Aircraft measurements of gravity waves in the upper troposphere and lower stratosphere during the START08 field experiment

摘要

This study analyzes in situ airborne measurements from the 2008Stratosphere–Troposphere Analyses of Regional Transport (START08) experimentto characterize gravity waves in the extratropical upper troposphere andlower stratosphere (ExUTLS). The focus is on the second research flight(RF02), which took place on 21–22 April 2008. This was the first airbornemission dedicated to probing gravity waves associated with strongupper-tropospheric jet–front systems. Based on spectral and wavelet analysesof the in situ observations, along with a diagnosis of the polarizationrelationships, clear signals of mesoscale variations with wavelengths~ 50–500 km are found in almost every segment of the 8 hflight, which took place mostly in the lower stratosphere. The aircraftsampled a wide range of background conditions including the region near thejet core, the jet exit and over the Rocky Mountains with clear evidence ofvertically propagating gravity waves of along-track wavelength between 100and 120 km. The power spectra of the horizontal velocity components andpotential temperature for the scale approximately between ~ 8 and ~ 256 km display an approximate −5/3 power law inagreement with past studies on aircraft measurements, while the fluctuationsroll over to a −3 power law for the scale approximately between~ 0.5 and ~ 8 km (except when this part ofthe spectrum is activated, as recorded clearly by one of the flightsegments). However, at least part of the high-frequency signals with sampledperiods of ~ 20–~ 60 s and wavelengths of~ 5–~ 15 km might be due to intrinsicobservational errors in the aircraft measurements, even though thepossibilities that these fluctuations may be due to other physical phenomena(e.g., nonlinear dynamics, shear instability and/or turbulence) cannot becompletely ruled out.