SEASONAL DIFFERENCES IN THE LAND-ATMOSPHERE COUPLING OVER SOUTH ASIA SIMULATED USING A REGIONAL CLIMATE MODEL (original) (raw)
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Pure and Applied Geophysics, 2014
Influence of the land surface processes as an important mechanism in the development of the Indian Summer Monsoon is studied by performing simulations with a regional atmospheric model. Seasonal scale simulations are conducted for two contrasting summer monsoons (MJJAS months) in 2008 & 2009 with the Weather Research and Forecasting-Advanced Research regional model at a high resolution of 15 km using the boundary conditions derived from the National Centers for Environmental Prediction (NCEP) reanalysis data and using the NOAH land surface parameterization scheme. Simulations are evaluated by comparison of precipitation with 0.5°India Meteorological Department gridded rainfall data over land, atmospheric circulation fields with 1°resolution NCEP global final analysis, and surface fluxes with 0.75°resolution Era-Interim reanalysis. Results indicated significant variation in the evolution of the surface fluxes, air temperatures and flux convergence in the 2 contrasting years. A lower albedo, higher heating (sensible, latent heat fluxes), higher air temperatures, stronger flow and higher moisture flux convergence are noted over the subcontinent during the monsoon 2008 relative to the monsoon 2009. The simulated surface fluxes are in good comparison with observations. The stronger flow in 2008 is found to be associated with stronger heat flux gradients as well as stronger north-south geopotential/pressure gradients. The simulations revealed notable differences in many features such as zonal and meridional surface sensible heat gradients which, in turn, influenced the low-level pressure gradients, wind flow, and moisture transport. The present study reveals that, even at a regional scale, the physical processes of land-surface energy partitioning do influence the regional behavior of the monsoon system to a certain extent.
Contrasting regional and global climate simulations over South Asia
Climate Dynamics, 2020
Two ensembles of climate simulations, one global and one regional, are used to investigate model errors and projected climate change in seasonal mean temperature and precipitation over South Asia. The global ensemble includes ten global climate models (GCMs). In the regional ensemble all ten GCMs are downscaled by a regional climate model—RCA4 over South Asia at 50 km resolution. Our focus is on the Indian Summer Monsoon season (June–August) and we show that RCA4 can reproduce, reduce or amplify large-scale GCM biases depending on regions and GCMs. However, the RCA4 bias pattern in precipitation is similar across the simulations, regardless of forcing GCM, indicating a strong RCA4 imprint on the simulated precipitation. For climate change, the results indicate, that RCA4 can change the signal projected by the GCM ensemble and its individual members. There are a few RCA4 simulations with a substantial reduction of projected warming by RCA4 compared to the driving GCMs and with a larg...
International Journal of Global Warming, 2018
The ability of ICTP regional climate model version 4 (RegCM4.3) is investigated by using two land surface schemes: the biosphere-atmosphere transfer scheme (BATS) and the community land model version 3.5 (CLM3.5). To attain the best model configuration over the South Asia region, six sensitivity experiments are conducted with three different cumulus convection schemes. RegCM4.3 coupled with CLM3.5 and mixed convection scheme option (MIX-CLM), produced better simulation than BATS. The cold winter bias and the intensities of wet-dry biases over the foothills of Hindukush-Karakorum-Himalaya (HKH) and Central India are substantially reduced with MIX-CLM. In terms of seasonal variability, results suggest that different convection schemes behaved differently over sub-regions of the domain. The annual cycles of precipitation and temperature are better captured over the Bay of Bengal and Western Ghats by MIX-CLM. In spite of some deficiencies, the MIX-CLM scheme improves the model performance over the various parts of the domain.
Impact of modified soil thermal characteristic on the simulated monsoon climate over south Asia
Journal of Earth System Science, 2014
In the present study, the influence of soil thermal characteristics (STC) on the simulated monsoon climate over south Asia is analyzed. The study was motivated by a common warm temperature bias over the plains of northern India that has been noticed in several global and regional climate models. To address this warm bias and its relation to STC, two sensitivity experiments have been performed with the regional climate model REMO of the Max Planck Institute for Meteorology. The control experiment uses the standard soil thermal characteristic of the model that corresponds to a moist soil. The second experiment uses modified STC that characterize a dry soil, which is more representative of the considered region, as a large part of the region has arid, semi-arid or subtropical summer wet conditions. Both experiments were conducted over 20 years using re-analysis data as lateral boundary conditions. Results show that using the modified STC the predominant regional warm bias has reduced substantially, leading to a better and more realistic surface temperature compared to observations over south Asia. Although, the magnitude of bias has reduced, the warm bias still exists over the region suggesting that other atmospheric and land surface processes also play a role, such as aerosols and irrigation. These need to be addressed adequately in future modeling studies over the region.
