The Polar Mesospheric Cloud Turbulence (PMC Turbo) experiment was designed to observe and quantify the dynamics of small‐scale gravity waves (GWs) and instabilities leading to turbulence in the upper mesosphere during polar summer using instruments aboard a stratospheric balloon. The PMC Turbo scientific payload comprised seven high‐resolution cameras and a Rayleigh lidar. Overlapping wide and narrow camera field of views from the balloon altitude of ~38 km enabled resolution of features extending from ~20 m to ~100 km at the PMC layer altitude of ~82 km. The Rayleigh lidar provided profiles of temperature below the PMC altitudes and of the PMCs throughout the flight. PMCs were imaged during an ~5.9‐day flight from Esrange, Sweden, to Northern Canada in July 2018. These data reveal sensitivity of the PMCs and the dynamics driving their structure and variability to tropospheric weather and larger‐scale GWs and tides at the PMC altitudes. Initial results reveal strong modulation of PMC presence and brightness by larger‐scale waves, significant variability in the occurrence of GWs and instability dynamics on time scales of hours, and a diversity of small‐scale dynamics leading to instabilities and turbulence at smaller scales. At multiple times, the overall field of view was dominated by extensive and nearly continuous GWs and instabilities at horizontal scales from ~2 to 100 km, suggesting sustained turbulence generation and persistence. At other times, GWs were less pronounced and instabilities were localized and/or weaker, but not absent. An overview of the PMC Turbo experiment motivations, scientific goals, and initial results is presented here.
We report a detailed analysis of atmospheric stabilities in the mesopause region (85–100 km) based on over 2,000 hr of high‐resolution temperature and horizontal wind measurements made with a Na lidar at the Andes Lidar Observatory, located in Cerro Pachón, Chile (30.25°S, 70.74°W). The square of Brunt–Väisälä frequency and the Richardson number are calculated, and occurrence probabilities of convective and dynamic instabilities are derived. An approach to assess the biases due to measurement uncertainties is used to obtain more accurate occurrence probabilities. The overall occurrence probabilities of convective and dynamic instabilities are 2.7% and 6.7%, respectively. High‐, medium‐, and low‐ frequency gravity wave (GW) contributions to these probabilities are isolated, which show that the high‐frequency GWs contribute most but simultaneous presence of high‐ and medium frequency GWs is much more effective in increasing the probabilities. Convective and dynamic instabilities are mainly generated because of the joint effect of different‐scale GWs. Isolated parts of GWs have much less contribution to the generation of both convective and dynamic instabilities. The dynamic instability is mainly contributed from less stable stratification and large wind shear together. Either factor can lead to about 15% of dynamic instability.
more » « less- NSF-PAR ID:
- 10373636
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 127
- Issue:
- 9
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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