Observations of Neutral Profiles of Wind Speed and Specific Humidity

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Reliable methods to estimate local sensible and la- tent heat flux at a point using micro-meteorological or turbulence data are available (e.g., Brutsaert. 1982).
Journal of the MeteorologicalSociety of Japan, Vol. 78, No. 6, pp. 719-730, 2000

Observations

of Neutral Above

Profiles

of Wind

a Gently

Rolling

By Jun Terrestrial Environment

and

Specific

Humidity

Landsurface

Asanuma

Research Center, University of Tsukuba, Tsukuba, Japan Nelson

SIMEPAR-Parana

Speed

719

L. Dias

Meteorological System, Centeo Politecnico da UFPR, PR Brazil William

P. Kustas

Hydrology Laboratory, Agricultural Research Service, US Department of Agriculture, Maryland, USA and Wilfried

Brutsaert)

School of Civil and Environmental Engineering, Cornell University, New York, USA (Manuscript

received 4 June 1999, in revised form 28 July 2000) Abstract

Analyses were made of wind speed and specific humidity profiles under neutral conditions obtained by radiosoundings over the gently rolling terrain of the Little Washita Basin, Oklahoma. Inspection of the wind speed profiles showed that the regional (scale of 1 to 10km) roughness of this basin was z0=0.45 f 0.21m, while the displacement height, do, was found to be 8.9m. The logarithmic layer of wind speed was observed to occupy the range, (38f43)z.(>-0.0059 0.28+(-)0.75 0.28+(0.0059-0)0.75

where (0-z0/L. For strictly neutral conditions, 1m (=0 is required in (2), which is simultaneously equivalent to L=0 with Hv=0 or u*=oc. As mentioned, such strictly neutral conditions occur very rarely in the real atmosphere. Rather, for practical purposes, it is usually permissible to take a certain range of L as "practically neutral", where L is large enough so that the stability correction term, Wm(1), is negligibly small compared to the logarithmic term, In ((z-d0) /z0) in (2). If the permissible error caused by taking a profile as neutral is defined as In z

profiles.

Vol. 78, No. 6

the

north

in degrees.

Table

2. Criteria

over

the

of atmospheric

lowest

neutrality.

50m.

for -0.0059>C>-15.025 for (