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Leslie M. Hartten and Margaret A. LeMone

Statistics regarding the fractional participation of women in meteorology/atmospheric sciences gathered by the AMS are quite similar to those based on annual National Science Foundation (NSF) surveys. The absolute numbers in the biennial AMS/UCAR survey of academic departments for the Curricula series ceased being useful by around 2005, when many departments stopped participating fully, but numbers from less-frequent direct AMS membership surveys have been increasing. Despite the limitations of the AMS data, the NSF statistics confirm conclusions from an earlier analysis of AMS data. Both numbers and percentages are required to tell the evolving story of the atmospheric sciences' “pipeline.” Furthermore, after correction of an error regarding the AMS statistics in our 2010 paper, both NSF and AMS data show the same increase in the proportion of women graduate students in the field over the last four decades, as well as an apparent leveling off at approximately one-third.

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Sharon A. Lewis, Margaret A. LeMone, and David P. Jorgensen

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Airborne Doppler and flight-level data are used to document the structure and evolution of portions of a late-stage horseshoe-shaped squall line system and its effect on vertical momentum and mass transports. This system, which occurred on 20 February 1993 during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment, was similar to many previously studied, but had some unique features. First, a slow-moving transverse band, which formed the southern leg of the horseshoe, drew most of its low-level updraft air from the squall-line stratiform region on its north side rather than the “environment” to the south. Second, a long-lived cell with many properties similar to a midlatitude supercell, formed 150 km to the rear of the squall line. This cell was tracked for 4 h, as it propagated into and then through the cold pool, and finally dissipated as it encountered the convection forming the northern edge of the horseshoe. Finally, as the squall line was dissipating, a new convective band formed well to its rear.

The transverse band and the long-lived cell are discussed in this paper. Quadruple-Doppler radar data, made possible by tightly coordinated flights by the two NOAA P3s, are used to document the flow with unprecedented accuracy. At lower levels, the transverse band flow structure is that of a two-dimensional convective band feeding on its north side, with vertical fluxes of mass and horizontal momentum a good match to the predictions of the Moncrieff archetype model. At upper levels, the transverse band flow is strongly influenced by the squall line, whose westward-tilting updraft leads to much larger vertical velocities than predicted by the model. The long-lived cell, though weak, has supercell-like properties in addition to its longevity, including an updraft rotating in the sense expected from the environmental hodograph and an origin in an environment whose Richardson number falls within the Weisman–Klemp “supercell” regime.

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Edward J. Zipser, Rebecca J. Meitín, and Margaret A. LeMone

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The structure of the convective band of 14 September in the dense GATE observing array is determined using wind and thermodynamic data primarily from multiple aircraft penetrations, which are well distributed in the vertical and in time.

The well-defined mesoscale features in the line, which are 10–40 km in scale, quasi-two-dimensional, and persist for several hours, determine the distribution of the convective-scale features, which are 5 km or less in size, three-dimensional, not generally detectable for more than one flight leg. At the leading edge, a 30 km zone of strong ascent is computed from two-dimensional continuity. Here, lifting of the ambient air creates a favorable environment—not found elsewhere—for deep cumulonimbus clouds to develop. Their updrafts are weak, 2–4 m s−1 on the average. Behind the updraft zone, below 3–4 km, is a broad descent zone. It corresponds to the stratiform rain area, and has little convection, and some drying at lower levels. On the average, the mass flux by the mesoscale and convective-scale drafts of the updraft zone is about twice as much as that of the descent zone. The rainfall rate in the updraft zone is generally in excess of 8 mm h−1, while that in the downdraft region is less. The horizontal winds normal to the line are strongly modified by pressure forces, while those parallel to the line are changed mainly through mixing. Strong vertical vorticity is created in the line by tilting of the mean shear of the parallel component.

As the system matures, the downdraft mass flux increases relative to the updraft mass flux, so that the net mass flux becomes negative during the decay phase. The fraction of the total rain falling in the stratiform zone increases with time. However, considerable rain still falls from intense convective cells as well as the stratiform “anvil” even when the net mass flux goes to zero in the lowest kilometer.

The structure and evolution of the line is similar to that of tropical squall lines, but it is less spectacular. Winds are weaker, there is less mass flow through the system, movement is slower, and there is less drying in the rain area. The line is aligned with the wind and shear, rather than across it, as is the case for many squall lines.

