Structure and dynamics of the Arizona monsoon boundary

The structure and dynamics of the Arizona monsoon boundary, defined as the boundary separating two distinctly different air masses over Mexico and the adjacent Pacific during the summer, are analyzed. The cross-sectional analysis was based on the following three data sources: a composite cross section through the boundary, constructed from the Fleet Numerical Oceanography Center analysis for 1985; a time-height cross section, obtained using radiosonde observations at the time the boundary passed through Tucson in 1984; and a cross section through the boundary of July 22, 1985, using high-resolution fields of temperature, moisture, and geopotential height obtained from the VISSR Atmospheric Sounder. All three sources yielded similar structure, showing that the Arizona monsoon boundary resembles a midlatitude front forced almost entirely by confluence. The possible role this frontlike system may play in the development of disturbances in the southwestern United States during summer is discussed.