WRF Model Sensitivity to Choice of Parameterization over South America: Validation against Surface Variables

Abstract

The Weather and Research Forecast model is tested over South America in different configurations to identify the one that gives the best estimates of observed surface variables. Systematic, nonsystematic, and total errors are computed for 48-h forecasts initialized with the NCEP Global Data Assimilation System (GDAS). There is no unique model design that best fits all variables over the whole domain, and nonsystematic errors for all configurations differ little from one another; such differences are in most cases smaller than the observed day-to-day variability. An ensemble mean consisting of runs with different parameterizations gives the best skill for the whole domain. Surface variables are highly sensitive to the choice of land surface models. Surface temperature is well represented by the Noah land model, but dewpoint temperature is best estimated by the simplest land surface model considered here, which specifies soil moisture based on climatology. This underlines the need for better understanding of humid processes at the subgrid scale. Surface wind errors decrease the intensity of the low-level jet, reducing expected heat and moisture advection over southeast South America (SESA), with negative precipitation errors over SESA and positive biases over the South Atlantic convergence zone (SACZ). This pattern of errors suggests feedbacks between wind errors, precipitation, and surface processes as follows: an increase of precipitation over the SACZ produces compensating descent in SESA, with more stable stratification, less rain, less soil moisture, and decreased rain. This is a clear example of how local errors are related to regional circulation, and suggests that improvement of model performance requires not only better parameterizations at the subgrid scales, but also improved regional models.

Evaluation of TRMM 3B42 precipitation estimates and WRF retrospective precipitation simulation over the Pacific–Andean region of Ecuador and Peru

“…In general, correlation increases with time scale, and is higher for monthly than 15-day and weekly time aggregated periods. Bias seems to accumulate when time aggregation increases, as found for WRF in other regions (Cheng and Steenburgh, 2005;Ruiz et al, 2010). The purpose of finding the relative bias in the estimates is to quantify respectively the over-/underestimation of the precipitation depth.…”

Impacts of a Groundwater Scheme on Hydroclimatological Conditions over Southern South America

“…WRF exhibits biases in different variables over South America (e.g., Ruiz et al 2010;Lee 2010), likely due to problems with different components of the model, as is the general case for different regional climate models (RCMs) over the region (e.g., Solman et al 2013). For example, previous studies report good skill of some parameterizations in some regions of South America, but a poor performance in other regions of the continent [see Solman and Pessacg (2012) for a comprehensive sensitivity study with MM5].…”

Relative impacts of land use and climate change on summer precipitation in the Netherlands

“…The sensitivity to different parameterization schemes was not specifically investigated in this study, while this is known to be important (Gallus and Bresch, 2006;Jankov et al, 2005;Rajeevan et al, 2010;Ruiz et al, 2010;Zeng et al, 2012;ter Maat et al, 2013). The chosen YSU PBL scheme is a first-order nonlocal scheme that is widely used under convective conditions (Hu et al, 2010).…”