During May and June, 1998 the Arizona Department of Environmental Quality and the U.S. Department of Energy, carried out a collaborative field measurement program in Phoenix, Arizona to study the photochemistry and dispersion of ozone in a relatively hot and dry atmosphere. As part of this effort, meteorological measurements were made at three sites in the Phoenix area: central Phoenix; McDowell Mountain, approximately 35 km to the northeast; and at Superior, approximately 85 km to the east-southeast. The measurements included observations from wind profiling radars, surface meteorology stations, and radiosondes. This paper will focus on observations collected in central Phoenix and at Superior.
On days of intensive observations, radiosondes were launched at 0800, 1000, 1200, 1400, and 1700 LST in central Phoenix and at 1700 LST at Superior. There were 14 such days in the four-week field program, during which conditions were largely undisturbed, and winds were generally light in central Phoenix. The boundary layer typically grew to depths between 2500 m and 3500 m by mid-afternoon. The sequential soundings and light winds permit the computation of surface sensible heat flux from the one-dimensional heat balance. The computed heat fluxes show a fairly orderly increase in the morning to a mid-afternoon maximum of ~600 W m-2, followed by a decrease late in the afternoon. These heat fluxes, while large, are comparable to those found in a recent study in the Mexico City area by Whiteman et al. (1998). Areas with more pronounced topography to the east of Phoenix often experienced stronger afternoon winds, which limits the applicability of the non-advective heat balance at those sites. These data will also be used to explore whether a sloping inversion or other thermodynamic structure contributes to the significant afternoon wind differences observed between central Phoenix and outlying areas.