Tokyo Metropolitan University, Tokyo, Japan, 2021
xx Precipitation during the Indian summer monsoon exhibits diurnal, intra-seasonal, and inter-annual variabilities. Among these variabilities, the diurnal convection cycle is the fundamental variability mode for tropical climates. In terms of the summer monsoon, this diurnal cycle of convection is an essential trigger that develops and organizes precipitation systems and contributes to the spatial and temporal distribution of monsoonal precipitation. The developmental features of these diurnal convection and precipitation systems are not well represented in global and regional climate models across different monsoon regions. Such uncertainty in the diurnal convection representation undermines the fundamental reliability of the simulated physical processes in the climate models. This has encouraged an examination into the unpredictability of the Indian monsoon diurnal convection in climate models; this has received little research attention in the past. Current research has focused on observations and modeling techniques to diagnose the observed diurnal convection cycle in a tropical monsoon and understand the importance of its representation in climate models. After simulating the diurnal cycle realistically in the regional climate model, we explored the sensitivity of diurnal precipitation characteristics to Indian land surface conditions over heterogeneous surfaces. This study begins with an observational understanding of the diurnal convection cycle in terms of precipitation and its characteristics during the summer monsoon. This is carried out using satellite observations from the 21-y (1998 2018) climatology of the Tropical Rainfall Measurement Mission (TRMM) 3B42 V7 dataset. The diurnal cycle
Influence of different land-surface processes on Indian summer monsoon circulation
Natural Hazards, 2007
The impact of different land-surface parameterisation schemes for the simulation of monsoon circulation during a normal monsoon year over India has been analysed. For this purpose, three land-surface parameterisation schemes, the NoaH, the Multi-layer soil model and the Pleim-Xiu were tested using the latest version of the regional model (MM5) of the Pennsylvania State University (PSU)/ National Center for Atmospheric Research (NCAR) over the Indian summer monsoon region. With respect to different land-surface parameterisation schemes, latent and sensible heat fluxes and rainfall were estimated over the Indian region. The sensitivity of some monsoon features, such as Somali jet, tropical easterly jet and mean sea level pressure, is discussed. Although some features of the Indian summer monsoon, such as wind and mean sea level pressure, were fairly well-simulated by all three schemes, many differences were seen in the simulation of the typical characteristics of the Indian summer monsoon. It was noticed from the results that the features of the Indian summer monsoon, such as strength of the low-level westerly jet, the cross-equatorial flow and the tropical easterly jet were better simulated by NoaH compared with verification analysis than other land-surface schemes. It was also observed that the distribution of precipitation over India during the peak period of monsoon (July) was better represented with the use of the NoaH scheme than by other schemes.
Role of Turbulent Heat Fluxes over Land in the Monsoon over East Asia
International Journal of Geosciences, 2011
Atmospheric heat and moisture over land are fundamental drivers of monsoon circulations. However, these drivers are less frequently considered in explaining the development and overall intensity of monsoons than heat and moisture over the ocean. In this study, the roles of turbulent heat fluxes over land in the monsoon system over East Asia are examined using Climatic Research Unit observations and European Centre for Medium-Range Weather Forecasts reanalysis, and they are further explored using simulated sensible (H) and latent (LE) heat fluxes from an ecosystem model (Predicting Ecosystem Goods and Services Using Scenarios or PEGASUS). Changes in the H fluxes over the land during the pre-monsoon season (March-May: MAM) affect the differential heating between land and ocean, which in turn controls monsoon development. In July, an intensified contrast of the mean sea level pressure between land and ocean is observed during the years of stronger land-sea H contrast in MAM, which results in enhanced onshore flows and more rainfall over southern East Asia. After monsoon onset, the contrast of H is influenced by monsoon rainfall through the cooling effect of precipitation on surface air temperature. During the monsoon season (June-September: JJAS), LE fluxes are more important than H fluxes, since LE fluxes over land and ocean affect overall monsoon intensity through changes in the land-sea contrast of turbulent heat fluxes. Significantly increased monsoon rainfall over western East Asia is observed during the years of larger LE over the land in JJAS. In ecosystem modeling, we find that the monsoon can be weakened as potential (natural) vegetation is converted to bare ground or irrigated cropland. Simulated H fluxes in MAM and LE fluxes in JJAS over the land significantly decrease in irrigated crop and bare ground scenarios, respectively, which play crucial roles in controlling monsoon development and overall intensity.
