Search for: All records

Abstract On 10 November 2018, during the RELAMPAGO field campaign in Argentina, South America, a thunderstorm with supercell characteristics was observed by an array of mobile observing instruments, including three Doppler on Wheels radars. In contrast to the archetypal supercell described in the Glossary of Meteorology, the updraft rotation in this storm was rather short lived (~25 min), causing some initial doubt as to whether this indeed was a supercell. However, retrieved 3D winds from dual-Doppler radar scans were used to document a high spatial correspondence between midlevel vertical velocity and vertical vorticity in this storm, thus providing evidence to support the supercell categorization. Additional data collected within the RELAMPAGO domain revealed other storms with this behavior, which appears to be attributable in part to effects of the local terrain. Specifically, the IOP4 supercell and other short-duration supercell cases presented had storm motions that were nearly perpendicular to the long axis of the Sierras de Córdoba Mountains; a long-duration supercell case, on the other hand, had a storm motion nearly parallel to these mountains. Sounding observations as well as model simulations indicate that a mountain-perpendicular storm motion results in a relatively short storm residence time within the narrow zone of terrain-enhanced vertical wind shear. Such a motion and short residence time would limit the upward tilting, by the left-moving supercell updraft, of the storm-relative, antistreamwise horizontal vorticity associated with anabatic flow near complex terrain. 

The pseudo‐global‐warming (PGW) methodology provides an efficient means to investigate the response of a weather or climate event under an imposed climate change signal. In the traditional PGW implementation, this signal is represented through climate‐change “deltas” constructed using monthly averages of global climate model (GCM) output over decadal or longer periods during the past and future. The implications of alternative formulations of such deltas were explored herein. Diurnally varying (DV) deltas were compared to the time‐constant (TC) deltas used in the traditional PGW implementation; this was done to test the potential effect of future changes in the diurnal cycles of temperature, humidity, and winds. Deltas created using 10‐year averages were compared to those using 30‐year averages, to examine the effects of the time‐averaging period in the delta construction. Finally, the common practice of additionally averaging across multiple GCMs to form a composite delta was also considered. Using simulations of three different historical convective storm events, it was shown that each of these PGW delta formulations results in differences in simulation metrics such as total accumulated rainfall, and convective intensity, but major and/or unambiguous differences were not always found. It is recommended that users of the PGW approach carefully consider all implications of delta formulation on their particular problem.

 

Abstract This article provides an overview of the experimental design, execution, education and public outreach, data collection, and initial scientific results from the Remote sensing of Electrification, Lightning, And Mesoscale/microscale Processes with Adaptive Ground Observations (RELAMPAGO) field campaign. RELAMPAGO was a major field campaign conducted in Córdoba and Mendoza provinces in Argentina, and western Rio Grande do Sul State in Brazil in 2018-2019 that involved more than 200 scientists and students from the US, Argentina, and Brazil. This campaign was motivated by the physical processes and societal impacts of deep convection that frequently initiates in this region, often along the complex terrain of the Sierras de Córdoba and Andes, and often grows rapidly upscale into dangerous storms that impact society. Observed storms during the experiment produced copious hail, intense flash flooding, extreme lightning flash rates and other unusual lightning phenomena, but few tornadoes. The 5 distinct scientific foci of RELAMPAGO: convection initiation, severe weather, upscale growth, hydrometeorology, and lightning and electrification are described, as are the deployment strategies to observe physical processes relevant to these foci. The campaign’s international cooperation, forecasting efforts, and mission planning strategies enabled a successful data collection effort. In addition, the legacy of RELAMPAGO in South America, including extensive multi-national education, public outreach, and social media data-gathering associated with the campaign, is summarized.