Winds and temperatures of the Arctic middle atmosphere during January measured by Doppler lidar
Abstract. We present an extensive data set of simultaneous temperature and wind measurements in the Arctic middle atmosphere. It consists of more than 300 h of Doppler Rayleigh lidar observations obtained during three January seasons (2012, 2014, and 2015) and covers the altitude range from 30 km up to about 85 km. The data set reveals large year-to-year variations in monthly mean temperatures and winds, which in 2012 are affected by a sudden stratospheric warming. The temporal evolution of winds and temperatures after that warming are studied over a period of 2 weeks, showing an elevated stratopause and the reformation of the polar vortex. The monthly mean temperatures and winds are compared to data extracted from the Integrated Forecast System of the European Centre for Medium-Range Weather Forecasts (ECMWF) and the Horizontal Wind Model (HWM07). Lidar and ECMWF data show good agreement of mean zonal and meridional winds below  ≈ 55 km altitude, but we also find mean temperature, zonal wind, and meridional wind differences of up to 20 K, 20 m s−1, and 5 m s−1, respectively. Differences between lidar observations and HWM07 data are up to 30 m s−1. From the fluctuations of temperatures and winds within single nights we extract the potential and kinetic gravity wave energy density (GWED) per unit mass. It shows that the kinetic GWED is typically 5 to 10 times larger than the potential GWED, the total GWED increases with altitude with a scale height of  ≈ 16 km. Since temporal fluctuations of winds and temperatures are underestimated in ECMWF, the total GWED is underestimated as well by a factor of 3–10 above 50 km altitude. Similarly, we estimate the energy density per unit mass for large-scale waves (LWED) from the fluctuations of nightly mean temperatures and winds. The total LWED is roughly constant with altitude. The ratio of kinetic to potential LWED varies with altitude over 2 orders of magnitude. LWEDs from ECMWF data show results similar to the lidar data. From the comparison of GWED and LWED, it follows that large-scale waves carry about 2 to 5 times more energy than gravity waves.
Gravity waves excited during a minor sudden stratospheric warming
Abstract. An exceptionally deep upper-air sounding launched from Kiruna
airport (67.82∘ N, 20.33∘ E) on 30 January 2016 stimulated
the current investigation of internal gravity waves excited during a minor
sudden stratospheric warming (SSW) in the Arctic winter 2015/16. The analysis
of the radiosonde profile revealed large kinetic and potential energies in
the upper stratosphere without any simultaneous enhancement of upper
tropospheric and lower stratospheric values. Upward-propagating
inertia-gravity waves in the upper stratosphere and downward-propagating
modes in the lower stratosphere indicated a region of gravity wave generation
in the stratosphere. Two-dimensional wavelet analysis was applied to vertical
time series of temperature fluctuations in order to determine the vertical
propagation direction of the stratospheric gravity waves in 1-hourly
high-resolution meteorological analyses and short-term forecasts. The
separation of upward- and downward-propagating waves provided further evidence
for a stratospheric source of gravity waves. The scale-dependent
decomposition of the flow into a balanced component and inertia-gravity waves
showed that coherent wave packets preferentially occurred at the inner edge
of the Arctic polar vortex where a sub-vortex formed during the minor SSW.

On the occurrence and evolution of extremely high temperatures at the polar winter stratopause — A GCM study
Sudden warmings in the stratopause region are a well known phenomenon in middle atmosphere dynamics. In this study, these stratopause warmings are analyzed using a ten year integration of the Berlin Climate Middle Atmosphere Model. The good spatial and temporal resolution of the model allows to investigate the main properties on a statistical basis. It turns out that strong stratopause warmings occur in almost each northern hemisphere winter. The associated temperature maximums and the descent of the stratopause agree very well with observed events. Two selected warmings are compared in terms of EP flux diagnostics and planetary wave amplitudes to study the links between stratopause events and (major) warmings in the lower/middle stratosphere. Only with supply of upward propagating wave energy from the troposphere and lowest stratosphere, stratopause warmings develop to lower stratospheric warmings.