A Study of Two Propagating Heavy-Rainfall Episodes near Taiwan during SoWMEX/TiMREX IOP-8 in June 2008. Part II: Sensitivity Tests on the Roles of Synoptic Conditions and Topographic Effects

Abstract

This study is the second of a two-part series to investigate two rainfall episodes in the Hovmöller space near Taiwan during the eighth intensive observing period (IOP-8, 12-17 June 2008) of the Southwest Monsoon Experiment/Terrain-influenced Monsoon Rainfall Experiment (SoWMEX/TiMREX). The first episode moved eastward and the second westward, and both caused heavy rainfall in Taiwan. The goal of Part I was to better understand the mechanism and controlling factors for the organization and propagation of the episodes. Here in Part II, the detailed roles played by synoptic conditions and terrain effects are further examined. Three sensitivity tests (at 2.5-km grid spacing) are designed to include only the effects of synoptic evolution (SNP), and those from land-sea distribution-diurnal variations on top of a mean background with/ without topography (DIU/DNT). As the benchmark, the control (CTL) experiment captures the 6-day event successfully and is validated in Part I.In SNP, the two episodes are reproduced with overall similarity to CTL and the observation, and this confirms that the general location/time of rainfall are mainly controlled by synoptic forcing in this case, in contrast to typical warm-season conditions in the central United States. Even so, diurnal effects can still exert discernible impacts and modulate local convective development in many instances, particularly an afternoon enhancement over terrain, and the averaged diurnal cycle in CTL over southeastern China resembles those in DIU/DNT rather than that in SNP (with no land). The steep topography of Taiwan is especially important for its rainfall distribution, including the heavy rainfall on 16 June through processes as postulated by Xu et al.

The Kinematic and Microphysical Characteristics and Associated Precipitation Efficiency of Subtropical Convection during SoWMEX/TiMREX

“…The low-level warm, moist, and unstable air was found over the north SCS on 16 June (Xu et al 2012;FIG. Wang et al 2014a). The mixing ratio of water vapor (g kg 21 ), wind fields (m s 21 ), and geopotential height (m) at 800, 700, and 500 hPa from the National Centers for Environmental Prediction's (NCEP) Final (FNL) operational global analysis data at 0000 UTC 14-17 Jun are shown as shaded colors, vectors, and contours, respectively.…”

Partitioning of Large-Scale and Local-Scale Precipitation Events by Means of Spatio-Temporal Precipitation Regimes on Corsica

“…It was pointed out by [2] that the topography also leads to small-scale breeze systems which modify the large-scale precipitation signals in the Mediterranean. Depending on the geographical settings of mountainous islands in combination with specific prevailing synoptic conditions, a clear influence of orography particularly on the area of formation and on the intensity and sums of precipitation was found [3,4]. It was shown by [5], for instance, for two heavy precipitation events in Taiwan, that the synoptic situation overlapped the diurnal breeze effects, but that the pronounced topography of the island had a large influence on the spatial variation of the distribution of the precipitation totals.…”

Impact of Synoptic‐Scale Factors on Rainfall Forecast in Different Stages of a Persistent Heavy Rainfall Event in South China

“…Warm‐season heavy rainfall in south China can sometimes sustain for tens of hours (e.g., Davis & Lee, ; Li et al, ; Luo et al, ; Zhang et al, ). Distinct rainfall characteristics and dynamical mechanisms of precipitation have been noticed in different rainfall stages of persistent rainfall events (e.g., Gao et al, ; Wang et al, , 2014b). Notably, in some cases in south China, the forecast skill of precipitation varies from stage to stage during persistent rainfall process (e.g., Gao et al, ).…”