Anticyclonic Rossby wave breaking (RWB) is characterized by the rapid and irreversible deformation of potential vorticity (PV) contours on isentropic surfaces manifesting as a pair of meridionally elongated high- and low-PV tongues that transport extratropical stratospheric air equatorward and tropical tropospheric air poleward, respectively. RWB occurs most commonly during the summer months and has been shown to have far-reaching impacts on tropical convection and tropical cyclone genesis. Given these important implications and the lack of literature surrounding summertime RWB, I was motivated to uncover what drove the frequency, genesis, and variability of these phenomena through both observational and modeling studies.
Results from the observational study exhibited a potentially meaningful correlation between the intrabasin distribution of anticyclonic RWB events and the June–September-averaged Pacific decadal oscillation (PDO) index, such that when the PDO is positive, there is a favorability for RWB events over the eastern half of the North Atlantic, while the opposite holds true when the averaged PDO index is negative. To test this hypothesized PDO-RWB relationship an idealized modeling experiment was performed, with results supporting those in the observational study. Analysis of the large-scale circulation and synoptic environment changes imposed by the sea surface temperature anomalies of each simulation reveals different pathways for precursor Rossby wave train (RWT) development that, in turn, affect North Atlantic RWB statistics. When the PDO signals are divided into different components, the largest changes in RWB statistics are shown to occur whenever positive sea surface temperature anomalies are present in the North Pacific, as these serve as fuel for higher frequency RWT development and therefore more dramatic changes to North Atlantic RWB statistics.
Atmospheric rivers (ARs) are narrow filaments of high water vapor content that extend thousands of kilometers, carry more water than 27 Mississippi Rivers combined on average, and play integral roles in the global water cycle. In my research I aim to perform a large-scale analysis of the dynamic and thermodynamic properties of landfalling ARs over western Europe. A climatology of landfalling ARs is established from 1980 to 2017, in which 578 ARs are identified. Examination of the upper-level PV fields shows that 73% of these AR events are related to anticyclonic RWB, a dynamic feature which has been shown to play a role in AR strength and structure. AR variability is also found to be closely tied to jet-stream latitude modulation by the North Atlantic Oscillation (NAO), such that during a positive NAO the North Atlantic jet is shifted north, creating an environment that is more favorable for anticyclonic RWB and AR landfalls over northern Europe, and during a negative NAO it is shifted south, creating such an environment over southern Europe. Through the use of linear regression analysis, AR strength is shown to be dependent on atmospheric moisture availability, which is found to increase as sea surface temperatures increase. Therefore, in a warming climate warmer sea surface temperatures leading to higher atmospheric moisture availability will result in an increase in the average strength and intensity of ARs over western Europe—a trend that has already been observed.
This project is still in its early stages, check back later for updates/results!