The Diurnal Cycle of Winds, Rain, and Clouds over Taiwan during the Mei-Yu, Summer, and Autumn Rainfall Regimes

Knowledge about spatial and temporal variations in surface global solar radiation (GSR) and evaporative water loss from the ground are important issues to many researches and applications. In this study empirical relationships suitable for Taiwan were established for GSR retrieval from geostationary satellite images using the Heliosat method for the period from 2011 -2013. The derived GSR data has been used to generate consecutive maps of 10-day averaged pan evaporation (Epan) as the basis to produce regional ET estimation using a strategy that does not require remote sensed land surface temperatures (LST). The retrieved daily GSR and the derived 10-day averaged Epan were validated against pyranometer and class-A pan measurements at selected Central Weather Bureau (CWB) stations spread across various climatic regions in Taiwan. Compared with the CWB observed data the overall relative mean bias deviations (MBD%) and root mean square differences (RMSD%) in daily solar irradiance retrieval were about 5 and 15%, respectively. Seasonally, the largest MBD% and RMSD% of retrieved daily solar irradiance occur in spring (9.5 and 21.3% on average), while the least MBD% (-0.3% on average) and RMSD% (9.7% on average) occur in autumn and winter, respectively. For 10-day averaged Epan estimation, the mean MBD% and RMSD% for stations located in the coastal plain areas were 0.1 and 16.9%, respectively. However, in mountainous areas the mean MBD% and RMSD% increased to 30.2 and 34.5%, respectively. This overestimation was due mainly to the large differences in surrounding micro-environments between the mountainous and plain areas.

Section: Cloud Index Statisticssupporting

confidence: 92%

Solar Irradiance and Pan Evaporation Estimation from Meteorological Satellite Data

Syu¹,

Lee²,

Leou³

et al. 2016

“…Among these weather systems, convective afternoon rainfall (hereafter, CAR) is the most frequently observed pattern (Wang and Chen 2008). Because of its importance to local residents, the characteristics and causes of CAR have been examined in many studies (Chen et al 1991;Johnson and Bresch 1991;Kerns et al 2010;Lin et al 2011;Huang and Chan 2012;Wang et al 2013). Studies have noted that CAR generally occurs on a day associated with a stronger sea breeze circulation during the daytime (e.g., Lin et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Summer Convective Afternoon Rainfall Simulation and Projection Using WRF Driven by Global Climate Model. Part I: Over Taiwan

Huang¹,

Chang

Cheng

et al. 2016

This paper is the first of a two-part study that investigates summer convective afternoon rainfall (CAR) activity over the East Asian continent through simulation and projection. We focus on the CAR activity over Taiwan in Part I. In Part II, the changes in CAR activity over South China and Luzon are examined. Using the WRF (Weather Research and Forecasting) model driven by two super-high resolution global climate models: HiRAM (High Resolution Atmospheric Model) and MRI (Meteorological Research Institute Atmospheric General Circulation Model), this study evaluates the performance of models (HiRAM, MRI, and WRF) used to simulate the summer CAR activity over Taiwan. The evaluations focus on the spatialtemporal variations in CAR activity during two time periods: the present-day (1979 -2003, historical run) and the future (2075 -2099, RCP8.5 scenario). For the present-day simulations, analyses indicate that both HiRAM and MRI cannot accurately simulate the temporal evolution of diurnal rainfall. This timing shift problem can be fixed after dynamical downscaling using WRF. The WRF dynamical downscaling approach also helps generate a more realistic CAR amount simulation over western Taiwan, where most residents live. In future projections all models predict that a significant decrease in CAR amount will occur over southwest Taiwan. This decrease in CAR amount is suggested due to the decrease in CAR frequency, not a change in the CAR rate. All models suggest that the cause of decrease in CAR frequency over southwest Taiwan is weaker local afternoon surface wind convergence and thermal instability to suppress CAR genesis.

“…Nevertheless, for all three cases studied, localized heavy rainfall occurs at night as the surface front approaches with increasing strength of the pre-frontal southwesterly monsoon flow. Previous studies have shown that orographic blocking is most pronounced at night and in the early morning when the land surface is coldest (Chen and Li 1995b;Kerns et al 2010;Lin et al 2011).…”

Section: Orographic Effects As the Low-level Trough Approaches Taiwanmentioning

confidence: 99%

“…It is well known that the interaction between the cold pool of convective cells and the environmental flow can enhance convection (Kerns et al 2010;Markowsla and Richardson 2010). At 20 LST 2 June, when the simulated precipitation system is still over the southeastern coast of China (Fig.…”

Section: The Cold Pool From Convectionmentioning

confidence: 99%

“…Convective activity could develop or strengthen over the northwest/west coast of Taiwan (Kerns et al 2010) if offshore convergence is coupled with upper-level divergence under favorable largescale conditions (Chen and Li 1995a;Li et al 1997). Furthermore, the strength of the barrier jet is strongest in the early morning when the land surface is coldest (Chen and Li 1995b;Lin et al 2011).…”

Section: Introductionmentioning

confidence: 99%

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Revisiting the Heavy Rainfall Event over Northern Taiwan on 3 June 1984

Chen¹,

Chen²,

Chen³

et al. 2013

Self Cite

In this study, the mechanisms for the development of a localized heavy rainfall event during the evening of 2 June to the early morning of 3 June 1984 over northern Taiwan are investigated. This event occurred under favorable large-scale conditions including: upper-level divergence; low-level high equivalent potential temperature; low levels of free convection; and subsynoptic-scale ascending motion over the northern Taiwan Strait and northern Taiwan associated with a baroclinic front. In the late night of 2 June, pre-existing rainfall is simulated to the southeast of a trough axis over the southeastern China coast as well as in the frontal zone north of Taiwan. The pre-existing rainfall is enhanced as it moves over the northeastern Taiwan Strait where the prevailing southwesterly winds within the Taiwan Strait converge with the orographically deflected flow with a southerly wind component off the western/northwestern Taiwan coast. As the pre-existing convective rainfall continues to move toward northern Taiwan, it is further enhanced in a localized low-level convergence zone over the northwestern coast where a barrier jet along the coast converges with the northwesterly winds behind the surface front. Furthermore, on the morning of 3 June, focusing of rainfall is simulated where the barrier jet encounters the leading edge of the cold pool caused by rain evaporative cooling. As the convective rainfall areas drift inland, the orographic lifting of the pre-frontal southwesterly flow over the slopes south of the Taipei Basin also plays a role in the simulated enhanced heavy rainfall there.