The Influence of an SST Front on a Heavy Rainfall Event over Coastal Taiwan during TiMREX

2014 ◽  
Vol 71 (9) ◽  
pp. 3223-3249 ◽  
Author(s):  
Michael D. Toy ◽  
Richard H. Johnson
Keyword(s):  
Northern South China Sea ◽  
Wrf Model ◽  
Early Summer ◽  
Rainfall Event ◽  
Precipitation Event ◽  
Heavy Rainfall Event ◽  
Low Level ◽  
Sst Front ◽  
Southwest Coast ◽  
Sst Gradient

Abstract A long-lived heavy precipitation area was observed along the southwest coast of Taiwan from 13 to 18 June 2008 during the Terrain-Influenced Monsoon Rainfall Experiment (TiMREX). Rainfall amounts exceeded 500 mm along portions of the coast, and the coastal plains experienced severe flooding. The precipitation systems were influenced by blocking effects, as the southerly moist monsoon flow impinged on the island. A relatively strong gradient in the sea surface temperature (SST) off the southwest coast of Taiwan existed during the rainfall event. Mesoscale SST fronts are known to influence the planetary boundary layer (PBL) such that low-level convergence and precipitation are enhanced under certain circumstances. In this study, the authors investigate the role of the SST front in enhancing the 13–18 June 2008 precipitation event over Taiwan using the Weather Research and Forecasting (WRF) Model. In control simulations with the observed SST, there is a transition from a well-mixed to a stable PBL across the front, causing the low-level flow to decelerate, resulting in an enhancement of horizontal convergence. Such a transition in the PBL and the associated convergence is greatly reduced in smoothed SST gradient model simulations, which produce over 20% less precipitation over southwest Taiwan. Sensitivity tests show that, qualitatively, the results are independent of the existence of the island of Taiwan. These findings indicate that the SST gradient over the northern South China Sea during the early summer monsoon can have a significant impact on the intensity of rainfall over Taiwan.

scholarly journals NUMERICAL SENSITIVITY EXPERIMENTS ON PRECIPITATION IN A HEAVY RAINFALL EVENT SIMULATED BY USING THE WRF MODEL

2014 ◽  
Vol 70 (4) ◽  
pp. I_541-I_546 ◽  
Author(s):  
Yuji SUGIHARA ◽  
Sho IMAGAMA ◽  
Yohei OHKUMA ◽  
Nobuhiro MATSUNAGA ◽  
Yukiko HISADA ◽  
...  
Keyword(s):  
Heavy Rainfall ◽  
Wrf Model ◽  
Rainfall Event ◽  
Heavy Rainfall Event ◽  
Sensitivity Experiments

scholarly journals Evaluation of Two Cloud-Resolving Models Using Bin or Bulk Microphysics Representation for the HyMeX-IOP7a Heavy Precipitation Event

Atmosphere ◽  
2020 ◽  
Vol 11 (11) ◽  
pp. 1177
Author(s):  
Diana Arteaga ◽  
Céline Planche ◽  
Christina Kagkara ◽  
Wolfram Wobrock ◽  
Sandra Banson ◽  
...  
Keyword(s):  
Hydrological Cycle ◽  
Wrf Model ◽  
Heavy Precipitation ◽  
Sensitivity Study ◽  
Precipitation Event ◽  
Convective System ◽  
Wind Fields ◽  
Massif Central ◽  
Surface Precipitation ◽  
Low Level

The Mediterranean region is frequently affected in autumn by heavy precipitation that causes flash-floods or landslides leading to important material damage and casualties. Within the framework of the international HyMeX program (HYdrological cycle in Mediterranean EXperiment), this study aims to evaluate the capabilities of two models, WRF (Weather Research and Forecasting) and DESCAM (DEtailed SCAvenging Model), which use two different representations of the microphysics to reproduce the observed atmospheric properties (thermodynamics, wind fields, radar reflectivities and precipitation features) of the HyMeX-IOP7a intense precipitating event (26 September 2012). The DESCAM model, which uses a bin resolved representation of the microphysics, shows results comparable to the observations for the precipitation field at the surface. On the contrary, the simulations made with the WRF model using a bulk representation of the microphysics (either the Thompson scheme or the Morrison scheme), commonly employed in NWP models, reproduce neither the intensity nor the distribution of the observed precipitation—the rain amount is overestimated and the most intense cell is shifted to the East. The different simulation results show that the divergence in the surface precipitation features seems to be due to different mechanisms involved in the onset of the precipitating system: the convective system is triggered by the topography of the Cévennes mountains (i.e., south-eastern part of the Massif Central) in DESCAM and by a low-level flux convergence in WRF. A sensitivity study indicates that the microphysics properties have impacted the thermodynamics and dynamics fields inducing the low-level wind convergence simulated with WRF for this HyMeX event.

