Radiation Fluxes in a Business District of Shanghai, China

Abstract

AbstractRadiative fluxes are key drivers of surface–atmosphere heat exchanges in cities. Here the first yearlong (December 2012–November 2013) measurements of the full radiation balance for a dense urban site in Shanghai, China, are presented, collected with a CNR4 net radiometer mounted 80 m above ground. Clear-sky incoming shortwave radiation K↓ (median daytime maxima) ranges from 575 W m−2 in winter to 875 W m−2 in spring, with cloud cover reducing the daily maxima by about 160 W m−2. The median incoming longwave radiation daytime maxima are 305 and 468 W m−2 in winter and summer, respectively, with increases of 30 and 15 W m−2 for cloudy conditions. The effect of air quality is evident: haze conditions decrease hourly median K↓ by 11.3%. The midday (1100–1300 LST) clear-sky surface albedo α is 0.128, 0.141, 0.143, and 0.129 for winter, spring, summer, and autumn, respectively. The value of α varies with solar elevation and azimuth angle because of the heterogeneity of the urban surface. In winter, shadows play an important role in decreasing α in the late afternoon. For the site, the bulk α is 0.14. The Net All-Wave Radiation Parameterization Scheme/Surface Urban Energy and Water Balance Scheme (NARP/SUEWS) land surface model reproduces the radiation components at this site well, which is a promising result for applications elsewhere. These observations help to fill the gap of long-term radiation measurements in East Asian and low-latitude cities, quantifying the effects of season, cloud cover, and air quality.