Climate modeling is a significant tool to reproduce the observed features of present climate changes and can provide reliable estimations for future climate changes at global and regional levels. In the present study we use latest version of International Center for Theoretical Physics (ICTP) regional climate model (RegCM4.3) to examine its ability by analyzing the European Community-Hamburg atmospheric model (ECHAM5) and the European Centre for Medium-Range Weather Forecast (ECMWF) 40 years reanalysis data (ERA-40) over South Asia. Seasonal mean climatology and annual cycle are compared with different observation based data sets and also with the reanalysis and driving GCM. Two experiments are conducted for present day simulation (1971-2000) by using ERA-40 reanalysis and ECHAM5 GCM to provide the initial and lateral boundary conditions. In spite of complex topography of the domain RegCM4.3 shows an improved performance in various aspects as compared to the earlier applications of this model over South Asia. Near surface air temperature are reproduced well over the most part of the domain. Indian monsoon precipitation patterns are better captured by RegCM4.3 as compared to the driving data set of ECHAM5 and ERA40. Simulation results show that RegCM4.3 has cold bias in winter and summer over the foothills of the Hindu-Kush-Himalaya (HKH) region. Simulation with ERA40 and ECHAM5 overestimated the seasonal mean precipitation over some part of the domain which requires further improvement in the physical parameterization scheme of RegCM4.3.
2002
Land-surface processes are an important driver for weather and climate systems over the tropics and particularly the Indian subcontinent. Realistic representation of landsurface processes over the Indian region will help accurate simulations of environmental processes at micro, meso, and regional climate scale. However, in order to achieve these potential benefits, it is necessary to develop a strategy through the Indo-US Forum on Science and Technology that will address and overcome the different challenges associated with the representation of the land-surface processes over the Indian region. In this review, seven focus areas are identified: (i) development of a highresolution surface data set for soil and vegetation /biophysical characteristics; (ii) testing of different biophysical Parametrizations in the land-surface schemes including ecological/ photosynthesis based land surface models at different scales; (iii) developing techniques to assimilate surface meteorological and land surface data in to regional analyses; (iv) development of regional climate studies to identify the radiative and other biogeophysical forcings that are critical to this region so as to include them in GCM studies; (v) studying the recirculation of evaporation, transpiration, and precipitation as part of the Indian monsoon system as well as effects of land atmosphere interactions on heavy precipitation and tropical storm track and intensity; (vi) assessing the effect of regional aerosols and soot on global climate through changes in land atmosphere interactions, cloudiness, and water vapor recirculation; and (vii) initiation of studies related to the inclusion of population growth and corresponding energy usage and land use change as a forcing within regional climate models.
Effect of convection schemes on the simulation of monsoon climates: A sensitivity study using RegCM4
Climate Research
To achieve the best climate simulation performance for a given area, the convection schemes of the area require examination. RegCM4, the latest version of a well-known regional climate model (RCM), was recently released with several improvements, including its representation of convection schemes. This new version employs 3 different convective schemes, and a major augmentation compared with previous versions of the model is its capability to simultaneously apply different convection schemes over the land and ocean, which is a configuration referred to as a mixed convection scheme. Here we tested all of the model-supplied convection schemes (version 4.1) in a 3 yr simulation. Model performances over East Asia (EA) and 4 sub-regions were evaluated. Our results showed that the 2 closure types in the Grell scheme produced different effects over EA, suggesting that the heating mechanism of buoyant energy is a key factor in this region. The Grell schemes, especially the Grell-AS scheme, tended to produce a dryer climate over the middle and lower reaches of the Yangtze River and southeastern China in the coarse resolution. Based on observations of the dynamics and microphysics of convection, the MIT scheme performed better than the often-employed idealization based on bulk-entraining plumes, but it tended to overestimate the water mixing ratio, leading to a wetter climate than the observations. The Kuo scheme showed relatively poor performance in the precipitation presentation in this region. Our results also showed that the mixed schemes can reduce the systematic cold bias of the model, and that the model performance can be significantly improved by increasing the model resolution.