Temperature dissipation in convective clouds during ACORES and EUREC4A

Abstract

<p>UltraFast Thermometers (UFT’s), developed successively at the Institute of Geophysics, University of Warsaw, allow for airborne measurements of temperature fluctuations in turbulent atmosphere with the resolution better than 1 cm, which provides insight into small-scale turbulent mixing in clouds, atmospheric boundary layer and free atmosphere.</p><p><span>In recent years new versions of UFT thermometers (UFT-2 family) were used in two measurement campaigns: ACORES and EUREC</span><sup><span>4</span></sup><span>A. In ACORES UFT-2 was deployed on the helicopter-borne measurement platform ACTOS used to sample marine stratocumulus clouds with the resolution reaching 3 mm. During the EUREC</span><sup><span>4</span></sup><span>A campaign similar 20 kHz temperature time series have been collected with the UFT-2b deployed onboard the BAS Twin Otter aircraft (average speed of </span><span>6</span><span>0 m/s) in the subtropical low atmosphere, in and between trade wind warm cumulus clouds. Data, resolving scales down the dissipation range,</span><span> allow to</span> <span>estimate</span> <span>directly</span> <span>the temperature </span><span>dissipation rate (TD) in cloud interiors, cloud shells, air spaces between the clouds, </span><span>and</span><span> in the atmospheric boundary layer.</span></p><p><span><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.bcad0e8be76268767790561/sdaolpUECMynit/2202SME&app=m&a=0&c=f286e6c560bb8ccb42931ce4fe1a4934&ct=x&pn=gnp.elif&d=1" alt=""></span></p><p><span>Fig. 1. Example of the UFT-2 0.5 s long measurements from EUREC<sup>4</sup>A campaign: high-resolution plots of temperature (red) and TD (blue) before and during penetration through a cumulus cloud.</span></p><p>Until now, no experimental data on temperature dissipation in free atmosphere and in clouds from in situ measurements have ever been published. Such data may help to understand cloud microphysical processes with phase changes. Classically, during turbulent mixing of air masses, temperature is considered a passive scalar. In clouds, in the course of condensation/evaporation heat is released/absorbed, which may affect fine-scale fluctuations of temperature. Thus, statistical properties of temperature dissipation should differ from situations in which the temperature is just a passive scalar. Examples of temperature fluctuations and associate TD records (see Fig. 1), characteristic to the various atmospheric conditions, will be presented and discussed.</p><p>Acknowledgements: This project has received funding from Polish National Science Center (NCN) under grant agreement 2018/30/M/ST10/00674.</p>