The impact of planetary boundary layer parameterisation scheme over the
Yangtze River Delta region, China: Part I - Seasonal and diurnal
sensitivity studies
Abstract
The planetary boundary layer (PBL) is the main region for the exchange
of matter, momentum and energy between land and atmosphere. The
transport processes in the PBL determine the distribution of
temperature, water vapour, wind speed and other physical quantities
within the PBL and are very important for the simulation of the physical
characteristics of the meteorology. Based on the two non-local closure
PBL schemes (YSU, ACM2) and two local closure PBL schemes (MYJ, MYNN) in
the Weather Research and Forecasting (WRF) model, seasonal and daily
cycles of meteorological variables over the Yangtze River Delta (YRD)
region are investigated. It is shown that all the four PBL schemes
overestimate 10-m wind speed and 2-m temperature, while underestimate
relative humidity. The MYJ scheme produces the largest biases on 10-m
wind speed and the smallest biases on humidity, while the ACM2 scheme
show WRF-simulated 2-m temperature and 10-m wind speed are closer to
surface meteorological observations in summer. The ACM2 scheme performs
well with daytime PBL height, the MYNN scheme performs the lowest mean
bias of 0.04 km and the ACM2 scheme shows the highest correlation
coefficient of 0.59 compared with observational data. It is found that
there is a varying degree of sensitivity of the respective PBL in winter
and summer and a best-performing PBL scheme should be chosen to predict
various meteorological conditions under different seasons over a
complicated region like the YRD.