Increasing the credibility of regional climate simulations by introducing subgrid‐scale cloud‐radiation interactions

Abstract

The radiation schemes in the Weather Research and Forecasting (WRF) model have previously not accounted for the presence of subgrid-scale cumulus clouds, thereby resulting in unattenuated shortwave radiation, which can lead to overly energetic convection and overpredicted surface precipitation. This deficiency can become problematic when applying WRF as a regional climate model (RCM). Therefore, modifications were made to the WRF model to allow the Kain-Fritsch (KF) convective parameterization to provide subgrid-scale cloud fraction and condensate feedback to the rapid radiative transfer model-global (RRTMG) shortwave and longwave radiation schemes. The effects of these changes are analyzed via 3 year simulations using the standard and modified versions of WRF, comparing the modeled results with the North American Regional Reanalysis (NARR) and Climate Forecast System Reanalysis data, as well as with available data from the Surface Radiation Network and Clouds and Earth's Radiant Energy System. During the summer period, including subgrid cloudiness estimated by KF in the RRTMG reduces the surface shortwave radiation, leading to less buoyant energy, which is reflected in a smaller diabatic convective available potential energy, thereby alleviating the overly energetic convection. Overall, these changes have reduced the overprediction of monthly, regionally averaged precipitation during summer for this RCM application, e.g., by as much as 49 mm for the southeastern U.S., to within 0.7% of the NARR value of 221 mm. These code modifications have been incorporated as an option available in the latest version of WRF (v3.6).

An RCM multi-physics ensemble over Europe: multi-variable evaluation to avoid error compensation

“…On the other hand, simulations with correct temperatures, as MPE-F, or even too warm, as MPE-D, produce excessive precipitation. It is known that the Kain-Fritsch cumulus scheme overestimates convective precipitation because it does not represent the radiative effect of unresolved cumulus clouds (Herwehe et al 2014;Alapaty et al 2012). Other convection schemes, such as BMJ and GD, could be affected by similar problems, and these would be an important contribution to precipitation overestimation in summer.…”

More homogeneous wind conditions under strong climate change decrease the potential for inter-state balancing of electricity in Europe

“…Assessing changes in solar power generation is arguably more difficult due to, among other things, unresolved processes in relatively coarse climate models and uncertain parameterizations (e.g., Chiacchio et al, 2015;Herwehe et al, 2014). Acknowledging this difficulty and associated uncertainties, an evaluation of the EURO-CORDEX data finds limited impacts of climate change on solar photovoltaic (PV) potentials .…”

Improving High-Resolution Weather Forecasts Using the Weather Research and Forecasting (WRF) Model with an Updated Kain–Fritsch Scheme

“…However, according to Clark et al (2012), many such studies are not able to 88 accurately clarify unique precipitation particle and other physical parameters in different 89 microphysical processes using regional models such as the Weather Research and Forecasting 90 (WRF) model (Skamarock and Klemp 2008). Alapaty et al (2012) and Herwehe et al (2014) 119 emphasized and documented the importance of incorporating such subgrid-scale cloud-radiation 120 interactions using the Kain-Fritsch (KF) convective parameterization scheme (Kain 2004) and 121 the Rapid Radiation Transfer Model, Global (RRTMG) schemes (Iacono et al 2008). In many NWP models, the fractional cloudiness 116 can influence atmospheric radiation budgets as well as the dynamics and thermodynamics, but in 117 the past, subgrid-scale cumulus cloudiness and the associated radiative impacts have been largely 118 neglected outside of global climate models.…”