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Stanley B. Trier, Margaret A. LeMone, and William C. Skamarock

Abstract

Past studies of the effects of mesoscale convective systems (MCSs) on the environmental flow have been limited by data coverage and resolution. In the current study the MCS-scale (stormwide) horizontal accelerations and momentum budget associated with an oceanic MCS are analyzed using output from a high-resolution three-dimensional numerical model integrated over a large domain. The simulation is based on an observed MCS that occurred on 22 February 1993 during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment. An important aspect of both the observed and simulated MCS is its evolution from a quasi-two-dimensional to an asymmetric three-dimensional morphology, which was demonstrated in companion studies to result from the finite length of the MCS interacting with environmental vertical shear that varies in direction with height. Herein, the authors focus on the effects of the three-dimensional structure on MCS-scale horizontal accelerations.

The horizontal accelerations over the central portion of the MCS, where its leading edge is perpendicular to the low-level environmental vertical shear, resemble those from available observations and two-dimensional models of linear squall-type MCSs. However, the vertical structure of horizontal accelerations is quite different on the MCS scale. Zonal accelerations, which are aligned along the environmental low-level vertical shear, generally exceed meridional accelerations in the lower and upper troposphere, and are dominated by the vertical flux convergence term at low levels, and by the horizontal flux convergence term at upper levels. In contrast, zonal accelerations are weaker than meridional accelerations at midlevels, owing to strong cancellation of zonal accelerations in the central portion with those along the northern periphery of the MCS, where both the alignment of the convective band relative to the environmental vertical shear and its mesoscale organization are different. This compensation between different regions of the MCS results in modifications to the environmental vertical shear by mesoscale convection that differ substantially from those typically reported in idealized studies of two-dimensional squall lines. Since three-dimensional organization often occurs in MCSs that lack persistent external linear forcing, the current findings may have implications for the parameterization of the momentum effects of mesoscale deep convection in large-scale models.

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Chin-Hoh Moeng, Gregory S. Poulos, and Margaret A. LeMone
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Margaret A. Lemone, Tae Y. Chang, and Christopher Lucas

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No abstract available.

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Margaret A. Lemone, Lesley F. Tarleton, and Gary M. Barnes

Abstract

We examine the pressure fields wound the cloud-base updraft of three cumulus clouds observed in environments with low vertical shear of the horizontal wind near cloud base. These fields are compared to the corresponding pressure fields beneath convective clouds embedded in moderate to large shear. All of the pressure fields are derived from aircraft measurements taken during the 1981 Cooperative Convective Experiment, CCOPE.

The pressure fields associated with these low-shear clouds are weaker than those for the clouds in higher shear. Furthermore, the low-shear fields are not consistently dominated by the dynamic pressure created by the interaction of the cloud-base updraft with the vertical shear of the horizontal wind. The weaker dynamic pressure is due to the smaller size and intensity of the cloud-base updraft as well as the smaller vertical shear of the horizontal wind. The reduction of the dynamic Pressure allows buoyancy effects on the pressure field to become more apparent.

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Christopher Lucas, Edward J. Zipser, and Margaret A. LeMone

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Richard C. Igau, Margaret A. LeMone, and Dingying Wei

Abstract

An examination of the properties of updraft and downdraft cores using Electra data from TOGA COARE shows that they have diameters and vertical velocities similar to cores observed over other parts of the tropical and subtropical oceans. As in previous studies, a core is defined as having vertical velocity of the same sign and greater than an absolute value of 1 m s−1 for at least 500 m. A requirement that the core contain either cloud or precipitation throughout is added, but this should not affect the results significantly.

Since the Electra was equipped with the Ophir III radiometric temperature sensor, it was also possible to make estimates of core buoyancies. As in TAMEX and EMEX, where core temperatures were estimated using the modified side-looking Barnes radiometer on the NOAA P3s, a significant fraction of both updraft and downdraft cores had apparent virtual temperatures greater than their environments. In fact, the average virtual temperature deviation from the environment for downdraft cores was +0.4 K.

Sixteen of the strongest downdraft cores were examined, all of which had positive virtual-temperature deviations, to find the source of this surprising result. It is concluded that the downdraft cores are artificially warm because 100% relative humidity was assumed in calculating virtual temperature. However, reducing core mixing ratios to more physically realistic values does not eliminate warm virtual potential temperature downdraft cores, nor does water loading make all cores negatively buoyant. Thus positively buoyant convective downdrafts do exist, though probably in smaller numbers than previously suggested.

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Christopher Lucas, Edward J. Zipser, and Margaret A. Lemone

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No abstract available

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