The new simulation of Martian general circulation based on CCSR/NIES AGCM has been performed and the numerical results analyzed. We attempt to reproduce the atmospheric states of Mars which havebeen observed by the Mars Global Surveyor, and Viking by introducing three kinds of time- and latitude- dependent dust opacity scenarios which are made to be consistent with the past observational results, as the observed dust distribution during spring and summer in south hemisphere varies largely at eachyear and so does observed atmospheric conditions. The model with TES2 dust scenario, which is the dustdistribution based on the observation by the Mars Global Surveyor in 1999, generally reproduces distributions of temperature and zonal wind observed by the Mars Global Surveyor in 1999, though the temperature tends to be lower at high altitude. The maximum value of CO2 ice thickness at polar regions relatively reproduces the observation, but the edge of the northern and southern seasonal caps are outside of the observational results during spring, which results in lower surface pressure especially in northern spring. Annual variations of the amplitudes of the diurnal and semidiurnal tide are qualitatively comparable between our model with VIK1 dust scenario, which is the dust distribution based on the observation by Viking Orbiter in 1977, and observation by Viking Lander 1 in 1977. The baroclinic waves with consistent periods, wavenumbers and phase speeds with observational results by Viking Lander 2 in 1977 are reproduced in the autumn, though in the winter, during the second dust storm, and in the spring, the phase speeds are faster than observation.
Radar data from the Bangladesh Meteorological Department (BMD) are employed as a preliminary analysis. This is a first research work to investigate the spatial and temporal distribution of rainfall over the country for 135 consecutive days, from 16 April to 30 August 2000. Radar data are sampled in 10 km grid boxes to obtain daily rainfall over the country. Rain gauge data at 33 locations are utilized to check the radar results. The distributions of rainfall obtained by both the radar and the rain gauges are similarin pattern, but the time of the maximum rainfall determined by the radar is a few hours earlier than that determined by the rain gauges. The distribution of rainfall over the whole radar domain suggests that 21 to 09 local standard time (LST) is the most likely time for rainfall to occur in Bangladesh, while 06 LST is the most likely time for maximum rainfall to occur over the entire country. It is mentioned that no data are available between 03-06 LST. The occurrence of 21 to 09 LST rainfall is possibly linked to the local effects such as complex terrain and sea and land breeze circulations. The morning maximum rainfall at 06 LST in Bangladesh is different from that of the Indian subcontinent or of the mountain area where, generally, maximum rainfall occurs in the afternoon. The northern border of Bangladesh, close to the Shillong hill of India, is the region with the highest rainfall, while the second highest volume of rainfall occurs on the eastern border. In order to observe the characteristics of large-scale cloud activity, analyses of the Japanese GMS-5 hourly infrared data, within a larger domain of 80°-100°E and 10-30°N were conducted. The cloud activities in and around Bangladesh were obtained in 10 by 10 grid boxes. The northwestern part of Bangladesh was largely affected by pre-monsoon clouds, while the whole country was affected by the peak monsoon activities.
A method has recently been shown by Aoki (2004) to compress the number of channels of trace gas remote sounder preserving almost all the information content that the original data has. In this method the weighting function of the original channels is expanded with empirical orthogonal functions (EOFs), and a set of hypothetical radiances, whose weighting functions are the EOFs, are used for the analysis. It has been shown that the radiance data of 240 original channels, which is obtained by the above trace gas sounder, can be compressed to 3 or less channels of hypothetical radiances, loosing negligible information content. In the present paper, the performance of this method is examined for the simulated radiance data of high spectral resolution in the thermal infrared region that is used for the remote measurements of temperature and humidity vertical profiles. The number of hypothetical channels that is required for preserving the information content of original data has been examined for two different spectral resolutions, 0.1 and 0.3 cm−1. The present study showed that the radiance data of 1200 channels of high spectral resolution 0.1 cm−1 is compressed to less than 23 hypothetical channels with negligible loss of information content in the case of wavenumber region 640-760 cm−1, which is used for the temperature soundings. For the low resolution 0.3 cm−1, the number of hypothetical channels needed becomes smaller than this. In the case of the humidity sounding from the region 1300-1600 cm−1 with the spectral resolution 0.1 cm−1, 3000 channels are compressed to less than 20 hypothetical channels.
Over the subtropical northwestern Pacific, a prominent ozone minimum of less than 235 Dobson Units (DU) is observed in winter, with extremely low values of less than 200 DU occurring occasionally over this region for short time periods (days to weeks). In this study the vertical structure of this ozone minimum is examined using a 9 year (1991-2000) average of the total ozone mapping spectrometer (TOMS) and Halogen Occultation Experiment (HALOE) data. It is found that the ozone minimum is mainly stratospheric origin with two distinct low-ozone layers in the stratosphere, one in the middle stratosphere of 10-15 hPa, and the other in the lower stratosphere of 40-60 hPa. The mid-stratospheric low-ozone layer is attributed to southward transport of high-latitude low-ozone air by atmospheric circulation in wintertime associated with the Aleutian High, which is simulated successfu11y using a simple chemical transport model. The extremely low ozone was observed in December 2001 over the subtropical northwestern Pacific. This case is also examined by ozonesonde observations at Naha (26°12´N, 127°41´E) and the model. Both the results from the 9 year climatological field, and the December 2001 field, show that the wintertime total ozone minimum over the subtropical northwestern Pacific is substantially dynamical in origin.
