The Role of Mesoscale and Topographically Induced Circulations in Initiating a Flash Flood Observed during the TAMEX Project

Akaeda, Kenji; Reisner, Jon; Parsons, David B.

doi:10.1175/1520-0493(1995)123<1720:tromat>2.0.co;2

Cited by 52 publications

(29 citation statements)

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“…1). Mountains not only generate local circulations but also interact with large-scale low-level winds to produce localized rain showers (Akaeda et al 1995;Li et al 1997). The sealand breeze and anabatic-katabatic flows are important in moistening the boundary layer to provide favorable conditions for the initiation of afternoon thunderstorms (Johnson and Bresch 1991;Chen and Li 1995).…”

Section: Introductionmentioning

confidence: 99%

Warm Season Afternoon Thunderstorm Characteristics under Weak Synoptic-Scale Forcing over Taiwan Island

Lin

Chang²,

Jou

et al. 2011

Weather and Forecasting

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The spatial and temporal characteristics and distributions of thunderstorms in Taiwan during the warm season (May-October) from 2005 to 2008 and under weak synoptic-scale forcing are documented using radar reflectivity, lightning, radiosonde, and surface data. Average hourly rainfall amounts peaked in midafternoon (1500-1600 local solar time, LST). The maximum frequency of rain was located in a narrow strip, parallel to the orientation of the mountains, along the lower slopes of the mountains. Significant diurnal variations were found in surface wind, temperature, and dewpoint temperature between days with and without afternoon thunderstorms (TS A and non-TS A days). Before thunderstorms occurred, on TS A days, the surface temperature was warmer (about 0.58-1.58C) and the surface dewpoint temperature was moister (about 0.58-28C) than on non-TS A days. Sounding observations from northern Taiwan also showed warmer and higher moisture conditions on TS A days relative to non-TS A days. The largest average difference was in the 750-550-hPa layer where the non-TS A days averaged 2.58-3.58C drier. These preconvective factors associated with the occurrences of afternoon thunderstorms could be integrated into nowcasting tools to enhance warning systems and decision-making capabilities in real-time operations.

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Section: Introductionmentioning

confidence: 99%

Warm Season Afternoon Thunderstorm Characteristics under Weak Synoptic-Scale Forcing over Taiwan Island

Lin

Chang²,

Jou

et al. 2011

Weather and Forecasting

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“…Besides the role of the terrain on flow dynamics, the island of Taiwan can also exhibit strong thermodynamic effects in early summer, through daytime solar heating (and nighttime cooling) and the development of diurnal circulation (such as land-sea and mountain valley breezes) over complex terrain (e.g., Akaeda et al 1995;Chen et al 1999). While these effects also modify the stability of the flow (e.g., Georgelin et al 1996), they provide local forcing for convective development and are responsible for the pronounced diurnal variation in both total rainfall and the heavy-rainfall frequency over Taiwan in the mei-yu season (e.g., Yeh and Chen 1998;Chen et al 1999).…”

Section: Introductionmentioning

confidence: 99%

Remote Trigger of Deep Convection by Cold Outflow over the Taiwan Strait in the Mei-Yu Season: A Modeling Study of the 8 June 2007 Case

2011

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In this study, the heavy-rainfall event over central Taiwan during the mei-yu season on 8 June 2007 is investigated, with an emphasis on the triggering mechanism for the deep convection that produced the rain. Observations indicate that there existed two lines of forcing with convection prior to the rain: one over the northern Taiwan Strait along the mei-yu front and the other over the southern Taiwan Strait. Yet, the convection in question developed over the central strait between these two lines, in an unstable environment with strong westerly vertical wind shear. This motivated the authors to carry out the present study.The Cloud-Resolving Storm Simulation (CReSS) of Nagoya University was used and the event was reproduced at a horizontal grid size of 2 km, including the initiation of new convection over the central strait at the correct location and time. The model results suggest a crucial role played by the series of active, persistent, and propagating storms in the southern strait (along the aforementioned second forcing line). On their back (northern) side, these storms repeatedly produced pulses of cold outflow that traveled toward the north-northeast with positive pressure perturbation. With characteristics of gravity waves, the perturbation propagated faster than the cold air and the associated increase in forward-directed (horizontal) pressure gradient force led to northward acceleration of near-surface flow (by up to 4-5 m s 21 h 21 ). The stronger southerly flow in turn enhanced downstream convergence, and the deep convection was triggered in the central strait near the arrival of the gravity wave ahead of the cold air. When the convection moved eastward over Taiwan, heavy rainfall resulted. The mechanism presented here for remote triggering of convection over the ocean has not been documented near Taiwan during the mei-yu season. With a better understanding about the behavior of convection, these results can contribute to the improvement of quantitative precipitation forecasts and hazard prevention and reduction.

