Radiation fluxes in a business district of Shanghai, China

摘要

Radiative fluxes are key drivers of surface-atmosphere heat exchanges in cities. Here the first year-long (December 2012 – November 2013) measurements of the full radiation balance for a dense urban site in Shanghai are presented, collected with a net radiometer CNR4 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 is 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 (11:00 -13:00 LST) clear sky surface albedo (α) is 0.128, 0.141, 0.143 and 0.129 for winter, spring, summer and autumn, respectively. α varies with solar elevation and azimuth angle due to 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 NARP/SUEWS land surface model reproduces the radiation components at this site well, 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.