Numerical Simulations of an Isolated Microburst. Part I: Dynamics and Structure

Okayama Downbursts on 27 June 1991

“…They showed that microbursts were detected on 60% to 70% of the days during which thunderstorms occurred (Proctor, 1988). The features of the average JAWS microbursts are as follows: the life cycle is 13 minutes; the maximum low-level reflectivity in the precipitation core ranges from 15 to more than 65 dBZ; and the maximum radial velocity differential is 24m/s, occurring over a distance of 3.1km at a height of 80m AGL (Hjelmfelt, 1988).…”

“…In the US, during the period from 1974 to 1985, microburst winds contributed to at least 11 civil aircraft accidents and incidents involving over 400 fatalities and 145 injuries (Proctor, 1988 These studies indicate that microbursts are common phenomena. They showed that microbursts were detected on 60% to 70% of the days during which thunderstorms occurred (Proctor, 1988).…”

“…The features of the average JAWS microbursts are as follows: the life cycle is 13 minutes; the maximum low-level reflectivity in the precipitation core ranges from 15 to more than 65 dBZ; and the maximum radial velocity differential is 24m/s, occurring over a distance of 3.1km at a height of 80m AGL (Hjelmfelt, 1988). In theeeeeee FLOWS and JAWS studies, microburst wind shears were detected with peak differential velocities of up to 50m/s, with many more weaker ones than stronger ones (Proctor, 1988).…”

Investigating the impact of atmospheric stability on thunderstorm outflow winds and turbulence

“…RANS simulations of downburst winds (Mason et al, 2009;Proctor, 1988;Mason et al, 2010a) and LES studies (Vermeire et al, 2011a;Anabor et al, 2011;Orf et al, 2012Orf et al, , 2014 both solve the Navier-Stokes equations and have been used to 15 study the dynamics of downburst winds. What separates the two methods is that RANS models estimate the entire turbulent contributions of the flow field, while LES resolves the largest turbulent eddies and parameterizes only the smaller turbulent eddies.…”

Downbursts in the Northwestern Part of Saitama Prefecture on 8 September 1994

“…Various numerical studies (e.g., Srivastava, 1987;Proctor, 1988Proctor, , 1989Knupp, 1989;Straka and Anderson, 1993) revealed that, 1) In a dry microburst environment, where a thick dry adiabatic layer exists below the cloud base, evaporation of precipitation particles is the most important forcing to drive the microburst. If the situation is such that the temperature at the cloud base is below the freezing point and snowflakes fall from the cloud base, a stronger downdraft is expected because of the slow fallspeed of snow flakes and the additional cooling during their melting; 2) In a wet microburst environment, where the cloud base is low, the mid-level is relatively dry and CAPE is large, the formation of large precipitation particles (especially in the form of hailstones) is important to generate the microburst (Srivastava, 1987;Wakimoto and Bringi, 1988;Proctor, 1989).…”