WRF‐based dynamical downscaling of ERA5 reanalysis data for High Mountain Asia: Towards a new version of the High Asia Refined analysis

Abstract

The High Asia Refined analysis (HAR) is a regional atmospheric data set generated by dynamical downscaling of the Final operational global analysis (FNL) using the Weather Research and Forecasting (WRF) model. It has been successfully and widely utilized. A new version (HAR v2) with longer temporal coverage and extended domains is currently under development. ERA5 reanalysis data is used as forcing data. This study aims to find the optimal setup for the production of the HAR v2 to provide similar or even better accuracy as the HAR. First, we conducted a sensitivity study, in which different cumulus, microphysics, planetary boundary layer, and land surface model schemes were compared and validated against in situ observations. The technique for order preference by similarity to the ideal solution (TOPSIS) method was applied to identify the best schemes. Snow depth in ERA5 is overestimated in High Mountain Asia (HMA) and causes a cold bias in the WRF output. Therefore, we used Japanese 55-year Reanalysis (JRA-55) to correct snow depth initialized from ERA5 based on the linear scaling approach. After applying the best schemes identified by the TOPSIS method and correcting the initial snow depth, the model performance improves. Finally, we applied the improved setup for the HAR v2 and computed a oneyear run for 2011. Compared to the HAR, the HAR v2 has a better representation of air temperature at 2 m. It produces slightly higher precipitation amounts, but the spatial distribution of seasonal mean precipitation is closer to observations.

Tropical cyclone simulations over Bangladesh at convection permitting 4.4 km & 1.5 km resolution

“…For all events, RAL2 maximum sustained wind speeds are faster than ERA5 wind speeds (Fig. 4), with median (across all events) ΔERA5 = 35 kn (18 m s −1 ), with the 5 th to 95 th percentiles of the data spanning [10,70] kn ( [5,36] m s −1 ). Comparing IBTrACS, median ΔUS = −6 kn (−3 m s −1 ) and ΔND = 10 kn, (5 m s −1 ).…”

“…Downscaling of ERA5 is reported in a few other studies: Bonanno et al 3 downscale ERA5 using the Weather Research and Forecasting (WRF) model to produce a new 7 km reanalysis over Italy; preliminary work by Taddei et al 4 use ERA5 to force the BOlogna Limited Area Model-MOdello LOCale (BOLAM-MOLOCH) regional model for the purposes of coastal risk assessment in the North Western Mediterranean sea, and Wang et al 5 use ERA5 to run a 10 km WRF domain over high mountain Asia. Specifically examining tropical cyclones, many studies use variations of the Weather Research and Forecasting (WRF) Model 6 , such as Kaur et al 7 who use WRF to downscale the National Center for Environment Prediction (NCEP) Climate Forecast System (CFSv2) and its atmospheric component Global Forecast System (GFS) to 9 km over the north Indian Ocean for two historical cases (Mora and Ockhi), with analysis focusing on the spatial accuracy of rainfall and 850 hPa vorticity, and the vertical profiles of wind and temperature.…”

“…4 use ERA5 to force the BOlogna Limited Area Model-MOdello LOCale (BOLAM-MOLOCH) regional model for the purposes of coastal risk assessment in the North Western Mediterranean sea, and Wang et al . 5 use ERA5 to run a 10 km WRF domain over high mountain Asia. Specifically examining tropical cyclones, many studies use variations of the Weather Research and Forecasting (WRF) Model 6 , such as Kaur et al .…”

Atmospheric triggering conditions and climatic disposition of landslides in Kyrgyzstan and Tajikistan at the beginning of the 21st century

“…Compared to the old version of the High Asia Refined Analysis (HAR) (Maussion et al, 2014), HAR v2 can simulate precipitation over High Mountain Asia as accurately as the old version. Simulation of air temperature at 2 m is better than the old version due to the snow depth correction approach (Wang et al, 2021). Hamm et al (2020) compared the HAR v2 with other gridded precipitation data sets, including reanalysis data and satellite-based precipitation retrieval.…”

Comment on nhess-2020-418

“…It is the only gridded atmospheric data set over High Mountain Asia with high resolution and accuracy (Hamm et al, 2020). Detailed modeling strategies of the HAR v2 are described in Wang et al (2021). The HAR v2 has a grid spacing of 10 km and is available in hourly, daily, monthly and yearly aggregations.…”