Articles | Volume 34, issue 12
Ann. Geophys., 34, 1209–1229, 2016
Ann. Geophys., 34, 1209–1229, 2016

Regular paper 16 Dec 2016

Regular paper | 16 Dec 2016

Derivation of turbulent energy dissipation rate with the Middle Atmosphere Alomar Radar System (MAARSY) and radiosondes at Andøya, Norway

Qiang Li1, Markus Rapp1,a, Anne Schrön2, Andreas Schneider2, and Gunter Stober2 Qiang Li et al.
  • 1Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, 82234 Oberpfaffenhofen, Germany
  • 2Leibniz-Institut für Atmosphärenphysik, 18225 Kühlungsborn, Germany
  • aalso at: Meteorologisches Institut München, Ludwig-Maximilians-Universität München, Munich, Germany

Abstract. We present the derivation of turbulent energy dissipation rate ε from a total of 522 days of observations with the Middle Atmosphere Alomar Radar SYstem (MAARSY) mesosphere–stratosphere–troposphere (MST) radar running tropospheric experiments during the period of 2010–2013 as well as with balloon-borne radiosondes based on a campaign in the summer 2013. Spectral widths are converted to ε after the removal of the broadening effects due to the finite beam width of the radar. With the simultaneous in situ measurements of ε with balloon-borne radiosondes at the MAARSY radar site, we compare the ε values derived from both techniques and reach an encouraging agreement between them. Using all the radar data available, we present a preliminary climatology of atmospheric turbulence in the UTLS (upper troposphere and lower stratosphere) region above the MAARSY site showing a variability of more than 5 orders of magnitude inherent in turbulent energy dissipation rates. The derived ε values reveal a log-normal distribution with a negative skewness, and the ε profiles show an increase with height which is also the case for each individual month. Atmospheric turbulence based on our radar measurements reveals a seasonal variation but no clear diurnal variation in the UTLS region. Comparison of ε with the gradient Richardson number Ri shows that only 1.7 % of all the data with turbulence occur under the condition of Ri < 1 and that the values of ε under the condition of Ri < 1 are significantly larger than those under Ri > 1. Further, there is a roughly negative correlation between ε and Ri that is independent of the scale dependence of Ri. Turbulence under active dynamical conditions (velocity of horizontal wind U > 10 m s−1) is significantly stronger than under quiet conditions (U < 10 m s−1). Last but not least, the derived ε values are compared with the corresponding vertical shears of background wind velocity showing a linear relation with a corresponding correlation coefficient r = 58 % well above the 99.9 % significance level. This implies that wind shears play an important role in the turbulence generation in the troposphere and lower stratosphere (through the Kelvin–Helmholtz instability).

Short summary
Turbulence is an essential process in the atmosphere and ocean. Clear-air turbulence is a well-known threat for the safety of aviation. Using a powerful MST radar, we detected turbulence and compared it with the results from radiosondes. The correlation between turbulence and background conditions, e.g., Richardson number and wind shears, is determined. There is a nearly negative correlation between turbulence and Richardson number independent of the length scale over which it was calculated.