James H. Ruppert, Jr., Ph.D.
Email: ruppert"at"atmos.colostate.edu
Department of Atmospheric Science, ATS 314
Colorado State University
Fort Collins, CO

Department of
Atmospheric Science
CV       Research Group       Swell Watch       SPC       NWS
Diego Garcia during DYNAMO (Oct 2011).

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Schematic diagram from Ruppert and Johnson (2014, JAS) depicting the relationship between (a) slowly evolving large-scale motion and humidity (shading), and (b) the diurnal cycle of clouds and moistening based on DYNAMO observations. The diurnal cycle of clouds (b; upper panel) during the build-up (pre-onset) stage of the MJO is driven by the large diurnal cycle in sea surface temperature and the resulting cycle in surface fluxes (b; lower panel). Convective clouds in the pre-onset stage exhibit a remarkable degree of mesoscale organization, as depicted by MODIS imagery (c).
Surface analysis from Ruppert and Bosart (2014, MWR) depicting a remarkably high-amplitude mesoscale gravity wave (MGW; red dashed line) that caused a rapid pressure drop up to ~11 hPa, wind gusts over 20 m/s, and a sudden end to rainfall at many stations as propagated northeastward through the Southeast US [analysis generated using time-to-space conversion of five-minute surface observations (pressure in black, temperature in blue), with filtered cloud-to-ground lightning strikes indicated by red dots]. The primary finding of the study is the apparent importance of the mesoscale rainfall system in sustaining the MGW's high amplitude.
Schematic from Ruppert et al. (2013, MWR) depicting the diurnal cycle of low-level circulation and rainfall during a disturbed and undisturbed period of the Mei-yu (rainy) season in Taiwan. The undisturbed period is characterized by southwesterly flow, and the disturbed period is characterized by a "Mei-yu front" that separates southwesterly flow to the south from northeasterly flow to the north and enhances lifting around Taiwan. During morning hours in both periods, the flow is deflected around Taiwan and rainfall is focused offshore. A morning lee vortex appears southwest of Taiwan in the stable northeasterly flow during the disturbed period. During afternoon hours, the flow traverses the high terrain, and thunderstorms form over Taiwan's windward slopes. Stronger impinging flow during the disturbed period leads to more vigorous thunderstorms, greater production of lofted ice, and a shift of the heaviest rainfall into the high terrain. The location of rainfall relative to the steep terrain is an important forecast problem, as where the rain falls determines the threat of floods and landslides.
The top of Rose Garden Hill on day 3 of 4 of the
Kokopelli Trail (photo credit: David Duncan).
Updated May 2015