CO2 concentrations in the upper troposphere were retrieved from thermal infrared spectra as observed by the only spaceborne hyperspectral sounder launched in the 1990s: the Interferometric Monitor for Greenhouse gases (IMG) onboard the Advanced Earth Observing Satellite (ADEOS). First, the effective optical path difference of the IMG was evaluated because the actual instrumental line shape function of the interferometer component has not been evaluated for technical reasons in the orbit. The CO2 retrieval method was based on the maximum a posteriori (MAP) retrieval method and on procedures to decrease errors that obstruct CO2 signal detection. For the retrieval analysis, ERA-40 re-analysis meteorological data were used as temperature field data. A method of selecting effective channels for CO2 retrieval was used to remove channels with a high temperature dependency and to reduce errors in estimating the water vapor, ozone, and surface temperature. Furthermore, uncertainties in temperature and other error factors, which cannot be removed through channel selection, were evaluated and optimized by treating them as components of measurement errors in the MAP retrieval. CO2 retrieval noises of the MAP retrieval were estimated as 2.5 % and 2.0 % at pressure levels of 500 and 300 hPa, respectively. CO2 concentrations retrieved from IMG data were compared with aircraft measurement data. Results showed that the random error in the IMG retrieval was smaller than that estimated as the a posteriori error of the MAP retrieval. No significant biases were shown compared with the margin of random errors. The CO2 retrieval method was applied to IMG data measured in April, 1997. Although assuming a uniform CO2 concentration as a priori, the latitudinal gradient of the zonal mean concentration was consistent with climatological features presented by previous studies at pressure levels of 500 and 300 hPa. These results suggest that thermal infrared observation by the IMG is effective for evaluating the upper tropospheric CO2 concentration in the 1990s.
A new formulation for eddy viscosity and thermal eddy diffusivity is presented to constitute a turbulence closure model applicable to the terra incognita range. The Deardorff model, which is widely used for a Large-Eddy Simulation (LES), is extended to consider the effect of anisotropic nature in the turbulent flux. The anisotropic length scales applied to the extended Deardorff model are empirically determined as a function of the model resolution using the results of the a priori LES analysis. The new model is examined with various horizontal resolutions for a convective boundary layer and is compared with the original Deardorff model. The new model improves the representation of the vertical heat flux and the magnitude of the resolved convection even for the resolutions including the terra incognita range. The original model tends to underestimate the subgrid heat flux by increasing the grid size; this underestimation causes artificial energy accumulation at higher wavenumbers. The proposed model suggests the feasibility of a turbulence scheme applicable to the terra incognita range, although the subgrid component tends to be overestimated in the LES range and the vertical temperature gradient in the surface layer is weakened for coarser model resolution.
Cyclonic misovortices with a horizontal scale of 0.4-1.9 km embedded within a convective snowband were observed by two X-band Doppler radars in the Japan Sea coastal region on December 31, 2007, during a cold-air outbreak. All vortices initially developed offshore, subsequently making a landfall. The structure and temporal evolution of these vortices during the landfall were investigated using high-resolution data obtained from two X-band Doppler radars. The studied vortices developed along a low-level convergence line characterized by cyclonic horizontal shear, suggesting that horizontal shearing instability was responsible for the initial development of the vortices. A detailed investigation was performed on a vortex that passed within a close range (‹ 10 km) of both radars and almost directly over two surface observation stations. As this vortex approached the coast, it extended upward with time and eventually reached a height greater than half of the echo-top height of the parent snowband. During the landfall, the vortex core diameter contracted markedly and its peak tangential velocity and vertical vorticity increased at lower altitudes. Such a temporal change of low-level vortex was associated with an intensification of low-level convergence around the vortex and the convergence line. These facts suggest that the stretching of the low-level vortex was responsible for the low-level vortex contraction and increase in peak tangential velocity and vertical vorticity during the landfall.
This study shows the horizontal structure of climatology of thermospheric nocturnal winds at a height of approximately 250 km in the Asia-Oceania region for the first time using observations made with Fabry-Perot interferometers (FPIs; optical wavelength of 630.0 nm). The FPIs used in this study were located at Shigaraki (Japan, 34.8°N, 136.1°E), Chiang Mai (Thailand, 18.8°N, 98.9°E), Kototabang (Indonesia, 0.2°S, 100.3°E), and Darwin (Australia, 12.4°S, 131.0°E). The observation data underwent quality control that involved consideration of cloud information, wind speed value, and standard deviation of results obtained from synchronous fringe images; approximately 30 % of the observation data from all the four stations were deemed suitable for use. The nocturnal diurnal changes at Shigaraki according to the local solar time were generally consistent with changes in China at similar latitudes, although the amplitudes were slightly different. All four stations showed the continuous flow pattern of the nocturnal diurnal wind in each season. The Chiang Mai and Darwin stations observed seasonal/diurnal changes similar to those observed by stations at similar latitudes on the North and the South American continents. Although there were fewer samples for Chiang Mai, Kototabang, and Darwin in the rainy season compared to that for Shigaraki, the seasonal climatology reported here can be used to provide a background long-term average status for describing anomalous events and extremes having different causes.