A New Cross-Platform Instrument for Microstructure Turbulence Measurements

This study developed a new cross-platform instrument for microstructure turbulence measurement (CPMTM) and evaluated its performance. The CPMTM is designed as an “all-in-one” payload that can be easily integrated with a variety of marine instrumentation platforms. The sensors in the CPMTM include two shear probes, a fast-response temperature probe, and an accelerometer for monitoring vibrations. In addition, a custom-designed flexible connection vibration-damping device is used to isolate platform vibrations. To validate the CPMTM performance, a direct comparison was carried out with a reference acoustic Doppler velocimeter in a controlled flume for four background turbulence levels. The results of the comparison show that the velocity spectra measured by the CPMTM and ADV w components are in agreement, which demonstrates the ability of the CPMTM to acquire accurate turbulence data. Furthermore, the CPMTM was integrated into the long-range Sea-Whale 2000 AUV and tested in the northern South China Sea in September 2020. The data collected by the CPMTM show that the measured shear spectrum of the noise reduction agrees well with the empirical Nasmyth spectrum. Turbulent kinetic energy dissipation rates as low as 7 × 10−10 W kg−1 can be resolved. Laboratory and field experiments illustrate that the CPMTM has an extraordinarily low noise level and is validated for turbulence measurements.

Measurement Study of Turbulence in a Tropopause Fold

<p>Tropopause folds are known as regions of intense trace gas exchange between the troposphere and the stratosphere. They occur in upper-level fronts and it is known since the 1970s that turbulence plays a major role in their formation. However, only a limited number of turbulence measurements under these conditions exist. In this study, we present a turbulence sounding in an upper-level front measured with the balloon-borne instrument LITOS (Leibniz-Institute Turbulence Observations in the Stratosphere). This instrument infers turbulent kinetic energy dissipation rates from velocity fluctuations at the Taylor microscale. By using a radiosonde on board of the same balloon, we can observe wind fluctuations across multiple spatial scales.</p><p>In the classical picture of a tropopause fold from the 1970s, we expect turbulence to occur in both shear zones above and below the tropopause jet. For the time of our measurement on 06 August 2016, a similar turbulence distribution is expected due to low Richardson numbers in the respective areas shown by the ECMWF-IFS. Our in-situ turbulence measurement with LITOS, however, shows a different picture: we find turbulence to occur in the upper shear zone above the jet but not in the lower one located in the stratospheric intrusion. In our contribution, we will examine potential reasons for this difference between theoretical expectations and the observation. Furthermore, we will discuss possible implications of the lack of turbulence in the stratospheric intrusion on the exchange of trace gases across the tropopause.</p>