||Nawo Eguchi and Yukio Yoshida, A high-level cloud detection method utilizing the GOSAT TANSO-FTS water vapor saturated band, Atmospheric Measurement Technique, 10.5194/amt-12-389-2019, 12, 1, 389-403, 2019.01.
||Nawo Eguchi, Kunihiko Kodera, Beatriz M. Funatsu, Hisahiro Takashima, and Rei Ueyama, Rapid convective transport of tropospheric air into the tropical lower stratosphere during the 2010 sudden stratospheric warming, Scientific Online Letters on the Atmosphere, 10.2151/sola.12A-003, 12A, Special Edition, 13-17, 2016.08.
||Nawo Eguchi, Kunihiko Kodera, and Tomoe Nasuno, A global non-hydrostatic model study of a downward coupling through the tropical tropopause layer during a stratospheric sudden warming, Atmospheric Chemistry and Physics, 10.5194/acp-15-297-2015, 15, 1, 297-304, 2015.01.
||Nawo Eguchi, Tadahiro Hayasaka, and Masahiro Sawada, Maritime-Continental Contrasts in the Properties of Low-Level Clouds: A Case Study of the Summer of the 2003 Yamase, Japan, Cloud Event, Advances in Meteorology, 10.1155/2014/548091, 2014, 548091, 1-16, 2014.03.
||Nawo Eguchi, YukioYoshida, Isamu Morino, Nobuyuki Kikuchi, Tazu Saeki, Makoto Inoue Osamu Uchino, Shamil Maksyutov, Hiroshi Watanabe, and Tatsuya Yokota, Seasonal variations of greenhouse gas column-averaged dry air mole fractions retrieved from SWIR spectra of GOSAT TANSO-FTS, 2011 IEEE Geoscience and Remote Sensing Symposium, 10.1109/IGARSS.2011.6049986, 3542-3545, 2011.10.
||Nawo Eguchi, Ryu Saito, Tazu Saeki, Yumiko Nakatsuka, Dmitry Belikov, and Shamil Maksyutov, A priori covariance estimation for CO2 and CH4 retrievals, Journal of Geophysical Research-Atmosphere, 10.1029/2009JD013269, 115, D10, D10215 1-16, 2010.05, We derive the a priori covariance matrices of CO2 and CH4 for the retrieval of their profiles and columns from satellite spectral data. The monthly a priori covariance matrices of CO2 and CH4 at each grid cell (0.5° × 0.5°) on the globe are calculated using simulated data from the atmospheric tracer transport model. The a priori covariance matrix is defined as the sum of the bias and noise components, where the bias is obtained from the difference in seasonal cycle between simulated data and observation-based reference data, and the noise is defined as synoptic and interannual variations. The use of simulated data as well as observation-based reference data enables realistic variance and covariance values to be obtained for each temporal component. The seasonal bias is approximately 2 ppm for CO2 and 20 ppb for CH4. A large difference in synoptic variations is obtained between simulated and reference data over the source region, especially over land. The interannual variances derived from the reference data show maximum values (4 ppm2 for CO2 and 220 ppb2 for CH4) in northern midlatitudes. Global data sets of a priori covariance matrices for CO2 and CH4 are now available for the retrieval of concentrations using satellite spectral data. Furthermore, the data set has the potential to be applied in studies in other fields, including estimates of CO2 flux error using inverse modeling and planning for ground-based observation networks..
||Nawo Eguchi and Kunihiko Kodera, Impacts of stratospheric sudden warming event on tropical clouds and moisture fields in the TTL : A case study, scientific online letters on the atmosphere, 10.2151/sola.2010-035, 6, 1, 137-140, 2010.10, The impact of stratospheric sudden warming event in September 2007 on the tropics was investigated based on satellite data (CALIOP, MLS and TRMM PR). Equatorial temperature and water vapor at 100 hPa decreased by about 1 K and 1 ppmv within 10 days, respectively. Changes in tropical clouds are observed together with the occurrence of the SSW as i) frequent formation of higher-level cirrus clouds over the Maritime Continent, to where water vapor was transported from Asian Monsoon and where the lowest temperature occurred, ii) intensification of deep convective activity in the TTL over African continent, and iii) southward shift of the convective clouds over South American continent..
