Max Grover and Matthew Woods
Max Grover: Estimating Midlevel Updraft Characteristics and Severe Weather Intensity through the Lens of Overshooting Tops
Abstract:
Cloud resolving model simulations show that the horizontal area of “convective overshoots” at the top of deep convective storms relates strongly to the area of the associated updraft core within the middle troposphere. Observational support of such overshooting top area (OTA) – updraft relationships were found using coincident observations of overshooting tops (OTs) and updrafts collected in three cases during the RELAMPAGO field campaign in Córdoba province, Argentina. The RELAMPAGO data revealed different convective morphologies had different OT characteristics, with long-lived, large OTs found in association with a supercell case, smaller, shorter-lived OTs found with a multicell case, and finally, short-lived, large OTs found with an MCS case. In general, the convective storms with wide, deep, and intense updrafts tended to be associated with large and deep OTs. The results were used to explore the hypothesis that characteristics of satellite-identified OTs can be used to quantify midtropsopheric updraft area as well as intensity and vertical mass flux. Using radar-retrieved updraft area and corresponding calculations, a scaling factor and simple approach was used to estimate distributions of updraft core radii using OTs during the three cases. The estimated updraft core widths were within 1-2 km of previous measurements of updraft width in midlatitude regions.
This connection between midlevel updraft area and OTA was also used to estimate the intensity of severe convective weather phenomena, expanding upon a previous study that was focused solely on tornado intensity. Reports of severe hail, severe straight-line winds, and tornadoes were paired with their respective OT events, and then the peak intensity of severe weather and peak OTA were determined. It was shown that OTA, as well as OT depth, have some skill in distinguishing significant from nonsignificant hail size, wind intensity, and tornado intensity. OTA distributions from both a supercell and MCS were used as a case study to evaluate the ability to infer updraft characteristics from OTs.
Matthew Woods: Understanding extreme tornado events under future climate change through the pseudo-global warming methodology
Abstract:
This study aspires to determine how modern extreme tornado events may unfold under future anthropogenic climate change using the “pseudo global warming” (PGW) methodology. To properly apply this methodology, current-day extreme tornado events must be adequately simulated, and then simulated again with climate-change differences applied to the original 3D meteorological forcing. Given its classic supercellular nature and great societal impact, the 20 May 2013 EF-5 tornado that occurred in Moore, Oklahoma was chosen to be modeled. North American Mesoscale Forecast Model (NAM) data were ingested into WRF-ARW 4.0 to produce a simulation across the parent domain of the southern Great Plains and a nested domain over central Oklahoma. The domains had horizontal grid spacings of 3 and 1 km, respectively. After establishing an adequate control, climate-change deltas were added to the control input to simulate the event in a future climate. These climate change deltas are the differences in future and historical general circulation model (GCM) output from CMIP5 (Coupled Model Intercomparison Project Phase 5). Several delta construction methods were employed to provide a larger ensemble and assess the importance of delta configuration. To complement the WRF experiments, idealized simulations in Cloud Model 1 (CM1) were run for the 20 May 2013 event, as well as the 10 February 2013 event that produced an EF-4 tornado in Hattiesburg, Mississippi. This cool-season event was chosen to provide contrast to the 20 May 2013 tornado, and to determine if the influence of climate change on extreme tornado events exhibits any seasonality. Findings from 20 May WRF simulations suggest that the convective storms under PGW are stronger but tend to grow upscale more rapidly due to stronger downdrafts and cold pools. While baseline tornado proxy decreased in PGW simulations, instances of high-end tornado proxy increased. Delta configuration also had some influence on the convective response, especially at the upper thresholds of the parameters assessed. In the idealized simulations, a preliminary assessment of “tornado power” suggests higher power in the tornado-like vortices under PGW.
