Numerical Modeling of an Orographically Enhanced Precipitation Event Associated with Tropical Storm Rachel over Taiwan

Chiao, Sen; Lin, Yuh-Lang

doi:10.1175/1520-0434(2003)018<0325:nmoaoe>2.0.co;2

Cited by 41 publications

(37 citation statements)

References 32 publications

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“…The occurrence of consistent model rainfall predictions is, of course, not mere coincidence, but rather a consequence of the "terrain-locking" mechanism as mentioned in the introduction. Predictability of the accumulated rainfall associated with typhoons impinging Taiwan at different directions was also shown by Lin et al (2002), Wu et al (2002Wu et al ( , 2009), Chiao and Lin (2003), Huang et al (2005) and Yang et al (2008) using MM5, and by Chien et al (2008) and using WRF. These successful rainfall predictions benefited essentially from the presence of the high CMR in Taiwan that provides the orographic uplift of typhoon flow to produce intense rainfall.…”

Section: Rainfall Predictionsupporting

confidence: 86%

“…The interaction between the typhoon vortex and the CMR which cause track deviations and different rainfall activities has long been a challenging problem tackled by numerous studies (e.g., Chang 1982;Bender et al 1987;Yeh and Elsberry 1993a, b;Lin et al 2002Lin et al , 2005Wu et al 2002Wu et al , 2009Chiao and Lin 2003;Huang et al 2005;Jian and Wu 2008;Yang et al 2008Yang et al , 2011Chien and Kuo 2011). The intense flow associated with a typhoon striking Taiwan tends to produce persistent heavy rains over the steep windward slopes, a situation favorable for a possible "terrain-locking" mechanism that somewhat reduces the difficulty in obtaining rainfall predictability (Wu et al 2002Lin et al 2005).…”

Section: Introductionmentioning

confidence: 84%

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Extreme Rainfall Mechanisms Exhibited by Typhoon Morakot (2009)

Huang¹,

Wong²,

Yeh³

2011

Terr. Atmos. Ocean. Sci.

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Moderate Typhoon Morakot (2009) became the most catastrophic typhoon in Taiwan on record. The MM5 numerical experiments with and without bogus data assimilation (BDA) were used to investigate the extreme rainfall mechanisms in Taiwan associated with the westbound typhoon. The BDA, based on 4DVAR, helps MM5 to maintain a more consolidated typhoon vortex and better predict the observed track after landfall, thus producing realistic extreme rainfall (about 2400 mm) at the southern and Central Mountain Range (CMR) of Taiwan. Severe rainfall in Taiwan is dominated by the CMR that hence modulates rainfall predictability.Model analyses indicate that the synoptic environment provides low-level preconditioning with large convective available energy (CAPE) in the southwest monsoon conveying belt in conjunction with the cyclonic Morakot. When Morakot passed slowly over north Taiwan, the developing Tropical Storm Goni, originating west of Hong Kong, facilitated the moist southwesterly flow to converge with the northerly cyclonic flow of Morakot. These processes contributed to enhanced rainfall in south Taiwan. In an experiment whereby the Goni vortex was initially deactivated by BDA, the southwesterly prevailing flow, southwest of Taiwan, weakened considerably and shifted southward at a later time, resulting in one-third reduction in total accumulated rainfall in south Taiwan. Conversely, total accumulated rainfall in Taiwan is greatly reduced when the initial Morakot vortex is deactivated. Removal of Taiwan topography results in a significant reduction in total accumulated rainfall by more than 50%, due to lack of orographic lift by the CMR.

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Section: Rainfall Predictionsupporting

confidence: 86%

Section: Introductionmentioning

confidence: 84%

Extreme Rainfall Mechanisms Exhibited by Typhoon Morakot (2009)

Huang¹,

Wong²,

Yeh³

2011

Terr. Atmos. Ocean. Sci.

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“…Previous modeling results (Chiao and Lin 2003;Yang et al 2008;Fang et al 2011;and others) have also suggested that the terrain could enhance precipitation from tropical cyclones. Additional tests reducing the Taiwan terrain height by 25, 50, and 75% reduced the amount of heavy rainfall by 16, 27 and 39%, respectively.…”

Section: Comparison With Observationsmentioning

confidence: 99%

High-Resolution Numerical Simulation of the Extreme Rainfall Associated with Typhoon Morakot. Part I: Comparing the Impact of Microphysics and PBL Parameterizations with Observations

Wei¹,

Shi²,

Lin³

et al. 2011

Terr. Atmos. Ocean. Sci.

