We investigate the structure of a moist layer and sources of water in the southern region far from the Meiyu/Baiu front using GAME (GEWEX Asian Monsoon Experiment, GEWEX: Global Energy and Water Cycle Experiment) reanalysis data. In the period from July 4 to 15, 1998, the Meiyu/Baiu front was located over northern China (the Yellow River Valley) and the Korean Peninsula. Both regions over the plain area of mainland China (the eastern region of 112°E line) and the East China Sea have very moist air masses in this period; the total precipitable water over the regions is about 45 kgm−2. However, the structure of these moist layers is quite different. The moist layer over mainland China is deep, reaching 600 hPa. On the other hand, the moist layer over the East China Sea is shallow, with a thickness of up to 800 hPa. This difference in the structure of the moist layers can be attributed to the development of a moist convective mixing layer and the generation of shallow convective clouds in the daytime over mainland China, as a result of the supply of abundant latent and moderate sensible heat fluxes from the land surface. We also examine the sources of water supplied into the Meiyu front using Colored Moisture Analysis (CMA). Though water vapor to generate the deep moist layer over mainland China is mainly transported from the upstream regions of the Asian summer monsoon, which include the Indian Ocean, the Indochina Peninsula, and the South China Sea, the rate of the contribution of water from the southeastern region of mainland China is over 15% of the total precipitable water, when the Meiyu front is located over northern China. This shows that the land surface over southeastern China is regarded as a major source of water to the Meiyu front.
The most striking feature of the Asian-Australian monsoon associated with the El Niño teleconnection is the evolution of anomalous anticyclones over the western North Pacific (WNP) and southeast Indian Ocean (SIO). In this study we investigated the relative role of remote and local SST forcing in shaping the monsoon anomalies with an atmospheric general circulation model (AGCM). Four idealized AGCM experiments were designed to isolate the effect of anomalous SST forcing from the tropical eastern Pacific, tropical western Pacific and tropical Indian Ocean. In the first experiment observed SST is specified in the tropical eastern Pacific, while climatological monthly mean SST is specified elsewhere. In the second experiment the observed SST is specified in the tropical western Pacific only. In the third experiment realistic SST is specified in both the tropical Indian Ocean and eastern Pacific. In the fourth experiment the observed SST is specified across the tropical Indian and Pacific Oceans. Our numerical experiments indicate that the anomalous anticyclone in the WNP is initiated by local SST anomaly (SSTA) forcing in northern fall, and further maintained by both the remote (El Niño) and local SSTA forcing. The initiation of the anomalous anticyclone over the SIO is primarily attributed to the local SSTA, though the remote forcing from the eastern Pacific also plays a role, particularly in 1997. The numerical experiments reveal a seasonal-dependent character of inter-basin teleconnection between the tropical Pacific and Indian Oceans, this is, the Indian Ocean SSTA exerts a significant impact on the western Pacific wind in northern summer and fall of the El Niño developing year, whereas the eastern Pacific SSTA has a greater impact on the Indian Ocean wind during the mature phase of the El Niño (boreal winter), even though the central Pacific heating is stronger in boreal summer. A special feature for 1997-98 El Niño is that the meridional wind anomaly over the Indian Ocean in DJF is primarily driven by local SSTA forcing, while the zonal wind component is forced by the remote SSTA in the eastern Pacific.
In this study, we evaluate the performance of global climate models for reproducing the present SLP (sea level pressure) field in the CO2 transient run, which will be used for the prediction of regional climate change. The outputs calculated using the model are projected in ‘PC-space’, with the component scores from the principal components (or EOF) of observed data as the axes, and their biases are evaluated quantitatively. This evaluation method was applied to the previous runs (CSM125 and ACACIA) using NCAR-CSM. In the ACACIA run, the January SLP field is reproduced realistically and is improved from CSM125, although the winter monsoon is still weak. The reproduced pattern resembled that of December. On the other hand, the July SLP field is not reproduced well; the intensity of the North Pacific High is over estimated and its ridge is shifted to the north, which are both beyond the observed range. Through these analyses, the difference of bias pattern for each year between two runs which have similar mean distribution pattern is evaluated quantitatively. Then the performances of the models are compared quantitatively to the other global climate models in the world through the application of this method. All the models tend to reproduce the Siberian High weakly, which is a common feature of the present models. For the summer SLP field, all the models show poor performance as well as two NCAR runs. A series of analyses revealed that, outputs from two NCAR runs in winter seem to be usable, with some care, for the prediction of regional climate changes. However, summer results are insuflicient for such use, determined from the viewpoint of the performance of reproducing the present SLP field.
Russian research aircraft observed the atmospheric boundary layer in 2001 during weak (29 Jan.), intense (2 Feb.) and very intense (3 Feb.) cold air outbreaks. These observations occurred during a field experiment of Winter Meso-scale convective systems Observations, over the Sea of Japan in 2001 (WMO-0l). Conditional sampling techniques were used to elucidate air-mass modification processes upstream of the Sea of Japan during cold-air outbreaks. Buoyancy fluxes in the lower boundary layer near the sea surface differed significantly among the three cases. TKE budgets suggest that the differences were characterized mainly by differences in buoyancy production. However, common properties in heat transfer did exist, namely intensity (3.0) and fractional coverage (28%) of rising thermals (w+Tv+). Scale analysis showed that heating by convective-scale motions dominated in the lower boundary layer. Heating by meso-γ scale motions became more important in the upper boundary layer. Near the cloud top, on the other hand, contributions by cold downdrafts (w−Tv−) to the total buoyancy flux (w´Tv&actute;) dominated. Thecloud-top w´Tv´ was about half of that near the sea surface, suggesting that cooling processes near the cloud top are also important in TKE production. Comparisons of fractional spatial coverage of w+Tv+ with thermal motions over other warm oceans show good agreement with the AMTEX and GALE cases. However, flux intensities in the present case, and in the GALE case, are stronger than in the AMTEX case. Impacts on ocean convection by the upstream, large surface heat fluxes are discussed.
