Sensitivity of Simulations of Zambian Heavy Rainfall Events to the Atmospheric Boundary Layer Schemes

Climate

Edward Rakate¹  Robert S. Plant²  Mary-Jane M. Bopape³  Elelwani Phaduli³  Robert Maisha³  Edson Nkonde⁴  David Waitolo⁴  Stein Mkandawire⁵  Henry Simfukwe⁵ 

[1] Centre for High Performance Computing, Council for Scientific and Industrial Research, P.O. Box 395, Pretoria 0001, South Africa;Department of Meteorology, University of Reading, Reading RG6 6ET, UK;South African Weather Service, Private Bag X097, Pretoria 0001, South Africa;Zambia Meteorological Department, P.O. Box 50065, Lusaka, Zambia;Zambia Research and Education Network, School of Education Building First Floor, University of Zambia, West Wing P.O. Box 32379, Lusaka, Zambia;

关键词: flooding;    weather forecasting;    high performance computing;    boundary layer scheme;   

DOI  :  10.3390/cli9020038

来源: DOAJ

【 摘 要 】

Weather forecasting relies on the use of numerical weather prediction (NWP) models, whose resolution is informed by the available computational resources. The models resolve large scale processes, while subgrid processes are parametrized. One of the processes that is parametrized is turbulence which is represented in planetary boundary layer (PBL) schemes. In this study, we evaluate the sensitivity of heavy rainfall events over Zambia to four different PBL schemes in the Weather Research and Forecasting (WRF) model using a parent domain with a 9 km grid length and a 3 km grid spacing child domain. The four PBL schemes are the Yonsei University (YSU), nonlocal first-order medium-range forecasting (MRF), University of Washington (UW) and Mellor–Yamada–Nakanishi–Niino (MYNN) schemes. Simulations were done for three case studies of extreme rainfall on 17 December 2016, 21 January 2017 and 17 April 2019. The use of YSU produced the highest rainfall peaks across all three cases; however, it produced performance statistics similar to UW that are higher than those of the two other schemes. These statistics are not maintained when adjusted for random hits, indicating that the extra events are mainly random rather than being skillfully placed. UW simulated the lowest PBL height, while MRF produced the highest PBL height, but this was not matched by the temperature simulation. The YSU and MYNN PBL heights were intermediate at the time of the peak; however, MYNN is associated with a slower decay and higher PBL heights at night. WRF underestimated the maximum temperature during all cases and for all PBL schemes, with a larger bias in the MYNN scheme. We support further use of the YSU scheme, which is the scheme selected for the tropical suite in WRF. The different simulations were in some respects more similar to one another than to the available observations. Satellite rainfall estimates and the ERA5 reanalysis showed different rainfall distributions, which indicates a need for more ground observations to assist with studies like this one.

【 授权许可】

Unknown