||Nawo Eguchi and Tatsuya Yokota, Investigation of clear-sky occurrence rate estimated from CALIOP and MODIS observations, Geophysical Research Letters, 10.1029/2008GL035897, 35, 23, L23816 1-5, 2008.12, We derived the global distribution of the clear-sky occurrence rate during the daytime using Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and Moderate-resolution Imaging Spectrometer (MODIS) data. Our goal was to estimate the frequency of likely successful CO(2) and CH(4) column concentration retrievals by the Greenhouse gases Observing Satellite (GOSAT). Clear-sky regions over land were frequently found around desert regions throughout the year, and at northern mid-latitudes in the winter hemisphere. Overall, clear-sky regions covered approximately 11% of the globe annually, on average. From a comparison of the CALIOP and MODIS cloud data for June 2007, we found that MODIS overestimated the clear-sky ratio by approximately 5%, except for in the tropics..
||Nawo Eguchi and Masato Shiotani, Intraseasonal variations of water vapor and cirrus clouds in the tropical upper troposphere, Journal of Geophysical Research-Atmosphere, 10.1029/2003JD004314, 109, D12, D12106 1-11, 2004.06, Space-time variations of tropical upper tropospheric water vapor and cirrus clouds associated with the intraseasonal oscillation (ISO) are investigated using data from the Microwave Limb Sounder (MLS) and the Cryogenic Limb Array Etalon Spectrometer (CLAES) on board the Upper Atmosphere Research Satellite (UARS). Composite moisture and meteorological fields based on five ISO events selected in two boreal winters (1991–1993) are analyzed using 20–80 day band-pass-filtered data. At 215 and 146 hPa, wet anomalies with frequent appearance of cirrus clouds exist over the convective system and move eastward from the Indian Ocean to the central Pacific, suggesting a direct effect of convective activity up to this level. At 100 hPa, however, the moisture field seems to be indirectly affected by convective activity through the dynamical response to the convective heating. Dry anomalies are observed over the Indian Ocean around the developing stage and over the eastern Pacific around the mature-to-decaying stage of the ISO. Cirrus clouds are frequently found over the cold region located to the east of the convective system. These structures around the tropopause level are closely related to the eastward moving Kelvin and Rossby wave responses to the convective heating with the equatorial cold anomaly and with the subtropical anticyclonic gyres. Between the two gyres the easterly wind blowing through the equatorial cold region may cause dehydration through cirrus formation when the convective system develops over the Indian Ocean and the western Pacific. As the northern gyre intensifies, tropical dry air is transported to the subtropical Pacific and eventually to the equatorial eastern Pacific. It is suggested that the temperature and flow variations due to the coupled Kelvin-Rossby wave structure play an important role in dehydrating air in the tropical and subtropical tropopause region..
||Tatsuya Yokota, Yukio Yoshida, Nawo Eguchi, Yoshifumi Ota, Tomoaki Tanaka, Hiroshi Watanabe and Shamil Maksyutov, Global Concentrations of CO2 and CH4 Retrieved From GOSAT: First Preliminary Results, Scientific Online Letters on the Atmosphere, 10.2151/sola.2009‒041, 5, 1, 160-163, 2009.10, The Greenhouse Gases Observing Satellite (GOSAT) was launched on January 23, 2009, to monitor global atmospheric levels of CO2 and CH4 from space. GOSAT started initial operation of its instruments after an initial satellite system check. Although the radiant data obtained by the GOSAT instruments are currently in the preliminary stages of calibration and validation, the spectral absorption features of CO2 and CH4 are clearly identifiable. An initial retrieval of these gaseous concentrations was performed for measurement scenes of cloud-free conditions over land. These results showed that column-averaged dry air mole fractions of both CO2 and CH4 in the northern hemisphere were higher than those in the southern hemisphere. These latitudinal differences agree with data obtained from groundbased sources and other satellite observations; however, the absolute values of the gaseous concentrations from GOSAT data seem to have been underestimated. Calibrations as well as validation should be conducted to improve the quality of GOSAT retrievals..