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  • Author or Editor: Gregory D. Nastrom x
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William H. Jasperson
and
Gregory D. Nastrom

Abstract

Comparison between in situ aircraft observations of temperature and National Meteorological Center and Global Weather Central analysis fields of temperature is presented for a continental and oceanic flight route. The standard deviations of the temperature differences over several hundred flights are found to be 2.5 and 3.5°C for the continental and oceanic route, respectively. A bias towards warm temperatures of about 0.85°C for the analysis fields was found for the oceanic route. Only small differences are found between the NMC and GWC analysis field temperatures.

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William H. Jasperson
,
Gregory D. Nastrom
,
Richard E. Davis
, and
James D. Holdeman

Abstract

A climatology of high-altitude cloud encounters using data obtained between 1975 and 1979 from commercial airliners participating in the Global Atmospheric Sampling Program (GASP) is presented. The statistics are based on three different measures of cloudiness derived from the GASP data set. This climatology depicts the seasonal, latitudinal and altitudinal variation in the cloudiness parameters, as well as differences in the high-altitude cloud structure attributed to cyclone- and convective cloud-generation mechanisms. A qualitative agreement was found between the latitudinal distribution of cloud cover derived from the GASP data and satellite-derived high-altitude cloud statistics available in the literature. Relationships between the three different measures of cloudiness and the relative vorticity at high altitudes, stratified by season, latitude and distance from the tropopause are also presented. In midlatitudes, for example, the average cloudiness, when stratified by the sign of the relative vorticity, exhibits a seasonal cycle with the 1argest differences occurring in the layer 0–1.5 km below the tropopause. Seasonal and latitudinal patterns can also be seen in the other cloudiness parameters.

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Anthony R. Hansen
,
Gregory D. Nastrom
,
Jason A. Otkin
, and
Frank D. Eaton

Abstract

The effect of deep convection on the intensities of gravity waves and turbulence during the summer at White Sands, New Mexico, is investigated using 50-MHz mesosphere–stratosphere–troposphere (MST) radar observations and surface weather reports. Radar data taken at 3-min intervals from the summers of 1991 through 1996 (with occasional gaps of varying length) are used to construct hourly means, medians, and standard deviations of wind speed, spectral width ( σ 2 turb ), and backscattered power calibrated as the refractivity turbulence structure constant ( C 2 n ). The hourly variance of the vertical velocity σ 2 w is used as an indicator of high-frequency gravity wave intensity. Surface observations taken near the radar site are used to identify periods marked by convection at or near the radar. During cases in which no convection is reported, the median hourly σ 2 w is nearly constant with altitude (about 0.04 m2 s−2 below and 0.03 m2 s−2 above the tropopause). Values of σ 2 w , C 2 n , and σ 2 turb are significantly enhanced from no-convection cases to thunderstorm cases. Largest increases are about 12 dB relative to the no-convection cases at about 11 km for σ 2 w , about 9.5 km for σ 2 turb , and about 7.5 km for C 2 n . The relatively lower height for the maximum of C 2 n is likely due to the influence of humidity advected upward during convection on the mean gradient of the refractive index. The probability density distributions of C 2 n and σ 2 turb near their levels of maximum enhancement are unimodal, with the modes steadily increasing with increasing proximity of convection. However, the probability density distribution of σ 2 w is bimodal in all instances, suggesting that there can be enhanced wave activity even when visible convection is not present and that the presence of a thunderstorm at the station does not necessarily indicate greatly enhanced wave activity.

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