Seasonal Evolution of the Surface Radiation Balance in the City of São Paulo Amauri Pereira de Oliveira Jacyra Soares Grupo de Micrometeorologia Departamento de Ciências Atmosféricas – IAG/USP

City Climate The characterization of the climate in city is a very complex task due to the large heterogeneity of the land use and topography (Oke, 1982; Oke et al., 1999, Gambi et al., 2000).

Land use of São Paulo SOURCE:ATLAS AMBIENTAL DO MUNICÍPIO DE SÃO PAULO

Topography of São Paulo Area = 50 km x 50 km centered at CUASO (GTOP)

Objective Estimate the components of radiation balance at the surface; Seasonal evolution of the net radiation at the surface for São Paulo city.

Part 1 Data set, sites and sensors

Data set 7 years 5 years 9 years

Localization of observations CUASO – IAG Micrometeorológical Plataform, University Campus Armando Salles de Oliveira at Butantã, at 744 m above the mean sea level ( ' S, ' W); PEFI – IAG Meteorological Station, Parque Estadual das Fontes do Ipiranga at Parque do Estado, at 780 m above the mean sea level ( ' S, W).

Localization - Regional land use CUASO PEFI 20 km Tietê river

Micrometeorological Platform - CUASO Net radiation components Net Radiometer Kipp Zonen Atmospheric long wave emission Pyrgeometer Eppley

PEFI Surface Temperature Air Temperature

Part 2 Solar radiation effects on pyrgeometer Pyrgeometer model PIR Eppley

Schematic of wiring and connections for the Eppley PIR

Manufacturer recommendation The value of s 1 is provided by the manufacturer is V W -1 m -2.

Fairall, C. W., Persson, P. O. G., Bradley, E. F., Payne, R. E. and Anderson, S. P., 1998: A New Look at Calibration and Use of Eppley Precision Infrared Radiometers. Part I: Theory and Application, Journal of Atmospheric and Oceanic Technology, 15, 1229 – According to Fairall et al (1998) the error ~ 5.5 % using manufacturer recommendation. Too much for radiation balance studies at the surface.

Dome Effect Correction proposed by Fairall et al. (1998) Where L 1 DW is the corrected value of longwave radiation, V is the thermopile voltage, T c and T D are, respectively, the case and dome temperatures, s 0 and B are calibration factors which depend of the sensor direct calibration.

Sensor temperature

Problem of Fairall corrections Requires T C and T D measurements; Due to data acquisition limitations measurements of dome and case temperatures started only in October of 2003; Measurements of L DW started in September 1997.

Perez Allados-Arboledas (1999) Where is the corrected long wave radiation L 2 DW is the long wave radiation obtained using expression proposed by manufacturer, I DW is the global solar radiation in Wm -2 and V is the wind intensity in ms -1.

Longwave atmospheric emission Fairall et al. (1998) Manufacturer Perez and Allados-Arboledas (1999)

Corrections for pyrgeometer PIR Correction proposed by Perez and Allados- Arboledas (1999) was applied to estimate the monthly averaged longwave atmospheric emission measured by the pyrgeometer PIR at CUASO using: –Diurnal evolution of monthly averaged wind speed from CETESB (Oliveira et al., 2003); –Monthly averaged values of global solar radiation measured in CUASO.

PEFI representativity Part 3

Monthly averaged Air temperature Sea Breeze

Hourly values of Temperature Sea Breeze

Surface longwave emission

Reflected solar radiation

Part 4 Seasonal evolution of radiation balance components

Global solar radiation ( I DW ) Reflected solar radiation ( I UP ) Top

Surface Temperature ( T G ) at PEFI Surface longwave emission ( L UP )

Seasonal Evoluation of net radiation

Conclusion Seasonal evolution of the monthly average hourly values of net radiation indicates: –Nighttime maximum in winter (June) of +50 W.m -2 and a nighttime minimum in summer (December) near zero; –Daytime maximum in the summer (December) of -500 W.m -2 and a daytime minimum in winter (June) of -370 W.m -2 ;

Acknowledgement CNPq and FAPESP; IAG/USP meteorological station at PEFI.