An area and distance weighted analysis of the impacts of station

14 15 16 [plus additional co-authors that will be named at the time of submission to the journal] 17 2 Abstract 18 In Fall et al, 2011, results from the recently concluded Surface Stations Project surveying 19 the U.S. Historical Climatology Network (USHCN) were presented, using a siting 20 classification system developed by Michel Leroy for Meteofrance in 1999, and employed 21 system to introduce a "maintained performance classification" which quantifies the effect 24 of heat sinks and sources within the thermometer viewshed by calculation of the area-25 weighted and distance-weighted impact of biasing elements such as concrete, asphalt, 26 runways, tarmac, and buildings, creating a new site classification that more accurately 27 reflects the representivity of the station exposure. The new area and distance weighted 28 classification system does a more complete job of siting assessment, particularly when 29 applied retroactively to existing stations, than the original distance weighted 30 classification system described in Leroy (1999) , which performs well for new station 31 siting evaluation, but does not take into account the surface area of heat sinks and sources 32 that may encroach upon a temperature measurement station over its lifetime. 33 In Fall et al. (2011), using Leroy's 1999 classification system, it was demonstrated that 34 station exposure affects USHCNv2 temperatures, in particular the minimum 35 temperatures, but showed little difference in mean temperature trends used to assess 36 climate variability. Menne et al. (2010), and Muller et al. (2012), both of which also used 37 the older Leroy (1999) classification system, suggested there is little if any mean 38 3 temperature trend difference between well and poorly sited stations. Using the new Leroy 39 (2010) classification system on the older siting metadata used by Fall et al. (2011), 40 Menne et al. (2010), and Muller et al. (2012), yields dramatically different results. 41 Both raw and gridded comparisons were performed on the 30 year trends that were 42 calculated for each surveyed station, using temperature data from USHCNv2. Mean 43 temperature trend is indisputably lower for well sited stations than for poorly sited 44 stations. Minimum temperature trend shows the greatest differences between siting 45 classification while maximum temperature trend shows the smallest. 46 Well sited stations consistently show a significantly lower trend than poorly sited 47 stations, no matter which class of station is used for a baseline for comparison, and also 48 when using …