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“…Orographic effects on rainfall over the western, windward slopes of the CMR during the 1987 Mei-yu season, part of the southwesterly monsoon regime, have been studied extensively (Yeh and Chen 1998). summarized the orographic effects on the 1987 Mei-yu into lifting (Yeh and Chen 1998;Trier et al 1990), blocking (Li et al 1997;Akaeda et al 1995), and thermal effects ( Chen et al 1991;Johnson and Bresch 1991;Akaeda et al 1995;Yeh and Chen 1998;Lin and Chen 2002). Recently, Bresch (2001) investigated a morning cloud band with light rain showers parallel to the Taiwan east coast.…”

Section: Introductionmentioning

confidence: 99%

Characteristics of Heavy Summer Rainfall in Southwestern Taiwan in Relation to Orographic Effects

Chen

Tao

2004

Journal of the Meteorological Society of Japan

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About a quarter to a half of all rainfall from mid-July through August from 1994 to 2000, on the windward side of southwestern Taiwan, came from convective systems embedded in the monsoon flow associated with the southwesterly monsoon. In this study, the causes of two heavy rainfall events (daily rainfall exceeding 100 mm day À1 over at least three rainfall stations), observed over the slopes and/or lowlands of southwestern Taiwan were examined. Data from the European Center for Medium-Range Weather Forecasts/Tropical Ocean-Global Atmosphere (EC/TOGA) analyses, the rainfall stations of the Automatic Rainfall and Meteorological Telemetry System (ARMTS) and the conventional surface stations over Taiwan, and the simulation results from a regional-scale numerical model were used to accomplish the objectives. In one event, on 9 August 1999, heavy rainfall of up to 393 mm was observed over the windward slopes of southern Taiwan in a potentially unstable environment, with very humid air around 850 hPa. The extreme accumulation was simulated and attributed to orographic lifting effects as preexisting convection did not drift into western Taiwan from the Taiwan Strait.In another event, on 13 August 1994, with a maximum rainfall of 450 mm, westerly flow with potentially unstable and very moist air in the lowest layers, converged with northwesterly flow from the central Taiwan Strait over the southwestern coast. The westerly flow decelerated while approaching Taiwan, resulting in enhanced convergence and upward motion over the coastal area and a high amount of rainfall. In addition, a mesoscale convergence area was produced over the southern Taiwan Strait near the southwestern coast of Taiwan due to synoptic circulations. Some convection formed in the ocean near the southwest coast and drifted inland. This situation also enhanced precipitation over the coastal areas. Northwesterly flow formed over the southwestern slopes as weak westerly flow approached the mountains. As rainwater from the Strait and coastal areas moved eastward toward the slopes, the northwesterly flow transported the rainwater southeastward away from the southwestern slopes. Subsequently, less rainfall occurred over the southwestern slopes than over the coastal areas.

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The Role of Mesoscale and Topographically Induced Circulations in Initiating a Flash Flood Observed during the TAMEX Project

Cited by 52 publications

References 0 publications

Warm Season Afternoon Thunderstorm Characteristics under Weak Synoptic-Scale Forcing over Taiwan Island

Warm Season Afternoon Thunderstorm Characteristics under Weak Synoptic-Scale Forcing over Taiwan Island

Remote Trigger of Deep Convection by Cold Outflow over the Taiwan Strait in the Mei-Yu Season: A Modeling Study of the 8 June 2007 Case

Characteristics of Heavy Summer Rainfall in Southwestern Taiwan in Relation to Orographic Effects

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