The research is to study vertical coupling in the wintertime polar regions between the stratosphere and mesosphere and to investigate the mechanisms leading to significant disturbances of the polar wintertime mesosphere during strong baroclinic conditions in the stratosphere. The project will explore and study these baroclinic structures in detail by utilizing global temperature measurements of the stratosphere and mesosphere from satellite observations combined with extensive ground-based observations. Furthermore, empirical and numerical models will be employed to reproduce the observed phenomena and develop a more complete physical understanding of the vertical coupling, planetary wave activity, and mechanistic processes.
The ground-based measurements will include Rayleigh LIDAR measurements from Greenland and hydroxyl temperatures from interferometric measurements in Arctic and Antarctic. In addition to the atmospheric observations, the PIs will combine their observations with atmospheric community models such as the Whole-Atmosphere Climate Community Model (WACCM).
, AGS 0940174, was a four-year project with activities performed within the Departments of Aerospace Engineering Sciences and Atmospheric and Oceanic Sciences at the University of Colorado, and at NCAR’s High Altitude Observatory at NCAR in Boulder. The project was to compile observational characteristics of anomalous temperature enhancements in the polar winter middle atmosphere (stratosphere / mesosphere, 10-100 km altitude) and determine through numerical models the dynamical mechanisms responsible for this strange thermal structure. The strongest disturbance to the middle atmosphere is a major Sudden Stratospheric Warming (SSW), which can alter the entire atmospheric column, from the troposphere to the thermosphere on a planetary scale. However, we have established through this research that anomalous temperature disturbances in the middle atmosphere (called Upper Stratosphere Lower Mesosphere USLM disturbances) associated with planetary wave breaking are more frequent than the major SSWs and may also be prognosticators for these more extensive disturbances. Ground-based and satellite-borne observations, assimilated data and numerical models have been used in this study to develop criteria for identifying USLM disturbances, establish their climatology, and examine their development within the context of breaking planetary waves, wave-mean flow interactions, vertical indirect circulations and the potential to support baroclinic instabilities in the polar winter middle atmosphere. The tangible impacts of this work contribute to advancing the field of atmospheric physics by providing a deeper understanding of the mechanisms for natural variability in the polar winter middle atmosphere. This research will contribute to an overarching goal of the community to improve prediction of the large scale restructuring of the polar vortex during active winters. A need that may impact how tropospheric storm systems develop, track and evolve at polar and middle latitudes. The outcomes of this research include: Identified the USLM thermal structure as a synoptic-scale feature of polar wintertime disturbances that are dynamically driven by planetary waves form the troposphere Established criteria for identifying USLM events in observations, assimilated data sets and models; showing that Whole Atmosphere Community Climate Model (WACCM) spontaneously and internally generates USLMs that match the observed characteristics Developed climatologies detailing frequency of occurrence, duration, geographical preference, composited structure and morphology in assimilated data and the WACCM model in both hemispheres Determined breaking planetary waves near 49 km altitude could produce conditions to support baroclinic instability on the East side of the polar vortex. This is established as the likely mechanism for USLM formation leading to front-like behavior in the polar middle atmosphere Identified critical relationships of USLM disturbances with minor and major SSWs that may assist in the prediction of major SSWs. Proposed an initial iteration of dynamics-based definitions for the occurrence of SSWs. This will advance ability to predict large-scale disturbances of the entire atmospheric column from the troposphere to the thermosphere and ionosphere Associated mesosphere coolings (separated mesopause) and stratopause folds with USLM events Finally this project has led to the training and development of two PhD students, Jeff France and Katelynn Greer. Dr. France did a comprehensive study of the Earth’s stratopause by developing climatologies based on satellite measurements ( NASA missions: MLS, SABER, and HIRDLS) along with WACCM simulations. Zonal asymmetries in stratopause temperature and height were found to be directly related to the location of the polar vortices and anticyclonic circulation systems. Dr. Greer researched anomalous temperature excursions in the polar winter middle atmosphere using ground-based and space-based measurements, assimilated data sets, and numerical modeling to characterize and simulate the feature and its related processes.
