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Marcia Cronce
,
Robert M. Rauber
,
Kevin R. Knupp
,
Brian F. Jewett
,
Justin T. Walters
, and
Dustin Phillips

1. Introduction Mesoscale precipitation bands often develop in the north and northwest quadrants of extratropical cyclones ( Novak et al. 2004 ). From many studies, it appears that the vertical motions in mesoscale bands are forced by frontogenesis, either in an environment that is stable to upright convection and characterized by small moist symmetric stability (e.g., Thorpe and Emanuel 1985 ; Sanders and Bosart 1985 ; Sanders 1986 ) or in an environment characterized by weak moist

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R. D. Sharman
and
J. M. Pearson

Abstract

Current automated aviation turbulence forecast algorithms diagnose turbulence from numerical weather prediction (NWP) model output by identifying large values in computed horizontal or vertical spatial gradients of various atmospheric state variables (velocity; temperature) and thresholding these gradients empirically to indicate expected areas of “light,” “moderate,” and “severe” levels of aviation turbulence. This approach is obviously aircraft dependent and cannot accommodate the many different aircraft types that may be in the airspace. Therefore, it is proposed to provide forecasts of an atmospheric turbulence metric: the energy dissipation rate to the one-third power (EDR). A strategy is developed to statistically map automated turbulence forecast diagnostics or groups of diagnostics to EDR. The method assumes a lognormal distribution of EDR and uses climatological peak EDR data from in situ equipped aircraft in conjunction with the distribution of computed diagnostic values. These remapped values can then be combined to provide an ensemble mean EDR that is the final forecast. New mountain-wave-turbulence algorithms are presented, and the lognormal mapping is applied to them as well. The EDR forecasts are compared with aircraft in situ EDR observations and verbal pilot reports (converted to EDR) to obtain statistical performance metrics of the individual diagnostics and the ensemble mean. It is shown by one common performance metric, the area under the relative operating characteristics curve, that the ensemble mean provides better performance than forecasts from individual model diagnostics at all altitudes (low, mid-, and upper levels) and for two input NWP models.

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Gandikota V. Rao

primary importance in maintaining frontogenesis in the lowest layers.This convergence is chiefly responsible for drawing moist warm air and cold air into closer contact. Thisresulted in a solenoidally direct circulation. 2) The effect of this circulation is to cause frontolysis at higher levels. However, when the release oflatent heat is taken into account frontogenesis may result, depending upon the amount and the distributionof the heat released. 3) Meteorological quantities, such as

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W. S. Creswick

in frontolysis along the temperature discontinuity, frontogenesis in the convergent regions of thewind discontinuity, and frontogenesis due to differentialcooling along the ascending portions of the moisturediscontinuity. Differential radiation due to large cloudmasses or to the snow line may have a frontogeneficaleffect, as may turbulence. Even with well-defined fronts,continuity in the vertical is seldom perfect; a single jetstream is normally associated with two fronts, one whichdevelops in

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M. A. Shapiro
and
James J. O'Brien

vorticity equation. Tdlus, 2, 237-254.Hill, G. E., 1968: Grid telescoping in numerical weather prediction. J. A ppl. Meteor., 7, 29-38.Newton, C. W., 1954: Frontogenesis and frontolysis as a threedimensional process. J. Meteor., 11, 449-461.Reed, R. J., 1955: A study of a characteristic type of upper-level frontogenesis. J. Meteor., 12, 226-237.--, and E. F. Sanders, 1953: The investigation of the develop ment of a mid-tropospheric frontal zone and its associated vorticity field. J. Meteor

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Cheng You
and
Jimmy Chi-Hung Fung

propagation inland is obviously smaller than that of SB_on ( Fig. 15 ). Arritt (1993) proposed that the offshore background wind enhances the convergence in the vicinity of the sea-breeze front and therefore strengthens the frontogenesis there, as is verified in this research. From Fig. 15 , for SB_off is larger than that of SB_on ( Figs. 15a,d ), and it is mostly contributed by FG2 + FG3 ( Fig. 15c ). However, the stronger shear of vertical motion in SB_off induces frontolysis above the sea breeze

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Victoria A. Sinclair

diurnal cycles in surface heat fluxes, boundary layer structure, and coastal, mesoscale circulation patterns can both modulate the time that synoptic-scale fronts pass over Helsinki and modify the temperature gradient of synoptic-scale fronts near the surface via diabatic frontogenesis or frontolysis. The morning peak in warm front passages in Helsinki likely occurs as warm fronts primarily approach Helsinki from the south and southwest and hence nocturnal land breezes directed off shore can prevent

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Shyama Mohanty
,
Madhusmita Swain
,
Raghu Nadimpalli
,
K. K. Osuri
,
U. C. Mohanty
,
Pratiman Patel
, and
Dev Niyogi

gradient. The scalar function of frontogenesis function F n is represented as F n = d d t | ∇ θ | , where θ is the potential temperature ( Morgan 1999 ). The concentrated thermal and moist gradients between the air masses along a quasi-linear narrow zone produce transverse closed sea-breeze-like circulation cells. The circulation centered on frontogenesis–frontolysis (negative value) couplet occurring near Mumbai ( Fig. 10b ) with rising air aids the local, heavy precipitation along the warmer zone

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M. A. Shapiro
and
J. T. Hastings

., 1954: Frontogenesis and frontolysis as a three dimensional process. J. Meteor., 11, 449-461.----, 1959: Synoptic comparisons of jet stream and Gulf Stream systems. The Atmosphere and the Sea in..Motion (Rossby Memorial Volume), New York, Rockefeller Institute Press, 288-304.P*.o, Yih-Ho and Arnold Goldburg, 1969: Clear Air Turbulence and its Detection. New York, Plenum Press, 525 pp.Reed, R. J., and E. F. Danielsen, 1959: Fronts in the vicinity of the tropopause. Arch. Meteor. Geophys

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William E. Togstad
and
Lyle H. Horn

.Murray, R., and S. M. Daniels, 1953: Transverse flow at entrance and exit to jet streams. Quart. J. Roy. Meteor. Soc., 79, 236-241.Newton, C. W., 1954: Frontogenesis and frontolysis as a three dimensional process. J. Meteor., 11, 449-461.Palm~n, E., and C. W. Newton, 1969: Atmospheric Circulation Systems. New York, Academic Press, 603 pp.Reiter, E., 1963: Jet Stream Meteorology. The University of Chicago Press, 515 pp.Riehl, H., J. Badner, J. E. Horde, N. E. LaSeur, L. L. Means, W. C. Palmer

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