electrojet (EEJ) is a strong eastward
current flowing in a narrow band along the magnetic dip equator. This current
interacts with the global Sq current before decreases to zero near 3°
dip latitude at both hemispheres. In this study, we examined the relation between the local EEJ
component and global Sq current component obtained using two stations method. Analysis
was carried using the new equatorial electrojet index, EUEL, calculated from geomagnetic northward, H, component from different longitude sectors.
The magnetic EEJ strength is calculated as the difference between the EUEL index of the magnetic dip equator
station and the EUEL index of the off
magnetic dip equator station located beyond EEJ band. The global Sq component
is then obtained by subtracting the EEJ component from the EUEL index. Long term data from 2005-2011 are used in this study. The
relation between these currents component are then examined from four
particular aspects. The first aspect is the daily and seasonal variations of
both currents components. The result shows that the amplitude of local EEJ
component is always higher than the global Sq component. The second aspect is
the day to day variation of these currents and the third aspect is their dependence on solar activity represented by
the 10.7cm solar radio flux (F10.7). The last aspect is the
longitudinal dependence where the correlation between
these currents component from different longitude sectors are quantified using calculated correlation
coefficient..
39. Liu Huixin, Upper atmosphere response to stratosphere sudden warming: local time and height dependence simulated by GAIA model, JpGU meeting 2013, international session, 2013.05.
40. Liu Huixin, Mohamad Huzaimy Bin Jusoh, Possible relationship between Solar Wind Input Energy and Seismicity, JpGU meeting 2013, international session, 2013.05.
41. Nurul Shazana Abdul Hamid, Liu Huixin, Relation between the local equatorial electrojet and global Sq current calculated from different longitude sectors, JpGU meeting 2013, international session, 2013.05.
42. Deguchi Ryo, Liu Huixin, Modification of one-dimensional spherical elementary current systems for applying at low/mid latitude, JpGU meeting 2013, international session, 2013.05.
43. Jusoh Mohamad Huzaimy, Liu Huixin, Yumoto Kiyohumi, Investigation on the Possible Relationship between Magnetic Pulsations and Earthquakes, AGU fall meeting 2012, 2012.12.
44. Liu Huixin, Upper thermosphere coupling with the lower atmosphere: the known and unknown, 地球電磁気・地球惑星圏学会, 2012.11.
45. Jusoh Mohamad Huzaimy, Liu Huixin, Yumoto Kiyohumi, Exploration of the Possible Relationship between Magnetic Pulsations and Earthquakes, 地球電磁気・地球惑星圏学会, 2012.11.
46. Shi Run, Liu Huixin, Yoshikawa Akimasa, 1D simulation of Electron acceleration by Inertial Alfven wave pulse, 地球電磁気・地球惑星圏学会, 2012.11.
47. Liu Huixin, Jin, H, Miyoshi Yasunobu, Fujiwara Hitoshi, Shinagawa, H., GAIA model simulation of the thermosphere response to SSW, 地球電磁気・地球惑星圏学会, 2012.11.
48. ABDUL HAMID NURUL SHAZANA, Liu Huixin, Relation between the local equatorial electrojet and global Sq current system, 地球電磁気・地球惑星圏学会, 2012.11.
49. Liu Huixin, Upper atmosphere response to major and minor stratosphere sudden warming , ISEA13, 2012.03, Stratosphere sudden warming (SSW) is a local meteorological event with a global impact. Strong semi-diurnal perturbation in the vertical plasma drift and TEC has been frequently reported. A general depletion of the plasma and thermospheric density has also been observed during the 2009 major SSW, indicating a substantial cooling in the upper atmosphere (Liu et al., JGR 2011, GRL 2011). Now we ask, are these features common to all SSW? What are the differences between responses to major and minor SSW? Using ground and satellite observations, ionospheric electrodynamics, thermosphere variation and the global Sq current are investigated in Asian, Africa and Peruvian sectors to elucidate the above questions..
50. Liu Huixin, Equatorial electrodynamics and neutral background in the Asian sector during the 2009 Stratosphere sudden warming , AOGS, 2011.08.
51. Liu Huixin, Upper-lower atmosphere coupling: known and unknowns, IUGG 2011 General Assembly, 2011.07, Recently rapidly growing observations have revealed clear evidences for a close coupling between the upper thermosphere and the lower atmosphere. Some of these evidences are seen in the spatial structures (e.g. the terminator wave, the wave-4 structure), while others are more prominent in the temporal variations (e.g.16-day wave, and the Stratospheric Sudden Warming effect). In this talk, I try to review several aspects of the coupling by showing representative phenomena and their related known and unknown..
Membership in Academic Society
  • Japan Meteorogical Society
  • Japan Geophysical Union
  • Asia Oceania Geophysical Society
  • Society of Geomagnetism and Earth, Planetary and Space Science
Awards
  • Research on the thermosphere-ionosphere interaction using satellite-bourne accelerometer observations
  • Plasma-neutral interaction in the mesosphere-thermosphere-ionosphere system
  • The Thermosphere-Ionosphere Coupling at Low Latitudes
  • Global Thermosphere-Ionosphere coupling study base on CHAMP satellite observations
  • Studying the polar ionosphere response to magnetic storms with the international EISCAR radar system
Educational
Educational Activities
1. Earth and Planetary Science: an introduction
2. Cosmic science
3. Geospace physics
4. Space electrodynamcs
5. Helio-Geospace electromagnetism
6. Kikan seminar
7. Introduction to Physics: B
Social
Professional and Outreach Activities
Formation of Preliminary Center for Capacity Building for Space Weather Research. JSPS Core-to-Core Program, 2012 ISWI and MAGDAS School on Space Science
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