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Typhoon Morakot hit Taiwan the night of 7 August 2009 as a Category 1 storm and caused up to 3000 mm of rain, leading to the worst flooding there in 50 years as well as devastating mudslides. The Weather Research and Forecasting model (WRF) is used at high resolution to simulate this extreme weather event. The model results indicate that WRF is able to capture the amount and location of the observed surface rainfall and that the typhoon-induced circulation, orographic lifting and a moisture-abundant southwest flow are the main mechanisms that together produced the tremendous rainfall in this case. Furthermore, the model results suggest that the agreement with the observed rainfall is due to the simulated storm track and intensity being in relatively good agreement with the observed. Additional simulations were made to examine the sensitivity of this case to model physics (microphysics and planetary boundary layer or PBL). Both warm rain only as well as improved microphysics yield similar significant rain amounts at the same locations as the control case. The improved microphysics lead to a better storm intensity early on but later exceed the observed intensities by about 10 hPa. The stronger storm arises from less evaporative cooling from cloud and rain and consequently weaker simulated downdrafts. Warm rain results closely match the control (i.e., the track, intensity, and maximum rainfall locations/amounts), implying ice processes (i.e., additional heat release due to ice processes) have only a secondary effect on surface rainfall. Results are less sensitive to using different PBL schemes than different microphysics.

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“…They concluded that orographic forcing, rather than the original rainbands of the typhoon, controlled heavy rainfall in the vicinity of the mountains. Chiao and Lin (2003) used a similar methodology for Tropical Storm Rachel and found evidence that topographic enhancement of preexisting convective bands, along with more local topographically induced flows and deep convection, were important factors in the observed rainfall distribution. Wu et al (2002) investigated the impact of Typhoon Herb (1996), and also found strong topographic forcing was critical to accumulated rainfall during the event, especially at the heavy rainfall end of the distribution.…”

Section: Introductionmentioning

confidence: 99%

High-Resolution Modeling of Typhoon Morakot (2009): Vortex Rossby Waves and Their Role in Extreme Precipitation over Taiwan

Hall

Xue

Ran

et al. 2013

Journal of the Atmospheric Sciences

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A high-resolution nonhydrostatic numerical model, the Advanced Regional Prediction System (ARPS), was used to simulate Typhoon Morakot (2009) as it made landfall over Taiwan, producing record rainfall totals. In particular, the mesoscale structure of the typhoon was investigated, emphasizing its associated deep convection, the development of inner rainbands near the center, and the resultant intense rainfall over western Taiwan.Simulations at 15-and 3-km grid spacing revealed that, following the decay of the initial inner eyewall, a new, much larger eyewall developed as the typhoon made landfall over Taiwan. Relatively large-amplitude wave structures developed in the outer eyewall and are identified as vortex Rossby waves (VRWs), based on the wave characteristics and their similarity to VRWs identified in previous studies.Moderate to strong vertical shear over the typhoon system produced a persistent wavenumber-1 (WN1) asymmetric structure during the landfall period, with upward motion and deep convection in the downshear and downshear-left sides, consistent with earlier studies. This strong asymmetry masks the effects of WN1 VRWs. WN2 and WN3 VRWs apparently are associated with the development of deep convective bands in Morakot's southwestern quadrant. This occurs as the waves move cyclonically into the downshear side of the cyclone. Although the typhoon track and topographic enhancement contribute most to the recordbreaking rainfall totals, the location of the convective bands, and their interaction with the mountainous terrain of Taiwan, also affect the rainfall distribution. Quantitatively, the 3-km ARPS rainfall forecasts are superior to those obtained from coarser-resolution models.

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Numerical Modeling of an Orographically Enhanced Precipitation Event Associated with Tropical Storm Rachel over Taiwan

Cited by 41 publications

References 32 publications

Extreme Rainfall Mechanisms Exhibited by Typhoon Morakot (2009)

Extreme Rainfall Mechanisms Exhibited by Typhoon Morakot (2009)

High-Resolution Numerical Simulation of the Extreme Rainfall Associated with Typhoon Morakot. Part I: Comparing the Impact of Microphysics and PBL Parameterizations with Observations

High-Resolution Modeling of Typhoon Morakot (2009): Vortex Rossby Waves and Their Role in Extreme Precipitation over Taiwan

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