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Robert Rogers

processes occurring within the vortex during RI. Malkus and Riehl (1960) , Simpson et al. (1998) , and Braun (2002 , 2006) identified deep, undilute convective cores in the eyewall, which they termed hot towers, as accomplishing a significant portion of the vertical mass flux in the eyewall. These hot towers, termed convective bursts in the current parlance, are driven by local buoyancy, where “local” is meant to refer to their buoyancy relative to the immediate environment of the eyewall ( Smith

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Andrew J. Heymsfield, Aaron Bansemer, Gerald Heymsfield, and Alexandre O. Fierro

Abstract

Anvils produced by vigorous tropical convection contribute significantly to the earth’s radiation balance, and their radiative properties depend largely on the concentrations and sizes of the ice particles that form them. These microphysical properties are determined to an important extent by the fate of supercooled droplets, with diameters from 3 to about 20 microns, lofted in the updrafts. The present study addresses the question of whether most or all of these droplets are captured by ice particles or if they remain uncollected until arriving at the −38°C level where they freeze by homogeneous nucleation, producing high concentrations of very small ice particles that can persist and dominate the albedo.

Aircraft data of ice particle and water droplet size distributions from seven field campaigns at latitudes from 25°N to 11°S are combined with a numerical model in order to examine the conditions under which significant numbers of supercooled water droplets can be lofted to the homogeneous nucleation level. Microphysical data were collected in pristine to heavily dust-laden maritime environments, isolated convective updrafts, and tropical cyclone updrafts with peak velocities reaching 25 m s−1. The cumulative horizontal distance of in-cloud sampling at temperatures of −20°C and below exceeds 50 000 km. Analysis reveals that most of the condensate in these convective updrafts is removed before reaching the −20°C level, and the total condensate continues to diminish linearly upward. The amount of condensate in small (<50 μm in diameter) droplets and ice particles, however, increases upward, suggesting new droplet activation with an appreciable radiative impact. Conditions promoting the generation of large numbers of small ice particles through homogeneous ice nucleation include high concentrations of cloud condensation nuclei (sometimes from dust), removal of most of the water substance between cloud base and the −38°C levels, and acceleration of the updrafts at mid- and upper levels such that velocities exceed 5–7 m s−1.

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Chanh Q. Kieu and Da-Lin Zhang

intensity. The objectives of the present study are (i) to examine the kinematics of the vortex merger in relation to convectively generated vortices (CGVs) in the ITCZ and the associated multiscale interactive processes; (ii) to quantify the roles of merging MCVs, surface heat fluxes, and PV sources in the ITCZ in the formation of TS Eugene (2005); and (iii) to determine whether or not TCG from merging MCVs would occur from the bottom upward or the top downward. These objectives will be achieved by

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Chanh Q. Kieu and Da-Lin Zhang

barotropic framework (e.g., Holland and Dietachmayer 1993 ; Prieto et al. 2003 ; Kuo et al. 2008 ), the merging process in the present case is characterized by sharp increases in the surface heat fluxes, the low-level convergence, latent heat release (and upward motion), the low to midtropospheric potential vorticity (PV), surface pressure fall, and the rapid growth of cyclonic vorticity in the lower troposphere. Our PV budget calculations in Part II show two different episodes of the storm

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Wallace Hogsett and Da-Lin Zhang

1. Introduction Tropical cyclones (TCs) devastate life and property by concentrating large amounts of kinetic energy (KE) within a small radius in the inner-core regions. Most of the KE is generated through a continuous series of energy conversions, with the latent energy (LE) as the fundamental source, which is obtained primarily through upward fluxes of latent heat from the underlying warm ocean and released in convective clouds in the eyewall. Some of the released LE is used to increase KE

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Jonathan L. Vigh and Wayne H. Schubert

normalization, the ψ ( r , z ) and T t ( r , z ) fields can be written as Figure 1 shows contours of rψ and T t in the ( r , z ) plane for this resting atmosphere case. These plots have been constructed from (4.5) and (4.6) using the Green’s function Eqs. (4.1) and (4.2) . Note that rψ is negative for r < 25 km and positive for r > 25 km, which means that the transverse mass flux is counterclockwise for r < 25 km and clockwise for r > 25 km. The discontinuity of rψ at r = 25

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R. A. Hansell, S. C. Tsay, Q. Ji, N. C. Hsu, M. J. Jeong, S. H. Wang, J. S. Reid, K. N. Liou, and S. C. Ou

the field. In addition, the limited experimental data on dust optical properties at infrared wavelengths and the large uncertainties in the spatially and temporally dependent particle properties—size, shape, and composition ( Sokolik and Toon 1999 )—have indeed made it a difficult challenge to constrain the LW impact. The term “aerosol radiative forcing” is now commonly used for gauging changes in the radiative fluxes due to anthropogenic aerosols since the beginning of the industrial era (∼1750

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Zhuo Wang, M. T. Montgomery, and T. J. Dunkerton

tests were also carried out with different model physics or initial conditions, which are described in detail in Part II . b. Flux form of the vorticity budget Following Haynes and McIntyre (1987) , Tory and Montgomery (2008) , and Raymond et al. (1998) , the flux form of the vorticity equation in the isobaric coordinates can be written as where the absolute vorticity is defined as ω is pressure vertical velocity, and according to DMW09 the wave relative flow is where i is the unit vector

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Joël Arnault and Frank Roux

following prognostic equation for ρ m : In (19) , the tendency of ρ m is equal to the sum of its flux divergence plus a term quantifying the variation of mass of moist air due to changes in the water vapor content. Introducing (19) in the momentum equation of Bannon (2002) , we obtain In (20) , (21) , and (22) , the terms related to the earth’s curvature have been neglected; (a1), (b1), (c1) and (a2), (b2), and (c2) are the tendencies and flux divergences of moist momentum, respectively; (a3

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Gerald M. Heymsfield, Lin Tian, Andrew J. Heymsfield, Lihua Li, and Stephen Guimond

heights and vertical velocity as well as the relationship between peak updraft speeds and reflectivity contour levels. These observational details are important because they have implications for understanding convective dynamics including mass fluxes and latent heating. The statistics presented in section 3 will be compared with previous satellite-based and aircraft-based convection measurements (e.g., Black et al. 1996 ). Another important aspect of the observations shown in this paper is the

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