Taiwan and United States are going to conduct a joint field experiment during
the period of May 15 to June 30, 2008 at the western plain and mountain slope
region of southern Taiwan. It is called Southwest Monsoon Experiment/Terrain-influenced
Monsoon Rainfall Experiment (SoWMEX/ TiMREX). The goal of the program is to
improve the capability of quantitative precipitation estimation and forecasting
(QPE/QPF) during the Asian Summer Monsoon season. The localized heavy rainfall
events frequently lead to floods and landslides resulted in casualty and heavy
property damage in the Taiwan area. SoWMEX/TiMREX provides a unique opportunity
to advance our basic understanding of physical processes leading to development
of heavy orographic precipitation through intensive field observation campaign.
SoWMEX/TiMREX provides an unprecedented opportunity for complementing the science
of previous investigations in the general area of orographic precipitation. The
primary observational facilities to be deployed at southern Taiwan include: NCAR
SPOL (S-band polarimetric Doppler radar system), TEAM-Radar (X-band mobile polarimetric
Doppler radar system), and MRR (Micro rain radar systems). In addition to these advanced
radar systems, Taiwan will provide upstream soundings by operating dropsondes and ship
soundings over the northern boundary of South China Sea.
The major expectation and contribution of SoWMEX/TiMREX is to provide better data set for
understanding of the kinematic and thermodynamic characteristics of the southwesterly
prevailing flows over the ocean upstream during Asian summer monsoon. It is anticipated
that rainfall prediction products during the season will be greatly improved with this
extensive observation campaign. The rainfall products will be valuable not only for early
warning of flood and landslide but also for regional water resource management. The primary
funding supports are from National Science Foundation of USA and National Science Council
and Central Weather Bureau of Taiwan.
A pilot experiment has been conducted in May-June 2007. Dropsonde observations in 5
consecutive days were undertaken over the Taiwan Strait for a heavy rain event in central
and southern Taiwan. Deep and wide spread low level moisture-abundant southwesterly were
observed. Organized convective systems formed over the strait and propagated eastward
producing heavy rain over the sloping area of Central Mountain Range. Data assimilation
tests using these dropsonde observations are performed to simulate the evolution of the
organized convections in high resolution mesoscale model. Research work using this data set
for a better initial data description is now under investigation.