Current and Past Research Projects

 Abstract:

Satellite data combined with a reanalysis product is used to identify the thermodynamic and dynamic controls that govern mesoscale convective systems (MCSs). Composites are made of MCSs occurring within the tropics (30ºS to 30ºN) during 2014-2016, excluding those associated with tropical cyclones. The life of an MCS is divided into three stages: growth or initiation, maturity, and decay. Stage 1 shows divergence near 500 hPa that is characterized by warm and dry anomalies, indicative of a stable layer that caps convection. Stage 2 is distinguished from the other life cycle phases in exhibiting a cooler and moister lower troposphere. The third stage exhibits convergence in the mid-troposphere and further aloft at the tropopause, indicative of anvil remnants. Results show large accumulations of lower tropospheric moisture and instability are linked to the buoyancy and vertical motion that large-scale precipitation requires. A temporal gap is observed between greatest plume buoyancy and moisture/precipitation through the MCS life cycle. Buoyancy is a maximum in stage 1, while rainfall is a maximum in stage 2, a time when buoyancy is near zero. The near-zero buoyancy is due to a cancellation between instability and dilution. During stage 3, decay is associated with the stabilization of the lower troposphere and the cessation of convection.

 Undergraduate Research: Identifying Thermodynamic Controls on Convective Onset in the Southeastern United States Summer

Abstract:

Within the Southeastern United States (SE US) summer, deep convection occurs frequently and is difficult to forecast. This study examines thermodynamic conditions supporting deep convection onset of isolated convective systems, as well as mesoscale convective systems (MCSs). Days of interest for convective onset are identified using the ground-based precipitation radar and are matched to radiosonde and ERA5 reanalysis data to study the large-scale thermodynamic environment supporting deep convective initiation in the SE US. Ground-based radar is also used to classify organized multi-cellular convection. Comparing thermodynamic environments of locally-developing isolated systems and propagating organized convective systems, organized convective systems are sustained by moister environments than those in which isolated convective systems develop. Examining variability in the moisture vertical structure, we find that moisture is higher in the lower free troposphere in environments supporting MCSs, compared with environments supporting isolated deep convection initiation. By using geostationary imagery to identify cloud top heights (CTH), the temporal evolution of the transition from shallow to deep convection is explicitly identified and analyzed for our isolated deep convective cases. Matching ERA5 thermodynamics to our CTH analysis of the shallow-to-deep transition reveals a buildup of column moisture in the many hours preceding the convective transition. Overall, low values of CAPE, elevated and sustained total column water (TCW), and the importance of a moist surrounding environment are indications that convection within the SE US is highly dependent on moisture-based variables and have traits comparable to tropical convection. Finally, preliminary results from local field experiments (Summer 2021, Charlottesville, VA) explore physical mechanisms – e.g. dry air entrainment – relating deep convection to its thermodynamic environment in a new way.

The Leadership Alliance Summer REU: The Impact of Arctic Sea Ice Decline on Midlatitude Cyclonic Storms 

 Abstract:

The global climate is beginning to change with the Arctic warming faster than any other region on Earth. As temperatures rise, climate models show Arctic sea ice could disappear completely by the end of the century. This is expected to exert significant impacts on the midlatitude weather of the northern hemisphere. Melting sea ice reveals the darker ocean surface which absorbs more radiation from the sun. This absorption leads to Arctic warming and the temperature gradient over the northern hemisphere is reduced. This pole-to-equator gradient is semi responsible for the strength of midlatitude storms (low pressure systems or cyclones), which dominate weather and climate between the tropics and the poles. Currently, it is unclear how exactly storms will respond to the loss of Arctic sea ice. Previous climate modeling analysis predicted a weakening of the midlatitude jet-stream as a result of the northern oceans’ warming as the amount of sea ice declines. Utilizing climate model simulations, we show that Arctic sea ice loss leads to the following impacts on storms. First, without any sea ice, the Arctic warms and the midlatitude jet stream decelerates, as consistent with previous work. Secondly, the model demonstrates that without any sea ice, the tracks of midlatitude cyclones shift equator-ward and storms are more intense over Eurasia and the eastern United States during the winter months. In order to continue this research, we propose a project to compare different climate models to one another and to the reanalysis data to determine their accuracy as well as looking into more of the underlying mechanisms driving the change to midlatitude cyclonic storms. This can be achieved by analyzing models similar to ECHAM6 (the one used in the preliminary analysis), which are atmospheric global climate models. By changing the different variables fed into these models, we will be able to more fully understand the impact of Arctic sea ice loss on midlatitude storms and its connection to recent trends.