Showing papers by "David C. Fritts published in 2019"

PMC Turbo: Studying Gravity Wave and Instability Dynamics in the Summer Mesosphere Using Polar Mesospheric Cloud Imaging and Profiling From a Stratospheric Balloon

Abstract: The Polar Mesospheric Cloud Turbulence experiment (PMC Turbo) 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 N. 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 timescales 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 ~2-100 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.

Large-Amplitude Mountain Waves in the Mesosphere Observed on 21 June 2014 During DEEPWAVE: 1. Wave Development, Scales, Momentum Fluxes, and Environmental Sensitivity

Abstract: A remarkable, large-amplitude, mountain wave (MW) breaking event was observed on the night of 21 June 2014 by ground-based optical instruments operated on the New Zealand South Island during the Deep Propagating Gravity Wave Experiment (DEEPWAVE). Concurrent measurements of the MW structures, amplitudes, and background environment were made using an Advanced Mesospheric Temperature Mapper, a Rayleigh Lidar, an All-Sky Imager, and a Fabry-Perot Interferometer. The MW event was observed primarily in the OH airglow emission layer at an altitude of ~82 km, over an ~2-hr interval (~10:30–12:30 UT), during strong eastward winds at the OH altitude and above, which weakened with time. The MWs displayed dominant horizontal wavelengths ranging from ~40 to 70 km and temperature perturbation amplitudes as large as ~35 K. The waves were characterized by an unusual, “saw-tooth” pattern in the larger-scale temperature field exhibiting narrow cold phases separating much broader warm phases with increasing temperatures toward the east, indicative of strong overturning and instability development. Estimates of the momentum fluxes during this event revealed a distinct periodicity (~25 min) with three well-defined peaks ranging from ~600 to 800 m2/s2, among the largest ever inferred at these altitudes. These results suggest that MW forcing at small horizontal scales (<100 km) can play large roles in the momentum budget of the mesopause region when forcing and propagation conditions allow them to reach mesospheric altitudes with large amplitudes. A detailed analysis of the instability dynamics accompanying this breaking MW event is presented in a companion paper, Fritts et al. (2019, https://doi.org/10.1029/2019jd030899).

Large‐Amplitude Mountain Waves in the Mesosphere Observed on 21 June 2014 During DEEPWAVE: 2. Nonlinear Dynamics, Wave Breaking, and Instabilities

Abstract: Weak cross-mountain flow over the New Zealand South Island on 21 June 2014 during the Deep Propagating Gravity Wave Experiment (DEEPWAVE) led to large-amplitude mountain waves in the mesosphere and lower thermosphere. The mesosphere and lower thermosphere responses were observed by ground-based instruments in the lee of the Southern Alps supporting DEEPWAVE, including an Advanced Mesosphere Temperature Mapper, a Rayleigh lidar, an All-Sky Imager, and a Fabry-Perot Interferometer. The character of the mountain wave responses at horizontal scales of ~30–90 km reveals strong “sawtooth” variations in the temperature field suggesting large vertical and horizontal displacements leading to mountain wave overturning. The observations also reveal multiple examples of apparent instability structures within the mountain wave field that arose accompanying large amplitudes and exhibited various forms, scales, and evolutions. This paper employs detailed data analyses and results of numerical modeling of gravity wave instability dynamics to interpret these mountain wave dynamics, their instability forms, scales, and expected environmental influences. Results demonstrate apparently general instability pathways for breaking of large-amplitude gravity waves in environments without and with mean shear. A close link is also found between large-amplitude gravity waves and the dominant instability scales that may yield additional abilities to quantify gravity wave characteristics and effects.

Stratospheric Gravity Wave Products from Satellite Infrared Nadir Radiances in the Planning, Execution, and Validation of Aircraft Measurements during DEEPWAVE

Abstract: Gravity wave perturbations in 15-μm nadir radiances from the Atmospheric Infrared Sounder (AIRS) and Cross-Track Infrared Sounder (CrIS) informed scientific flight planning for the Deep Pro...

Direct Numerical Simulation Guidance for Thorpe Analysis to Obtain Quantitatively Reliable Turbulence Parameters

Abstract: Thorpe analysis has been used to study turbulence in the atmosphere and ocean. It is clear that Thorpe analysis applied to individual soundings cannot be expected to give quantitatively rel...