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The field campaign, involving multiple aircraft and ground-based instruments, documented numerous long-lived mesoscale convective systems, many producing strong surface winds and exhibiting mesoscale rotation.

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Abstract. The observed July 10, 1996, Stratospheric-Tropospheric Experiment: Radiation, Aerosols, and Ozone (STERAO)convective system is broadly reproduced in a nonhydrostatic cloud model simulation using an idealized horizontally homogeneous sounding and no terrain. System evolution from a multicellular line to a supercell, along with line orientation, anvil structure, horizontal wind fields, depth of convection, and derived radar reflectivity, compares well with observations. Simulated passive tracer transport of CO and ozone generally agrees with aircraft measurements and shows a small amount of entrainment of environmental air in the updrafts, and a small amount of dilution occurring with transport downwind in the anvil; the entrainment and dilution are less pronounced in the supercell stage. The horizontally integrated vertical flux divergence for CO in the simulation shows a net gain at almost all levels above 8 km mean sea level (msl). The rate of increase of CO mass above 8 km varies significantly in time, with a peak at early times, followed by a decline and minimum as the system transitions to a supercell and a steady increase as the supercell matures. Trajectory analyses show that updrafts in the simulation are ingesting air from a layer spanning from 2 km to 3.5 km msl (from 0.5 to 2 km above the surface). The residence times for parcels in the updraft varies from just under 10 min to more than 20 min, with most parcels taking approximately 10 min to ascend to the anvil.

A large-amplitude mountain wave generated by strong southwesterly flow over southern Greenland was observed during the Fronts and Atlantic Storm-Track Experiment (FASTEX) on 29 January 1997 by the NOAA G-IV research aircraft. Dropwindsondes deployed every 50 km and flight level data depict a vertically propagating large-amplitude wave with deep convectively unstable layers, potential temperature perturbations of 25 K that deformed the tropopause and lower stratosphere, and a vertical velocity maximum of nearly 10 m s Ϫ1 in the stratosphere. The wave breaking was associated with a large vertical flux of horizontal momentum and dominated by quasi-isotropic turbulence. The Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS) nonhydrostatic model with four-nested grid meshes with a minimum resolution of 1.7 km accurately simulates the amplitude, location, and timing of the mountain wave and turbulent breakdown. Finescale low-velocity plumes that resemble wakelike structures emanate from highly dissipative turbulent regions of wave breaking in the lower stratosphere. Idealized adiabatic threedimensional simulations suggest that steep terrain slopes increase the effective Rossby number of the relatively wide Greenland plateau, decrease the sensitivity of the wave characteristics to rotation, and ultimately increase the tendency for wave breaking. Linear theory and idealized simulations indicate that diabatic cooling within the boundary layer above the Greenland ice sheet augments the effective mountain height and increases the wave amplitude and potential for wave breaking for relatively wide obstacles such as Greenland.

[1] A pair of simultaneous, horizontally displaced, thunderstorm electric field soundings are used to investigate an existing conceptual model of thunderstorm charge structure. The soundings show that two different vertical charge structures, one in the updraft and one outside the updraft, can exist at the same time inside a storm, as depicted in the existing model. The data suggest that the two charge structures can be relatively close together, since the soundings are separated by only 3 to 8 km horizontally in the convective region of the storm. Horizontal extent of the charge structures is estimated to be at least 4 km  4 km. The differences in the two charge structures are coincident with substantial differences over this same 3 to 8 km horizontal distance in the reflectivity structure, updraft speed, and lightning activity of the convection. The nonupdraft sounding was made through the intense reflectivity core found at middle levels in the convection. Additional electric field complexity and additional charge regions were found in the nonupdraft sounding, and the lightning-related electric field changes tended to be larger in magnitude and more numerous in that sounding than in the updraft sounding.

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