Abstract
Abstract. This study analyzes in situ airborne measurements from the 2008 Stratosphere–Troposphere Analyses of Regional Transport (START08) experiment to characterize gravity waves in the extratropical upper troposphere and lower stratosphere (ExUTLS). The focus is on the second research flight (RF02), which took place on 21–22 April 2008. This was the first airborne mission dedicated to probing gravity waves associated with strong upper-tropospheric jet–front systems. Based on spectral and wavelet analyses of the in situ observations, along with a diagnosis of the polarization relationships, clear signals of mesoscale variations with wavelengths ~ 50–500 km are found in almost every segment of the 8 h flight, which took place mostly in the lower stratosphere. The aircraft sampled a wide range of background conditions including the region near the jet core, the jet exit and over the Rocky Mountains with clear evidence of vertically propagating gravity waves of along-track wavelength between 100 and 120 km. The power spectra of the horizontal velocity components and potential temperature for the scale approximately between ~ 8 and ~ 256 km display an approximate −5/3 power law in agreement with past studies on aircraft measurements, while the fluctuations roll over to a −3 power law for the scale approximately between ~ 0.5 and ~ 8 km (except when this part of the spectrum is activated, as recorded clearly by one of the flight segments). However, at least part of the high-frequency signals with sampled periods of ~ 20–~ 60 s and wavelengths of ~ 5–~ 15 km might be due to intrinsic observational errors in the aircraft measurements, even though the possibilities that these fluctuations may be due to other physical phenomena (e.g., nonlinear dynamics, shear instability and/or turbulence) cannot be completely ruled out.
Highlights
One of the challenges to understanding the extratropical upper troposphere and lower stratosphere (ExUTLS) is that dynamical processes with a wide range of scales occur in the region
Relevant work includes Nastrom and Fritts (1992) and Fritts and Nastrom (1992), who used commercial aircraft measurements to infer the different sources of gravity waves
The current study focuses on the second research flight (RF02), which was the first airborne mission dedicated to probing gravity waves associated with strong upper-tropospheric jet–front systems and high topography
Summary
One of the challenges to understanding the extratropical upper troposphere and lower stratosphere (ExUTLS) is that dynamical processes with a wide range of scales occur in the region. Mesoscale gravity waves with horizontal wavelengths of ∼ 50–∼ 500 km are known to occur in the vicinity of unbalanced upper-tropospheric jet streaks and on the cold-air side of surface frontal boundaries (Uccellini and Koch, 1987; Plougonven and Zhang, 2014). Relevant work includes Nastrom and Fritts (1992) and Fritts and Nastrom (1992), who used commercial aircraft measurements to infer the different sources of gravity waves (convections, front, topography, and jet streaks) They found that mesoscale variances of horizontal wind and temperature were large at the jet–front vicinity regions.
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