James Anthony Whiteway

Lidar observations of gravity wave activity and Arctic stratospheric vortex core warming

Measurements of stratospheric thermal structure and gravity wave activity have been obtained with a Rayleigh lidar in the Canadian High Arctic at Eureka (80°N, 86°W) during five recent winters. The observations reveal that an annual late December warming of the upper stratosphere occurred in the polar vortex core and was sustained through the winter. Increased gravity wave activity was detected in the vortex jet during the warming. That these two phenomena developed in parallel suggests they are related. It is proposed that increased gravity wave momentum deposition above the jet maximum forced flow into the vortex core where it descended and warmed adiabatically.

Airborne observations of turbulence, mixing, and gravity waves in the tropopause region

[1]xa0In situ observations of small-scale dynamics and compositional structure in the tropopause region are presented. The measurements were made aboard the Grob “Egrett” high-altitude research aircraft above Aberystwyth, Wales, in the summer of 2000. The observations presented here show evidence of mixing of ozone and water vapor in a patch of intense turbulence just above the tropopause. This turbulence is shown to be the result of wind shear above a tropospheric jet stream. The value of the vertical eddy diffusion coefficient in this turbulence is estimated to be 0.9 m2 s−1. It is also shown that wavelike perturbations superimposed on the overall tracer structure can be accounted for by a gravity wave.

Gravity wave interactions around the jet stream

[1]xa0VHF radar measurements have been applied to study the interaction between a mountain wave and an inertia-gravity wave above the jet stream in the tropopause region. The mountain wave was observed to break and generate turbulence at a critical level that was induced by the inertia-gravity wave. This indicates that wave-wave interactions can be an important source of turbulence and, consequently, mixing in the tropopause region.

Enhanced and Inhibited Gravity Wave Spectra

Abstract Balloon measurements were used to investigate gravity waves in the upper troposphere and lower stratosphere above the Canadian high Arctic. The amount of gravity wave activity in the stratosphere was found to be related to particular meteorological conditions that influence the generation and propagation of mountain waves. Enhanced wave activity was observed to occur when there was a small change in wind direction in the troposphere and high wind speed at the ground. These conditions correspond to strong wave generation by flow over the ground of upward-propagating waves that do not encounter critical level filtering. Inhibited wave activity was observed when the wind direction changed by more than 180° in the troposphere or when the wind speed was relatively weak at the ground. These conditions correspond to critical level filtering and weak generation of upward-propagating waves. The vertical wavenumber spectrum of perturbation potential energy was enhanced at all resolved scales when the condi...

Enhanced Arctic stratospheric gravity wave activity above a tropospheric jet

Meteorological balloon measurements were applied to investigate gravity waves in the stratosphere above three weather stations in the Canadian Arctic. It was found that a distinct enhancement in the amount of wave activity occurred at each of the three stations simultaneously while a tropospheric jet stream crossed the Arctic during mid-November of 1996. An interpretation is proposed in which the enhanced wave activity occurs as the tropospheric jet provides conditions that are favourable for the upward propagation of mountain waves. Further propagation into the stratosphere is then facilitated during winter when the tropospheric and stratospheric jets coincide.

Synoptic scale study of the Arctic polar vortex's influence on the middle atmosphere, 1, Observations

[1]xa0We present nightly Rayleigh lidar temperature measurements of the high-latitude middle atmosphere taken at three Arctic sites over similar time periods in midwinter. The four reported case studies depict changes in the thermal structure of the stratosphere and lower mesosphere over a period of days to weeks that can be attributed to movement and interaction of the polar vortex, the Aleutian High, and planetary waves as evidenced from the National Center for Environmental Prediction tropospheric and stratospheric analyses. In cases where substantial (i.e., large horizontal scale) movement of the vortex is observed, it is noted that regional middle atmospheric Arctic temperatures can change by tens of degrees. In other cases, we show that even very subtle (i.e., small horizontal scale) movement of the vortex system over similar timescales can result in notable temperature changes in the regional middle atmosphere. It appears that the observed events are dependant on the location, strength, and structure of the polar vortex and Aleutian High. All of these synoptic scale measurements indicate a change in the local dynamical structure of the middle atmosphere and are discussed in regards to this issue.

Seasonal transition in gravity wave activity during the springtime stratospheric vortex breakdown

Profiles of temperature and wind measured by meteorological balloons are used to examine the changes in gravity wave activity at high latitudes during a final springtime breakdown of the Arctic stratospheric vortex. The measurements show that gravity wave potential energy densities in the lower stratosphere decreased dramatically as the cyclonic wintertime vortex gave way to the weak anticyclonic summertime circulation. The reduction in gravity wave activity after the vortex breakdown is attributed primarily to increased critical level filtering of orographic waves and lowered stratospheric wind speeds.