scholarly journals The Role of Typhoon Songda (2004) in Producing Distantly Located Heavy Rainfall in Japan*

2009 ◽  
Vol 137 (11) ◽  
pp. 3699-3716 ◽  
Author(s):  
Yongqing Wang ◽  
Yuqing Wang ◽  
Hironori Fudeyasu
Keyword(s):  
Heavy Rainfall ◽  
Control Experiment ◽  
Wrf Model ◽  
Heavy Precipitation ◽  
Precipitation Event ◽  
Initial Time ◽  
Heavy Rainfall Event ◽  
Arw Model ◽  
Southern Central ◽  
Environmental Prediction

Abstract When Typhoon Songda (2004) was located southeast of Okinawa over the western North Pacific during 2–4 September 2004, a heavy rainfall event occurred over southern central Japan and its adjacent seas, more than 1200 km from the typhoon center. The Advanced Research version of the Weather Research and Forecast (WRF-ARW) model was used to investigate the possible remote effects of Typhoon Songda on this heavy precipitation event in Japan. The National Centers for Environmental Prediction (NCEP) global final (FNL) analysis was used to provide both the initial and lateral boundary conditions for the WRF model. The model was initialized at 1800 UTC 2 September and integrated until 1800 UTC 6 September 2004, during which Songda was a supertyphoon. Two primary numerical experiments were performed. In the control experiment, a bogus vortex was inserted into the FNL analysis to enhance the initial storm intensity such that the model typhoon had an intensity that was similar to that observed at the initial time. In the no-typhoon experiment, the vortex associated with Typhoon Songda in the FNL analysis was removed by a smoothing algorithm such that the typhoon signal did not appear at the initial time. As verified against various observations, the control experiment captured reasonably well the evolution of the storm and the spatial distribution and evolution of the precipitation, whereas the remote precipitation in Japan was largely suppressed in the no-typhoon experiment, indicting the significant far-reaching effects of Typhoon Songda. Songda enhanced the remote precipitation in Japan mainly through northward moisture transport into the preconditioned precipitation region by its outer circulation. The orographic forcing of the central mountains in Japan played a small role compared with Typhoon Songda in this extreme precipitation event.

scholarly journals Convection Initiation and Growth at the Coast of South China. Part I: Effect of the Marine Boundary Layer Jet

2020 ◽  
Vol 148 (9) ◽  
pp. 3847-3869 ◽  
Author(s):  
Yu Du ◽  
Guixing Chen ◽  
Bin Han ◽  
Chuying Mai ◽  
Lanqiang Bai ◽  
...  
Keyword(s):  
Boundary Layer ◽  
South China ◽  
Marine Boundary Layer ◽  
Rapid Development ◽  
Northern South China Sea ◽  
Heavy Rainfall Event ◽  
Inertial Oscillation ◽  
Low Level ◽  
Convergence Zones ◽  
Convection Initiation

Abstract Convection initiation (CI) and the subsequent upscale convective growth (UCG) at the coast of South China in a warm-sector heavy rainfall event are shown to be closely linked to a varying marine boundary layer jet (MBLJ) over the northern South China Sea (NSCS). To elucidate the dynamic and thermodynamic roles of the MBLJ in CI and UCG, we conducted and analyzed convection-permitting numerical simulations and observations. Compared to radar observations, the simulations captured CI locations and the following southwest–northeast-oriented convection development. The nocturnal MBLJ peaks at 950 hPa and significantly intensifies with turning from southwesterly to nearly southerly by inertial oscillation. The strengthened MBLJ promotes mesoscale ascent on its northwestern edge and terminus where enhanced convergence zones occur. Located directly downstream of the MBLJ, the coastal CI and UCG are dynamically supported by mesoscale ascent. From a thermodynamic perspective, a warm moist tongue over the NSCS is strengthened by the MBLJ-driven mesoscale ascent as well as by a high sea surface temperature. The warm moist tongue farther extends northeastward by horizontal transport and arrives at the coast where CI and UCG occur. Near the CI location, rapid development of a low-level saturated layer is mainly attributed to the mesoscale ascent and low-level moistening associated with the MBLJ. In addition, subsequent CI happens on either side of the original CI along the coast due to the delay of low-level moistening, which partly contributes to linear convective growth. Furthermore, ensemble simulations confirmed that a stronger MBLJ is more favorable to CI and UCG near the coast.

