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E. M. Agee, J. T. Snow, F. S. Nickerson, P. R. Clare, C. R. Church, and L. A. Schaal

the multiple-vortex region may be associated with a strong vorticity feeder band similarto that reported by Golden and Purcell (1975). Several such feeder bands may concentrate the vorticityinto the core of the tornado cyclone. The tail-cloud phenomenon appears to be related to this flow featurein the tornado cyclone wind field. Radar data from Marseilles, II1., and Grissom Air Force Base, Ind., were analyzed for a portion of thelifetime of the parent thunderstorm system to determine the

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Nicole P. M. van Lipzig, Erik van Meijgaard, and Johannes Oerlemans

-Range Weather Forecasts (ECMWF) analyses have been performed with various objectives. Hines et al. (1995) employed a cloud-free version of the National Center for Atmospheric Research Mesoscale Model version 4. They found that the model is able to simulate realistic synoptic phenomena although the lack of latent heating results in some biases. The results of a comparison with automatic weather station data suggest that the model has a typical cold bias of about 2°C for June 1988. The addition of moist

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Robert M. Banta

latter conclusion. The conclusion implies that, on days with strong ridl~tol~level winds, the leeside convergence zone mechanism proposed in the earlier observational study will not be aseffective in initiating and sustaining deep convective clouds in the mountains. An evaluation of the terms in the horizontal equation of motion showed that the initial push starting theupslope winds along the lee slope in all of the runs came from the pressure-gradient force, as eipected, and aperiod of steady

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Xin Zhou and Bart Geerts

the cloud base is above Mt. Bigelow. This is the case on all days in the DSP ( Figs. 5a,c ), at least during part of the day, but not on many WSP days. On these days the CBL top does not exceed the elevation of Mt. Bigelow and/or the cloud base is below Mt. Bigelow. Thus, we can estimate the peak solenoidal forcing (i.e., the isobaric temperature difference at Mt. Bigelow pressure level, between mountain and adjacent valley) to be about 1.0 K during the DSP ( Table 1 ). Since this estimate is not

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William H. Raymond

cumulus clouds. Mon. Wea. Rev., 113, 1920-1932.Daley, R., 1991: Atmospheric Data Analysis. Cambridge University Press, 457 pp.Delden, A. van, 1989: On the deepening and filling of balanced cy clones by diabatic heating. Meteor. Almos. Phys., 41, 127-145.Donner, L. J., 1988: An initialization for cumulus convection in numerical weather prediction models. Mon. Wea. Rev., 116, 377-385.--, H. L. Kuo, and E. J. Pitcher, 1982: The significance of ther modynamic forcing by cumulus convection in a

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Nolan T. Atkins, Roger M. Wakimoto, and Conrad L. Ziegler

-resolution observations, the finescale structure in the along-line direction has not been well documented in the literature. In particular, the authors are unaware of any observational study showing a high-resolution three-dimensional wind field along the dryline that may help explain why clouds form at periodic locations. It should be noted that the dryline variability shown by Bluestein et al. (1988) , Bluestein and Parker (1993) , and Ziegler et al. (1997) is much smaller in scale than other well

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John R. Mecikalski and Gregory J. Tripoli

1. Introduction Periodic high-altitude poleward surges of cirrus laden outflow emanating from the intertropical convergence zone (ITCZ) have been referred to as “tropical plumes” by a number of investigators ( Anderson and Oliver 1970 ; Thepenier and Cruette 1981 ; McGuirk et al. 1987 ; Iskenderian 1993 , 1995 ). Some of these studies have postulated that quasigeostrophic forcing associated with large-scale Rossby waves trigger the eruption of these cloud plumes ( McGuirk et

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Robert W. Burpee

-generatedcirrus cloud cover produced by the deep convection that forms in the sea-breeze convergence zones.Before the typical midafternoon maximum of deep convection on sea-breeze days, there is no significantdifference between the surface convergence averaged for days with widespread rain and for days with littlerain. Important differences are observed, however, in the middle troposphere, where the sea-breezedays with widespread rain are more moist and have cooler temperatures than the days with little orno rain

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Marcus van Lier-Walqui, Tomislava Vukicevic, and Derek J. Posselt

1. Introduction Accurate prediction of precipitation is one of the greatest challenges of numerical weather prediction (NWP). The physical processes controlling precipitation occur at a microscopic scale and thus cannot be explicitly represented at the model resolution. The parameterization of cloud and precipitation microphysics is required, which estimates the contribution of the subgrid-scale processes on the model grid. The cloud and precipitation microphysical parameterizations include a

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C-H. Sui and K-M. Lau

atnorthern Australian region (140-E) in late December. The passage of ISOs in the monsoon flow are alsoassociated with surface westerly wind outbreaks. On shorter time scales (<10 days), the ISOs appear to providea favorable condition over the warm ocean for the development of 2-4-day disturbances that further organizemesoscale cloud dusters. In addition, the diurnal cycle provides another important forcing mechanism modulatingcloud clusters, particularly over the maritime continents. There appears to

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