A Pronounced Upper-Tropospheric Warm Anomaly Encountered by the NOAA G-IV Aircraft in the Vicinity of Deep Convection

Abstract

Recent flights near deep convection by the National Oceanic and Atmospheric Administration's Gulfstream-IV surveillance aircraft have occasionally experienced significant positive temperature anomalies that sometimes impact the aircraft performance. One such event occurred over the Bahamas on 23 August 1999. During a 20-s time period, when the plane was cruising at an altitude of 175 hPa, the flight-level ambient temperature rose 15°C and returned to ambient values, concurrent with significant fluctuations in the horizontal and vertical winds. Large temperature anomalies such as that reported here can cause the avionics on the aircraft to compensate with a sudden decrease in air speed and a loss of altitude. Possible explanations for this anomaly include instrument error and convectively forced gravity waves or upper-level subsidence.