Dr. Greer currently works on the Global-scale Observations of the Limb and Disk, or GOLD mission. It is a NASA mission of opportunity that measures densities and temperatures in Earth’s thermosphere and ionosphere. GOLD makes these measurements, in unprecedented detail, with an ultraviolet (UV) imaging spectrograph on a geostationary satellite. It launched on 25 January 2018. The goal of the investigation is to provide answers to key elements of an overarching question for Heliophysics science: What is the global-scale response of the thermosphere and ionosphere to forcing in the integrated Sun-Earth system? Dr. Greer is particularly focused on forcing from the lower atmosphere by waves and tides.
Middle Atmospheric Weather Events
The middle atmosphere is a dynamic place- and although the density of the air is much lower than in the troposphere, it still experiences weather. The middle atmosphere comprises both the stratosphere and the mesosphere, approximately 10 km to 100 km (6 miles to 60 miles) above the surface of the Earth. The ‘weather’ in this region is deeply influenced by waves propagating up from the lower atmopshere and energy coming in from above, such solar wind events. This region of the atmosphere has been relatively unexplored until the last 20 years when remote sensing measurement from satellites and ground-based station allowed collection of information on the temperature, winds, cloud formation and minor air constituents.
Planetary Wave Disturbances & Stratopause Warmings
While Sudden Stratospheric Warmings (SSWs) are the most well known event in the polar winter middle atmosphere, smaller more frequent ‘weather’ events also occur. One such event involves a stratopause warming and co-incident cooling of the mesosphere. Katelynn and her collegues have proposed the following dynamics reponsible for these types of events: As large-scale planetary waves propagate up into the upper stratosphere, they interact with the background wind. When these waves break, they deposit their momentum and slow down the nomimal eastward winds causing some vertical air motion as the atmosphere tries re-establish a balanced flow. As the air moves downward, it adiabatically heats and changes the thermal gradients near the stratopause (stratopause warming). The resulting change in the thermal wind and vertical shear in the horizontal winds has the ability to support baroclinic instability. This type of disturbance is the focus of Katelynn’s dissertation.
Work by Immel and Mannucci  has indicated that geomagnetic storms causes a larger effect on the ionospheric TEC (Total Electron Count) in the American sector than anywhere else on the planet, suggesting that there is a longitude dependent (UT) effect which is important for correctly understanding the impact, structure and timing of geomagnetic storms. Katelynn worked to examine the extent to which numerical models appropriately reproduce the observed results, using a model to examine the underlying mechanisms of the longitude-dependent storm enhancements and whether these mid-latitude enhancements are connected to high-latitude changes.
Studies by Goncharenko & Zhang  and Chau et al.  indicate that there observable impacts in the ionosphere during Sudden Stratospheric Warmings (SSWs), suggesting a coupling between the neutral polar winter middle atmosphere and the ionosphere due to changes in planetary waves. Katelynn is working on addressing what kinds of ionospheric anomalies are associated with disturbances of the polar winter middle atmosphere, including major/minor SSWs and USLMs. Are there particular planetary waves and planetary wave breaking regimes associated with ionospheric disturbances? What is the timing and location of ionospheric disturbances in relationship to the neutral middle atmosphere disturbances? For these studies a mixture of observations and models are being used. For the neutral middle atmosphere and lower mesosphere, observations from the MLS and TIMED/SABER satellite measurements have been used in conjunction with assimilated data from MERRA and modeling from SD-WACCM. The E- and F-region ionosphere measurements require incoherent scatter radar data. And finally, solar and geomagnetic parameters will be quantified using several indices: F10.7, Kp and AE.
LiDAR Remote Sensing
LIght Detection And Ranging is a remote sensing technique that is used in a wide variety of environmental monitoring missions. It uses lasers to remotely probe regions of interest and determine different qualities about that area, such as how far away it is, the temperature and the wind speed. Katelynn has designed, operated and troubled-shot several lidar systems. Her Greenland field research involved a high-powered Rayleigh (532 nm) system that could return information from over 80 km (50 miles) high in the atmosphere. She has also worked on 3D wind vector lidar using a random modulation continuous wave technique.
As a graduate student, Katelynn was part of the ASENL research group directed by Professor Jeffrey Thayer at the University of Colorado at Boulder. ARSENL’s research program is rooted in studying the aerospace environment of Earth’s atmosphere and geospace, specifically geophysical fluid dynamics, gas and plasma interactions, thermodynamics, and electrodynamics applied to the upper atmosphere (above 10 km altitude) and geospace.