Incorporation of Various Stability Correction Functions for Computation of Surface Fluxes in Weather Research and Forecasting Model: An Evaluation over an Indian Region

The stability correction functions for momentum (ψm) and heat (ψh) are used in the computation of surface fluxes in both numerical weather prediction and general circulation models. Various functional forms for ψm and ψh are available in the literature, based on the different field experiments. The performance of some of the recently developed functions for ψm and ψh has not yet been analysed in Weather Research and Forecasting Model (WRF), in spite of the fact that they may perform better over different locations and seasons. The aim of this study is to incorporate some of the well-established non-linear functions for ψm and ψh (Dyer, 1974 and Holtslag et al., 1990 (D74/H90); Beljaars and Holtslag, 1991 (BH91); Cheng and Brutsaert, 2005 (CB05); Grachev et al., 2007 (GR07); Srivastava et al., 2020 (GR07/SR20) and Gryanik et al., 2020 (GR07/SRY20)) under stable stratification in the revised MM5 surface layer scheme of WRF model version 4.2.2 and to evolve a procedure having a provision for multiple options for ψm and ψh under stable stratification. Moreover, the performance of these incorporated functions in surface layer scheme has been analysed in simulating near-surface atmospheric variables over an Indian region. Simulations have been conducted with three nested domains at a fine spatial resolution centered around the location of micrometeorological tower installed at Ranchi (23.4120N, 85.4400E), India for January 2009 and simulated results have been compared against the observational dataset from the flux tower.

Initial results suggest that the GR07/GRY20 functions produced larger values of |ψm| than all other functions. However, in case of |ψh|, the functional form corresponding to BH91 leads to higher values at higher stabilities. The rate of decrease of transfer coefficients for momentum (CD) and heat (CH) are comparable for near neutral to moderately stable conditions. However, at higher stabilities, the rate of decrease of CH is relatively faster with D74/H90 and relatively slower for GR07/GRY20, followed by GR07/SR20 and GR07 functions. Moreover, GR07/SR20 functions performed relatively better than all other functions and noticeably reduced the bias for nocturnal 2-m temperature and 10-m wind speed. Further, recommendations have been made for the performance of incorporated functions over Indian region.

References:

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Cheng, Y., & Brutsaert, W. (2005). Flux-profile Relationships for Wind Speed and Temperature in the Stable Atmospheric Boundary Layer. Boundary-Layer Meteorology, 114, 519-538.

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Grachev, A. A., Andreas, E. L., Fairall, C. W. (2007). SHEBA flux-profile relationships in the stable atmospheric boundary layer. Boundary-Layer Meteorology, 124, 315-333.

Gryanik, Vladimir M, Christof Lüpkes, Andrey Grachev, and Dmitry Sidorenko. (2020). "New Modified and Extended Stability Functions for the Stable Boundary Layer Based on SHEBA and Parametrizations of Bulk Transfer Coefficients for Climate Models." Journal of the Atmospheric Sciences, 77, 2687-2716.

Holtslag, A. A. M., De Bruin, E. I. F., and Pan, H. (1990). A High-Resolution Air Mass Transformation Model for Short-Range Weather Forecasting. Monthly Weather Review, 118, 1561-1575.

Srivastava, P., Sharan, M., Kumar, M., & Dhuria, A. K. (2020). On stability correction functions over the Indian region under stable conditions. Meteorological Applications, 27:e1880.