Nawo Eguchi

Circulation changes in the stratosphere and mesosphere during the stratospheric sudden warming event in January 2009

In this study, general circulation changes are investigated during the stratospheric sudden warming event in January 2009 by the use of Aura Earth Observing System Microwave Limb Sounder observations to show dynamical coupling of stratosphere and mesosphere. It is revealed that the reversal from westerly winds to easterly winds occurred earlier in the mesosphere in comparison with the stratopause level and suggested that the earlier reversal in the mesosphere may be caused by large-scale waves formed in the lower mesosphere due to barotropic and/or baroclinic instability there. Such instability is considered to be brought about by the intensification of the westerly jet with double maxima in the polar night stratosphere and subtropical mesosphere before the warming occurrence. Furthermore, it is shown that an independent meridional circulation cell might be formed by the earlier reversal of zonal winds in the mesosphere.

The role of convective overshooting clouds in tropical stratosphere–troposphere dynamical coupling

Abstract. This paper investigates the role of deep convection and overshooting convective clouds in stratosphere–troposphere dynamical coupling in the tropics during two large major stratospheric sudden warming events in January 2009 and January 2010. During both events, convective activity and precipitation increased in the equatorial Southern Hemisphere as a result of a strengthening of the Brewer–Dobson circulation induced by enhanced stratospheric planetary wave activity. Correlation coefficients between variables related to the convective activity and the vertical velocity were calculated to identify the processes connecting stratospheric variability to the troposphere. Convective overshooting clouds showed a direct relationship to lower stratospheric upwelling at around 70–50 hPa. As the tropospheric circulation change lags behind that of the stratosphere, outgoing longwave radiation shows almost no simultaneous correlation with the stratospheric upwelling. This result suggests that the stratospheric circulation change first penetrates into the troposphere through the modulation of deep convective activity.

First observations of CO2 absorption spectra recorded in 2005 using an airship-borne FTS GOSAT TANSO–FTS BBM in the SWIR spectral region

This article describes the results of a field experiment performed to confirm the feasibility of measuring the solar spectra absorbed by carbon dioxide (CO2) using a short wavelength infrared Fourier transform spectrometer (SWIR-FTS) installed onboard an airship. These airship-borne observations, conducted on 7 April 2005, represent the first aircraft-borne spectroscopic experiment on greenhouse gases (GHGs) in Japan and were performed as part of the Greenhouse Gases Observing Satellite (GOSAT) project. To develop and demonstrate an effective retrieval algorithm to derive CO2 column amounts from spectroscopic observations, ground-surface scattered solar absorption spectra were observed by SWIR-FTS installed onboard the airship. This instrument is a breadboard model (BBM) of the Thermal and Near-infrared Sensor for Carbon Observation (TANSO) of GOSAT, which was successfully launched on 23 January 2009. The spectra of CO2 observed using the BBM were compared with the simulated spectra calculated by a radiative transfer code based on airship-borne in situ measurement data, which were obtained at the time of FTS measurements. The two sets of spectra are in agreement within 5%, and we identified solutions to several technical problems related to the FTS instrument, thereby improving the signal-to-noise ratio (SNR).

Maritime-Continental Contrasts in the Properties of Low-Level Clouds: A Case Study of the Summer of the 2003 Yamase, Japan, Cloud Event

Satellite data were used to investigate maritime-continental differences in the characteristics of the low-level cloud (the Yamase cloud) that covered northeast Japan during the summer of 2003. The features of the Yamase cloud were found to be almost the same as those of general stratus clouds but with a smaller effective radius () and a greater optical thickness () over land, as compared with general stratus clouds. The values of over land (average, 11.8 μm) were smaller than those over the ocean (13.5 μm), and the values of and the cloud water path over land (20 and 145 gm−2, resp.) showed larger spatial variances than those over the ocean (10 and 86 gm−2, resp.), although the cloud top altitude was nearly the same over both ocean and land (1–3 km). We suggest that this maritime-continental contrast is a result of the combined effects of topography and aerosols characteristics. The Yamase wind blowing from the ocean is forced upwards in coastal regions by the steep mountainous terrain. The updraft drives the inhomogeneity in cloud parameters, and a convective-like cloud develops without precipitation. The relationship between and suggests high aerosol concentrations and unstable conditions over land.

Seasonal variations of greenhouse gas column-averaged dry air mole fractions retrieved from SWIR spectra of GOSAT TANSO-FTS

GOSAT has monitored column-averaged dry air mole fractions of CO2 and CH4 (XCO2 and XCH4, respectively) for cloud-free scenes more than 2 years. The present paper shows the occurrence of the cloud-free data and the seasonal and inter-annual variation of XCO2 and XCH4. The seasonal variation of XCO2 in the boreal hemisphere consists with the previous knowledge from ground-based observation and atmospheric transport model but the relatively small seasonal amplitude of column amount. The globally averaged XCO2 suggests that the CO2 concentrations in the atmosphere have increased since 2009 with approximately 2 ppmv. The high temporal variations of XCH4 are found over the northern subtropics, especially the eastern Asia, however, where the cloud covers frequently during the rainy season. To more precise analysis, it is necessary to accumulate the effective data for analysis or to validate the effect of cloud on retrieved data.