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Abstract
The Wyoming King Air flew along the 319.5-K isentropic surface and measured ageostrophic winds in the exit region of a polar jet on 8 March 1992. Ageostrophic winds were derived from 1) differences between geostrophic and observed winds and 2) Lagrangian vector acceleration.
The first technique required aircraft-derived Montgomery streamfunctions M and geostrophic winds, which were sensitive to the depiction of overflown terrain. Physically consistent geostrophic winds and M were obtained from manually digitized topographic maps with rough underlying terrain removed from the analysis. The flight was conducted during a cyclogenesis event, so that aircraft-measured M required corrections for unsteady (is- allohypsic) effects. Resulting ageostrophic winds were sensitive to the corrections; halving or doubling the corrections vary ageostrophic wind speeds by as much as 400%.
The second technique required Lagrangian vector accelerators, which assume that a drifting pointer approximates a moving air parcel. Error analysis shows that the Lagrangian pointer technique can measure ageostrophic wind speeds to within several meters per second. Depending on the ageostrophic wind speed, this represents 10%–50% error, which exceeds the accuracy of ageostrophic winds derived from the flat method. This result is significant because it shows that Lagrangian pointer techniques can measure ageostrophic winds without knowledge of overflown terrain and corrections for isallohypsic effects.
Abstract
The Wyoming King Air flew along the 319.5-K isentropic surface and measured ageostrophic winds in the exit region of a polar jet on 8 March 1992. Ageostrophic winds were derived from 1) differences between geostrophic and observed winds and 2) Lagrangian vector acceleration.
The first technique required aircraft-derived Montgomery streamfunctions M and geostrophic winds, which were sensitive to the depiction of overflown terrain. Physically consistent geostrophic winds and M were obtained from manually digitized topographic maps with rough underlying terrain removed from the analysis. The flight was conducted during a cyclogenesis event, so that aircraft-measured M required corrections for unsteady (is- allohypsic) effects. Resulting ageostrophic winds were sensitive to the corrections; halving or doubling the corrections vary ageostrophic wind speeds by as much as 400%.
The second technique required Lagrangian vector accelerators, which assume that a drifting pointer approximates a moving air parcel. Error analysis shows that the Lagrangian pointer technique can measure ageostrophic wind speeds to within several meters per second. Depending on the ageostrophic wind speed, this represents 10%–50% error, which exceeds the accuracy of ageostrophic winds derived from the flat method. This result is significant because it shows that Lagrangian pointer techniques can measure ageostrophic winds without knowledge of overflown terrain and corrections for isallohypsic effects.
Abstract
Freezing rain is commonly caused by overrunning. The typical atmospheric structure and precipitation patterns associated with overrunning and freezing rain suggest a general association between 1) a bright band and 2) a wind-shear layer between the colder air mass near the surface and an overrunning warmer air mass above the frontal boundary. These features were easily detected by a Doppler radar, and their associated thermodynamic structure was documented by an instrumented aircraft in two freezing-rain events near Kansas City, Missouri, in February 1990. The two cases suggest that perhaps freezing rain caused by overrunning has recognizable and easily parameterized Doppler radar signatures that could be incorporated into a freezing-rain detection algorithm. A preliminary algorithm is discussed.
Abstract
Freezing rain is commonly caused by overrunning. The typical atmospheric structure and precipitation patterns associated with overrunning and freezing rain suggest a general association between 1) a bright band and 2) a wind-shear layer between the colder air mass near the surface and an overrunning warmer air mass above the frontal boundary. These features were easily detected by a Doppler radar, and their associated thermodynamic structure was documented by an instrumented aircraft in two freezing-rain events near Kansas City, Missouri, in February 1990. The two cases suggest that perhaps freezing rain caused by overrunning has recognizable and easily parameterized Doppler radar signatures that could be incorporated into a freezing-rain detection algorithm. A preliminary algorithm is discussed.
A winter storm that crossed the continental United States in mid-February 1990 produced hazardous weather across a vast area of the nation. A wide range of severe weather was reported, including heavy snowfall; freezing rain and drizzle; thunderstorms with destructive winds, lightning, large hail, and tornadoes; prolonged heavy rain with subsequent flooding; frost damage to citrus orchards; and sustained destructive winds not associated with thunderstorms. Low-end preliminary estimates of impacts included 9 deaths, 27 injuries, and $120 million of property damage. At least 35 states and southeastern Canada were adversely affected. The storm occurred during the field operations of four independent atmospheric research projects that obtained special, detailed observations of it from the Rocky Mountains to the eastern Great Lakes.
A winter storm that crossed the continental United States in mid-February 1990 produced hazardous weather across a vast area of the nation. A wide range of severe weather was reported, including heavy snowfall; freezing rain and drizzle; thunderstorms with destructive winds, lightning, large hail, and tornadoes; prolonged heavy rain with subsequent flooding; frost damage to citrus orchards; and sustained destructive winds not associated with thunderstorms. Low-end preliminary estimates of impacts included 9 deaths, 27 injuries, and $120 million of property damage. At least 35 states and southeastern Canada were adversely affected. The storm occurred during the field operations of four independent atmospheric research projects that obtained special, detailed observations of it from the Rocky Mountains to the eastern Great Lakes.