Observation data and output of a regional climate model, RegCM2.5, nested in a global climate model, NCAR-CSM, were analyzed to determine the standard deviation and frequency of extreme values, which were used as indices to characterize the variability of the daily minimum (Tmin) and maximum (Tmax) temperatures in Japan. The frequency of extreme values, which are defined in this paper as deviations greater than twofold the standard deviation, was estimated from data using a new method. The significant results of this analysis of observation data are as follows. With regards to both Tmin andTmax, the significant seasonal variations of standard deviation are the annual and semiannual ones, with the minimum value in August and a weak minimum in January. The region where the standard deviation is large drifts northward from February to May, with a maximum standard deviation in Apri1. The central latitude almost agrees with that where the zonal wind is maximum at 500 hPa. As compared with the normal distribution, the extremely high temperature in summer, and the extremely low temperature in winter, are observed less frequently. The indices calculated from the model's output after simulating the current climatic condition were compared with the observation data for evaluation. From this comparison, it is shown that the variability characteristic of Tmax was not reproduced well; however, that of Tmin was reproduced well by the model. Therefore, it is concluded that Tmin. reproduced by RegCM/CSM can be used to predict the change in the frequency of extreme values by correcting the systematic temperature bias, which is within ±1 K.
The rainfall phenomena in the pre-monsoon season over the Indochina Peninsula are investigated using geopotential height, wind and moisture fields by the NCEP/NCAR reanalysis, and OLR, precipitation and GPS data during the GAME-IOP year, 1998. In early and middle April, and early May, the lower OLR regions, which represent the heavy convective activity, extend southward from the mid-latitude zone to the Indochina Peninsula, bringing intermittent rainfall events in a wide region over the central part ofthe peninsula. The composite analysis in these three rainfall events shows that they are brought by the trough passage in the upper troposphere, which migrates eastward in the middlel atitude westerlies along the southern periphery of the Tibetan Plateau. The lower tropospheric moisture inflow in these rainfall events is found to come mainly from the south and east, which shows sharp contast with the situations of inflow mainly from the west, during the non-precipitation days in the premonsoon season, and the rainfall situations after the monsoon onset in middle May.
Interannual variation of seasonal changes of precipitation and moisture transport in the western North Pacific from June to August is studied using global monthly precipitation data, and NCEP-NCAR (National Center for Environmental Prediction-National Center for Atmospheric Research) reanalysis for 20 years from 1979 to 1998. According to the meridional shift of the intense precipitation area and precipitation amounts in June and August to the east of the Philippines, the seasonal changes of precipitation are categorized into Types A and B. Type A is characterized by the northward shift of intense precipitation area and the increase of precipitation from June to August. Type A is further classified into two: Sub-Types Al and A2. The former is characterized by the gradual increase of precipitation and the northward shift of the intense precipitation area from 6°N to 16°N. The latter is characterized by a relatively intense precipitation in June, decrease of precipitation in July, significant increase of precipitation with a maximum in August, and the northward shift from 13°N to 22°N. Type B is characterized by a seasonal change, with almost no precipitation increase nor northward shift from June to August. Difference in the precipitation amount between Types A and B corresponds to the westerly moisture flux originating from the Indian Ocean, and the southerly moisture flux which comes across the equator at the lower level. It is found that the westerly and southerly moisture flux in Type B are much smaller than those in Type A, especially in August. The westerly moisture flux in Sub-Type A2 is larger than that in Sub-Type Al. The seasonal changes ofwesterly moisture flux show gradual increase in Sub-Type Al, and significant increase in June and August and decrease in July in Sub-Type A2. They are corresponding to those of the precipitation amount, respectively. The large westerly moisture flux and the strong moisture convergence to the east of the Philippines in August in Type A, are associated with the eastward extension of the trough from the Eurasian continent. The northward shift of the intense precipitation area corresponds to the intensification of the eastward extended trough.
When a basic flow with linear or axial symmetry has a region of negative potential vonicity (hereafter PV), such a disturbance with the same symmetry as the basic flow grows that converts the negative PV of the region into non-negative PV. This is the so-called symmetric instability. In this note, the following is shown in a nondissipative adiabatic system. Irrespective of the symmetry, disturbances grow in the region of negative PV. That is, irrespective of the symmetry, a flow with negative PV is unstable. This statement is based on the conservation law of absolute circulation around a material closed curve on the isentropic surface.