Numerical Experiments on Spatially Averaged Precipitation in Heavy Rainfall Event Using the WRF Model

2015 ◽  
Vol 10 (3) ◽  
pp. 436-447 ◽  
Author(s):  
Yuji Sugihara ◽  
◽  
Sho Imagama ◽  
Nobuhiro Matsunaga ◽  
Yukiko Hisada ◽  
...  
Keyword(s):  
Numerical Experiments ◽  
Heavy Rainfall ◽  
Wrf Model ◽  
Analysis Data ◽  
Rainfall Event ◽  
Weather Research And Forecasting ◽  
Heavy Rainfall Event ◽  
Spatial Averaging ◽  
Hourly Rainfall ◽  
Precipitation Analysis

It is difficult to forecast hourly rainfall locally even using the latest meteorological models, although hourly rainfall averaged spatially to some extent can be used for calculating practical rainfall. This study conducts numerical experiments with triple nesting on the 2012 heavy rainfall event in northern Kyushu using the weather research and forecasting (WRF) model and examines the features of hourly rainfall averaged spatially. The dependence of rainfall is averaged spatially on a spatial averaging scale and clarified by comparing rainfall calculated by simulation using the WRF model with radar/AMeDAS precipitation analysis data. This study’s findings indicate the effective spatial averaging scale making relative error of calculated values to the observed ones minimum.

scholarly journals Numerical Study of the Rainfall Event due to the Interaction of Typhoon Babs (1998) and the Northeasterly Monsoon

2009 ◽  
Vol 137 (7) ◽  
pp. 2049-2064 ◽  
Author(s):  
Chun-Chieh Wu ◽  
Kevin K. W. Cheung ◽  
Ya-Yin Lo
Keyword(s):  
Heavy Rainfall ◽  
Cold Front ◽  
The Philippines ◽  
Rainfall Event ◽  
Heavy Rainfall Event ◽  
Rainfall Distribution ◽  
Low Level ◽  
Sensitivity Experiments ◽  
Control Simulation ◽  
Monsoon Strength

A heavy rainfall event in the Taiwan area associated with the interaction between Typhoon Babs (1998) and the East Asia winter monsoon is studied. Typhoon Babs is a case in point demonstrating the often-observed phenomenon that heavy rainfall can be induced in the eastern and/or northeastern region of Taiwan. Such heavy rainfall was caused by the joint convergent flow associated with the outer circulation of typhoons and the strengthening northeasterly monsoon in late typhoon season, even though Babs remained distant from Taiwan when it moved through the island of Luzon in the Philippines and stayed over the South China Sea. This heavy rainfall event is simulated in this study using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) with three nested domains and a highest horizontal resolution of 6.67 km. The control experiments with Kain–Fritsch cumulus parameterization perform well in terms of both simulated track and intensity. The 20-km resolution simulation reproduces the correct rainfall distribution during the three days studied, and the fine domain with 6.67-km resolution further improves the maximum simulated rainfall to very close to the observations. A series of sensitivity experiments that include model physics, terrain effect, typhoon vortex structure, and monsoon strength is performed, aiming at investigating the predictability of this typhoon–monsoon–terrain system when some of its components are perturbed. The rainfall event is analyzed based on two rainfall modes of different dominant mechanisms: monsoon mode during 0000 UTC 24–25 October and topographic mode during 0000 UTC 25–26 October. Removal of the Taiwan terrain in one of the sensitivity experiments results in completely different rainfall distribution due to the lack of the convection by orographic lifting, and the terrain is also found to play a key role in changing the low-level convergence pattern between the typhoon circulation and monsoonal northeasterlies. When the radius of the bogus vortex is reduced, the cold front to the north migrates southward in a faster pace than in the control simulation, and rain rate at the front also increases such that total accumulated rainfall at northern Taiwan is comparable with that in the control simulation but with shifted maximum position. In the extreme case in which no bogus vortex is implanted at all, rainfall is mainly associated with evolution of the cold front (pure frontal mode). In addition, a technique is developed to modify the monsoon strength over China. It is found that low-level (1000–700 hPa) reduction in monsoon strength weakens interaction with the typhoon, and rain distribution remains the same as in the control simulation. However, the simulated typhoon track is considerably sensitive to the deep-layer (1000–300 hPa) monsoon strength.

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