A simple height-based correction for temperature downscaling in complex terrain

Abstract

ABSTRACT:A new downscaling method has been developed to improve forecasts of near-surface temperature. This involves applying a correction to forecast temperatures to account for the difference in height between the terrain in the forecast model and the real terrain, using an estimate of the lapse rate of temperature. The strongest variations in lapse rate are found to occur overnight, being a function of cloud cover and geostrophic wind speed. These variables similarly influence the night time lapse rate in the UK Met Office Unified Model forecast at 4 km resolution. Therefore, a simple algorithm has been employed to estimate the lapse rate at a given location, based on forecast model temperature and elevation fields. The algorithm has a positive impact on performance in stable conditions, compared to assuming an adiabatic lapse rate at all times.  Crown

Performance of the WRF model to simulate the seasonal and interannual variability of hydrometeorological variables in East Africa: a case study for the Tana River basin in Kenya

“…This is in agreement with Sheridan et al (2010). The results shown as time series can also be confirmed in the seasonal average maps (Online resources 1 & 2).…”

Cold‐pool formation in a narrow valley

“…The results from this study potentially have important implications for the development of post-processing techniques designed to account for the effect of subgrid terrain on NWP and climate-model temperature predictions (Sheridan et al, 2010). The importance of the sheltering effect suggests that a parametrization to account for reduced downward turbulent heat flux in subgrid valleys could be used to improve temperature predictions in complex terrain.…”

“…The details of high-impact weather such as fog, ice and air pollution remain unresolved by current numerical weather prediction (NWP) models. Post-processing techniques (Sheridan et al, 2010) can be used to add local subgrid detail to NWP forecasts, but these require an understanding of the key small-scale phenomena in order to improve the forecasts consistently. The boundary-layer parametrizations used in NWP and climate models are also known to be deficient under strongly stable conditions (Cuxart et al, 2006).…”

COLPEX: Field and Numerical Studies over a Region of Small Hills

“…Figure 11 is indicative of the degree of subgrid-scale variability that is likely to go unrepresented in a forecast over terrain of this kind. Previous work by Sheridan et al (2010) showed that a simple extrapolation technique based on altitude together with an estimate of lapse rate could be used to predict subgrid variations. Their scheme, however, does not account for valley flow processes such as sheltering by surrounding terrain, which are expected to be active in generating the cold extremes seen in these small valleys.…”

“…In addition to these local effects on temperature and fog formation, the mixing and transport processes occurring in complex terrain can impact the larger-scale flow and so there is a need to correctly parameterize these processes in coarse-resolution weather forecasting and climate models. Such errors may be responsible for observed cold biases over complex terrain in some models (Sheridan et al 2010). The large observed temperature variations in cold pools mean that  In the low (up to 10 0 m) hills and narrow (1-3 km wide) valleys of Shropshire, atmospheric conditions-including cold-air pooling and fog-can range widely over such short distances that they escape the attention of numerical forecast models.…”