Some measurements on undercutting cold air

Abstract

S m YFrom time series of closely-spaced upper-wind (pilot-balloon) measurements in the rear of synoptic lines of wind shift and cooling, the configuration of the elevated wind-shear layer and the strength of the flow beneath are deduced. The height of the shear layer does not rise uniformly with time, but at one stage remains constant or decreases, before resuming a sustained rise. It is demonstrated by the method of dynamic similarity that this phenomenon is broadly the counterpart of the friction head on density surges in stratified liquids.Cumulative inflow into the advancing wedge of cold air is compared with the total mass in the cold air wedge and found to be generally in excess of this, the exceptions occurring with sea-breezes or analogous phenomena on a larger scale (coastal fronts). In one case where sufficient observations are available, vertical velocities are computed. The excess inflow is shown to be associated with a vertical circulation involving considerable mass transfer upward across the shear zone.

marine air invasion of the Pacific Coast a problem analysis

“…There appear to be three types of sea breeze reported in the literature. The first is the classical air-mass front as reported by Koschmieder (1935), Berson (1958), Wallington (1959Wallington ( , 1965, Simpson (1965), Frizzola and Fisher (1963), Leopold (1949), and Rao (1955), in which the sea-breeze front is characterized by a sharp temperature fall, humidity rise, and sharp wind-velocity change.…”

“…The depth of the sea breeze is greater in onshore flow conditions than in offshore flow conditions. For flow parallel to the coast, certain features may be inferred from Berson's (1958) work to complement the above cited papers. With an anticyclone offshore, the depth of the sea breeze is shallow and the front intense, in general, similar to the conditions for offshore gradient flow.…”

“…The third type of sea-breeze front is that of the cool change described principally by Lowry (1962) and Berson (1958). This sea-breeze front is characterized by a sustained cooling and humidity rise and no wind-shear line.…”

“…Because the sea breeze is superimposed on the monsoon, this description is equally valid for the monsoon. Rao (1955), Frizzola and Fisher (1963), and Berson (1958) have described an inland wind maximum in the sea-breeze flow. This maximum is noticeably absent in the Pacific coast sea breeze.…”

Vertical Structure of a Nonprecipitating Cold Frontal Head as Revealed by Raman Lidar and Wind Profiler Observations

“…Several measurements indicated that the leading edge of some cold fronts showed a correspondence to gravity (density) currents (Berson 1958;Clarke 1961;Hobbs and Persson 1982;Carborne 1982;Garratt and Physick 1986). A gravity current is a mass of highdensity (cold) fluid that flows along a horizontal bottom, displacing ambient lesser-density (warmer) fluid (e.g., Glickman 2000).…”