Environmental controls on simulated deep moist convection initiation occurring during RELAMPAGO-CACTI

Journal Article · 30 March 2022 · Journal of the Atmospheric Sciences

DOI: https://doi.org/10.1175/jas-d-21-0226.1 · OSTI ID:1875754

Nelson, T. Connor ^[1]; Marquis, James ^[2]; Peters, John M. ^[3]; Friedrich, Katja ^[4]

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1. Cooperative Institute for Research in the Atmosphere and NOAA/NWS Operations Proving Ground, Kansas City, MO (United States); Univ. of Colorado, Boulder, CO (United States)
2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Univ. of Colorado, Boulder, CO (United States)
3. Naval Postgraduate School, Monterey, CA (United States)
4. Univ. of Colorado, Boulder, CO (United States)

This study synthesizes the results of 13 high-resolution simulations of deep convective updrafts forming over idealized terrain using environments observed during the RELAMPAGO and CACTI field projects. Using composite soundings from multiple observed cases, and variations upon them, we explore the sensitivity of updraft properties (e.g., size, buoyancy, and vertical pressure gradient forces) to influences of environmental relative humidity, wind shear, and mesoscale orographic forcing that support or suppress deep convection initiation (CI). Emphasis is placed on differentiating physical processes affecting the development of updrafts (e.g., entrainment-driven dilution of updrafts) in environments typifying observed successful and null (i.e., no CI despite affirmative operational forecasts) CI events. Thermally-induced mesoscale orographic lift favors the production of deep updrafts originating from ~1–2-km-wide boundary layer thermals. Simulations without terrain forcing required much larger ( ~5-km-wide) thermals to yield precipitating convection. CI outcome was quite sensitive to environmental relative humidity; updrafts with increased buoyancy, depth, and intensity thrived in otherwise inhospitable environments by simply increasing the free tropospheric relative humidity. This implicates the entrainment of free-tropospheric air into updrafts as a prominent governor of CI, consistent with previous studies. Sensitivity of CI to the environmental wind is manifested by: 1) low-level flow affecting the strength and depth of mesoscale convergence along the terrain, and 2) clouds encountering updraft-suppressing pressure gradient forces while interacting with vertical wind shear in the free-troposphere. Among the ensemble of thermals occurring in each simulation, the widest deep updrafts in each simulation were the most sensitive to environmental influences.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER); National Science Foundation (NSF)
• Grant/Contract Number: AC05-76RL01830
• OSTI ID: 1875754
• Report Number(s): PNNL-SA-164690
• Journal Information: Journal of the Atmospheric Sciences, Journal Name: Journal of the Atmospheric Sciences Journal Issue: 7 Vol. 79; ISSN 0022-4928
• Publisher: American Meteorological SocietyCopyright Statement
• Country of Publication: United States
• Language: English