摘要: The Arizona Monsoon Boundary is defined as the boundary separating two distinctly different air masses over Mexico, the southwestern U.S. and the adjacent Pacific during the summer. Its structure and dynamics are examined by cross... 展开 The Arizona Monsoon Boundary is defined as the boundary separating two distinctly different air masses over Mexico, the southwestern U.S. and the adjacent Pacific during the summer. Its structure and dynamics are examined by cross-sectional analysis using 3 different data sources: 1) a time-height cross section, constructed using radiosonde observations, at the time the boundary initially passed through Tucson in 1984; 2) a composite cross section through the boundary, constructed from FNOC analysis; and 3) a cross section through the boundary using high-resolution fields of temperature, moisture, and geopotential height obtained from the VISSR Atmospheric Sounder (VAS). All 3 cross sections showed similar structure. This boundary resembles a mid-latitude front with a distinct and relatively sharp air mass change across the boundary, forced almost entirely by confluence. A direct ageostrophic circulation is produced by this forcing, giving weak ascent on the warm, moist side of the boundary. Gradients and flow associated with the composite boundary are weaker, by a factor of 4, than those associated with strong mid-latitude fronts. However, the VAS cross section suggests that, at times, the strength of the boundary approaches that of middle-latitude fronts. The wind shear suggested by the composite boundary ought to be unstable to baroclinic or barotropic processes. Disturbances developing along the boundary have been observed. Baja California; Monsoons; Fronts meteorology. Theses. (edc) 收起