Theoretical Assessment of Uncertainty in Regional Averages due to Network Density and Design

Abstract

Weather Research and Forecasting (WRF) model simulations are performed over Russia for July and December 2005, 2006, and 2007 to create a ?dataset? to assess the impact of network density and design on regional averages. Based on the values at all WRF grid points, regional averages for various quantities are calculated for 2.8° ? 2.8° areas as the ?reference.? Regional averages determined based on 40 artificial networks and 411 ?sites? that correspond to the locations of a real network are compared with the reference regional averages. The 40 networks encompass 10 networks of 500, 400, 200, or 100 different randomly taken WRF grid points as sites. The real network?s site distribution misrepresents the landscape. This misrepresentation leads to errors in regional averages that show geographical and temporal trends for most quantities: errors are lower over shores of large lakes than coasts and lowest over flatland followed by low and high mountain ranges; offsets in timing occur during frontal passages when several sites are passed at nearly the same time. Generally, the real network underestimates regional averages of sea level pressure, wind speed, and precipitation over Russia up to 4.8 hPa (4.8 hPa), 0.7 m s?1 (0.5 m s?1), and 0.2 mm day?1 and overestimates regional averages of 2-m temperature, downward shortwave radiation, and soil temperature over Russia up to 1.9 K (1.4 K), 19 W m?2 (14 W m?2), and 1.5 K (1.8 K) in July (December). The low density of the ten 100-site networks causes difficulties for sea level pressure. Regional averages obtained from the 30 networks with 200 or more randomly distributed sites represent the reference regional averages, trends, and variability for all quantities well.