Simulation sensitivities of the major weather regi

Authors: Chainarong Raktham Cindy Bruyère Jiemjai Kreasuwun James Done Chitrlada Thongbai Wonchai Promnopas

Publish Date: 2014/05/22

Volume: 44, Issue: 5-6, Pages: 1403-1417

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Abstract

This study evaluates the Weather Research and Forecasting model’s ability to simulate major weather phenomena dry conditions tropical cyclones TCs and monsoonal flow over East and Southeast Asia Sensitivity tests comprising different cumulus Kain–Fritsch and Betts–Miller–Janjic and microphysics Purdue Lin WSM3 WSM6 and Thompson are used together with different placement of lateral boundaries to understand and identify suitable model configuration for weather and climate simulations over the Asia region All simulations are driven with reanalysis data and use a nominal grid spacing of 36 km with 51 levels in the vertical The dry season showed little sensitivity to any configuration choices while the TC case shows high sensitivity to the cumulus scheme and low sensitivity to the microphysical scheme Monsoon simulations displayed significant sensitivity to the placement of the lateral boundariesTropical cyclones TCs are responsible for exchanging energy between oceans and the atmosphere and between the low and high latitudes releasing enormous amounts of latent heat TCs are also thought to play a large role in driving the global and regional water cycle by enhancing lowlevel convergence that supply the free troposphere with an upward flux of unstable air which in turn brings moisture from the ocean to the land Raymond 1995 In some cases TCs can bring severe weather events like flashfloods landslides and storm surgeThailand in Southeast Asia is affected by TCs both directly and indirectly In 2005 tropical storm Vicente made landfall on the Indochina peninsula from the South China Sea SCS Cabinet resolution Thailand Cabinet resolution 2005 reports that the storm killed 4 people injured several and severely affected more than 150000 The storm affected 16 provinces throughout Thailand washed away roads and bridges closed schools and caused severe damage to more than 100000 acres of agricultural land Vicente originated over the Northwest Pacific Ocean and moved westward across the Philippines before making landfall Raktham et al 2007 In 2004 Typhoon Chantu also a Pacific storm with a westward track made landfall in Vietnam and caused deadly flooding in Vietnam Laos and Thailand and caused substantial changes in river levels Wangwongchai et al 2010 These westward tracking storms are recognized as causing high impacts in East and Southeast Asia Harr and Elsberry 1991 Guo et al 2012There is evidence that TCs are affected by climate change Knutson et al 2010 Webster et al 2005 showed that over the last 30 years there has been a trend toward a larger proportion of the most intense TCs over most ocean basins including the Northwest Pacific Holland and Bruyère 2013 reported a strong link between the anthropogenic signal and the proportion of intense hurricanes that form in any given basin Stowasser et al 2007 indicates a continued trend towards higher proportion of the most intense TCs under future warming scenarios Shibin and Bin 2013 found that the recent increase of TC numbers in the West North Pacific in May is the result of an enhanced summer monsoon over the South Asia and SCSIn Taiwan TCs alone contribute nearly 50  of the total annual precipitation Chen et al 2010 so future changes in TC rainfall as suggested by Knutson et al 2010 may have important consequences for the region eg Chotamonsak et al 2011 Indeed a summary of six modeling studies reported model consensus of a future increase in rainfall rates over the Northwest Pacific basin Ying et al 2012Thailand is also influenced by the Southwesterly monsoon a subcomponent in the East Asian Summer Monsoon EASM Tao and Chen 1987 The EASM in turn sometimes interacts with Indian Summer Monsoon which can lead to anomalies in the monsoonal rainfall patterns over this area Wei et al 2013 As defined by Ramage 1971 EASM starts to flow through South East Asia during early May and affects Thailand from mid May Wang and Lin 2002 Monthly precipitation over the Thailand region is significantly enhanced during the monsoon season May through October Ding and Chan 2005Due to the large impact TCs and the EASM have on the East and Southeast Asia region it is important to study their potential changes under future climate change projections in order to understand the possible impact these changes will impose in terms of precipitation especially heavy precipitation and flood events The Weather Research and Forecasting WRF model Skamarock et al 2008 is a flexible and powerful tool to simulate and understand TC and monsoon climatology specifically since this limited area model enables far higher resolution simulation over a region of interest than is possible using a global climate model The WRF model has already been used successfully to study TC activity under climate change scenarios Done et al 2012 2013 Regional climate simulations can be very sensitive to aspects of model setup such as domain size and model physics and this sensitivity can vary by geographic region and season Rosenthal 1971 Solomon et al 2007 Gentry and Lackmann 2010 It is therefore critical to understand sensitivities of the modeling system for simulation of TCs and EASM prior to embarking on a climate change studyIn this paper we explore the sensitivity of WRF version 331 model simulations in East and Southeast Asia to aspects of model design and understand the importance of domain size and model physics parameterizations In Sect 2 we present the experimental design Section 3 presents results of the sensitivity studies and we conclude the paper with a discussion in Sect 4

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