On the use of constant temperature anemometers in the stratosphere
Abstract
Constant temperature anemometers (CTA) have been used to measure winds in the atmospheric boundary layer for decades. Recently however, instruments like LITOS (Leibniz-Institute Turbulence Observations in the Stratosphere) use them for turbulence soundings in the troposphere and lower stratosphere. LITOS measures wind fluctuations down to the Taylor microscale and retrieves energy dissipation rates by comparing the measurement to a spectral turbulence model. In the stratosphere, the sensor diameter is on the same length scale as the mean free path (five micrometres). Therefore, an influence of flow rarefication on the measurement has to be expected. Within this work, we present an assessment of flow rarefication effects on CTA measurements based on the Direct Simulation Monte Carlo (DSMC) method. We will show that the effects from flow rarefication in the stratosphere are approximately as strong as those from density reduction alone. Furthermore, we will introduce the LITOS measurement technique that is recently only used on descending balloons to mitigate influences of the balloon's wake. Additionally, we will apply our findings from the DSMC calculations to retrieve energy dissipation rates from a LITOS turbulence measurement campaign and explain potential limitations of CTA soundings in the mid-stratosphere.
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E2317S