A scheme for the assimilation of radiance data from the Advanced TIROS Operational Vertical Sounder (ATOVS) into the global three-dimensional variational (3DVar) analysis system at the Japan Meteorological Agency (JMA) is described. It makes better use of ATOVS observations than the previous ATOVS retrieval assimilation scheme. Several procedures have been developed: advanced thinning, identification of cloud/rain-affected radiances, removal of radiance data which are erroneous or not well simulated with a current fast radiative transfer model and/or numerical weather prediction (NWP) model, selection of adequate channels and assignment of observation errors for different observation conditions, such as clear/cloud/rain and surface type, and correction of radiance biases in which the effects of NWP model biases are minimized. It was found from parallel experiments that the radiance assimilation shows significant improvement over the retrieval assimilation in many respects. Analyzed temperature and water vapor are improved when verified against radiosonde and the Special Sensor Microwave/Imager (SSM/I) observations. Impacts on forecasts are positive on the globe, especially for short-range forecasts. The reduction in the root mean square errors by the radiance assimilation reaches up to 0.5 K for the analyzed temperature against RAOBs, and about 5-10% for the 500 hPa geopotential height at day 1 to day 4 forecast. As a result of these findings, the ATOVS radiance assimilation was operationally implemented in the JMA global analysis system on 28 May 2003.
A sub-synoptic-scale depression, with a wavelengtJh of 2000-3000 km, propagated along the Meiyu-Baiu frontal zone from China to Northwestern Pacific during 03-05 July 1991. We investigated the development and change in the structure of the frontal depression in detail, by using the Geostationary Meteorological Satellite (GMS) Infrared (IR) and objective global analysis (GANAL) data, of the Japan Meteorological Agency. This sub-synoptic-scale depression develops in association with low/middle-level vorticity maxima and meso-x-scale cloud systems. However, the simple one-to-one correspondence among them is not lasting for the whole life time of the depression, but the multiple coupling among the depression, vorticity cores and cloud systems occurs during the evolution process. The vertical structure of the depression varies in accordance with the low-level and middle-level vorticity cores, indicating the differentmovement and evolution in the coupling process. The present study thus demonstrates an example of multi-scale interactions related to the complicated evolution process of the sub-synoptic-scale depression on the Baiu frontal zone.
Based on Historical Soviet Daily Snow Depth (HSDSD-II) data for the period 1941-1995, it is found that winter/spring snow depth anomalies over east Eurasia (70 E-160 E, 35 N-65 N) is positively correlated, while west Eurasia (25 E-70 E, 35 N-65 N) is negatively correlated with subsequent Indian summer monsoon rainfall (ISMR). The correlations become stronger and negative with winter snow depth anomaly over west Eurasia during the recent period of study (1975-1995). Four years of high snow (1966, 1968, 1979 and 1986) and two years of low snow (1961 and 1975) are selected on the basis of standardized winter snow depth anomaly over west Eurasia. The Pentad (Fivedays average) analysis of snow depth during the above contrasting snow years show that high/low snow is associated with late/early snow disappearance. NCEP/NCAR reanalyzed data are used for the study of some important atmospheric characteristics of seasonal monsoon circulation during high/low snow years, followed by deficient/excess ISMR. The important findings ofthis study are: (1) the anomalous persistence of winter/spring snow delays the spring time continental heating, results in weak thermal low and weak monsoon westerlies over India, (2) the difference fields of Velocity Potential shows complete phase reversal in the dipole structure from high to low snow years and (3) the temperature and related circulation fields show that low level jet over east Asia is also considerably influenced by Eurasian snow anomaly.
Regional variability in the carbon-cycle response of terrestrial ecosystems to global warming was simulated with a spatially explicit, process-based model (Sim-CYCLE), and analyzed for 22 regions worldwide. The terrestrial net flux ofcarbon dioxide (CO2) during the period 2001-2099, was globally simulated on the basis of greenhouse gas emission scenarios (IPCC-SRES), and climate projections by coupled atmosphere-ocean general circulation models (AOGCMs). Most terrestrial ecosystems acted as net carbon sinks but with different magnitudes among the experiments (globally, 24 to 286 Pg C). Substantial inter-regional variability was found in terrestrial carbon-cycle response, because of differences in biome distributions and climate-change regimes. Moreover, among the experiments using the same CO2 scenario, but different AOGCM climate projections, inconsistent results were obtained in the Amazon basin, Africa, Australia and northern Asia, indicating the need for further research.
Influence of springtime surface condition over Siberia upon subsequent summertime blocking activity over northeastern Siberia, and the Okhotsk sea is examined. It is found that when the surface temperature over Siberia is high in April (the high years), blocking events over northeastern Siberia, and the Okhotsk sea in May and June occur more frequently than climatology. In the high years, a jet stream over the north of Siberia is formed in the upper troposphere, corresponding to the enhanced meridional temperature gradient, and the polar frontaljet is observed from April to the beginning of July over East Asia. During this period, the meridional gradient of potential vorticity is more gradual, between this high-latitude jet stream and a subtropical jet, consistent with the more frequent occurrences of blocking. Associated with the enhancement of blocking activity, is the intensification of the surface Okhotsk high and cold anomaly to its south over the northern part of Japan during the early summer season of the high years. The finding of this study suggests monitoring the springtime surface condition over northern Siberia as one of the promising predictors for the early-summer climate over East Asia.