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Margaret A Lemone - One of the best experts on this subject based on the ideXlab platform.
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on how hot towers fuel the hadley cell an observational and modeling study of line organized convection in the equatorial trough from toga coare
Journal of the Atmospheric Sciences, 2009Co-Authors: Alexandre O Fierro, Joanne Simpson, Margaret A Lemone, Jerry M Straka, Bradley F SmullAbstract:Abstract An airflow trajectory analysis was carried out based on an idealized numerical simulation of the nocturnal 9 February 1993 equatorial oceanic squall line observed over the Tropical Ocean and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) ship array. This simulation employed a nonhydrostatic numerical cloud model, which features a sophisticated 12-class bulk microphysics scheme. A second convective system that developed immediately south of the ship array a few hours later under similar environmental conditions was the subject of intensive airborne quad-Doppler radar observations, allowing observed airflow trajectories to be meaningfully compared to those from the model simulation. The results serve to refine the so-called hot tower hypothesis, which postulated the notion of undiluted ascent of boundary layer air to the high troposphere, which has for the first time been tested through coordinated comparisons with both model output and detailed observations. For parcel...
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structure and evolution of the 22 february 1993 toga coare squall line aircraft observations of precipitation circulation and surface energy fluxes
Journal of the Atmospheric Sciences, 1997Co-Authors: David P Jorgensen, Margaret A Lemone, Stanley B TrierAbstract:Abstract This study documents the precipitation and kinematic structure of a mature, eastward propagating, oceanic squall line system observed by instrumented aircraft during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). Doppler radar and low-level in situ observations are used to show the evolution of the convection from an initially linear NNW–SSE-oriented convective line to a highly bow-shaped structure with an embedded low- to midlevel counterclockwise rotating vortex on its northern flank. In addition to previously documented features of squall lines such as highly upshear-tilted convection on its leading edge, a channel of strong front-to-rear flow that ascended with height over a “rear-inflow” that descended toward the convective line, and a pronounced low-level cold pool apparently fed from convective and mesoscale downdrafts from the convective line; rearward, the observations of this system showed distinct multiple maxima in updraft strength with...
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structure and evolution of the 22 february 1993 toga coare squall line organization mechanisms inferred from numerical simulation
Journal of the Atmospheric Sciences, 1997Co-Authors: Stanley B Trier, William C Skamarock, Margaret A LemoneAbstract:Abstract Mechanisms responsible for meso- and convective-scale organization within a large tropical squall line that occurred on 22 February 1993 during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment are investigated using a three-dimensional numerical cloud model. The squall line occurred in an environment typical of fast-moving tropical squall lines, characterized by moderate convective available potential energy and moderate-to-strong vertical shear beneath a low-level jet with weak reverse vertical shear above. A well-simulated aspect of the observed squall line is the evolution of a portion of its leading convective zone from a quasi-linear to a three-dimensional bow-shaped structure over a 2-h period. This transition is accompanied by the development of both a prominent mesoscale vortex along the northern edge of the 40–60-km long bow-shaped feature and elongated bands of weaker reflectivity situated rearward and oriented transverse to the leading edge, within enha...
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structure and evolution of the 22 february 1993 toga coare squall line numerical simulations
Journal of the Atmospheric Sciences, 1996Co-Authors: Stanley B Trier, William C Skamarock, Margaret A Lemone, David B Parsons, David P JorgensenAbstract:Abstract In this study a numerical cloud model is used to simulate the three-dimensional evolution of an oceanic tropical squall line observed during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment and investigate the impact of small-scale physical processes including surface fluxes and ice microphysics on its structure and evolution. The observed squall line was oriented perpendicular to a moderately strong low-level jet. Salient features that are replicated by the model include an upshear-tilted leading convective region with multiple updraft maxima during its linear stage and the development of a 30-km scale midlevel vortex and associated transition of the line to a pronounced bow-shaped structure. In this modeling approach, only surface flukes and stresses that differ from those of the undisturbed environment are included. This precludes an unrealistically large modification to the idealized quasi-steady base state and thus allows us to more easily isolate effects of ...
Stanley B Trier - One of the best experts on this subject based on the ideXlab platform.
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structure and evolution of the 22 february 1993 toga coare squall line aircraft observations of precipitation circulation and surface energy fluxes
Journal of the Atmospheric Sciences, 1997Co-Authors: David P Jorgensen, Margaret A Lemone, Stanley B TrierAbstract:Abstract This study documents the precipitation and kinematic structure of a mature, eastward propagating, oceanic squall line system observed by instrumented aircraft during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). Doppler radar and low-level in situ observations are used to show the evolution of the convection from an initially linear NNW–SSE-oriented convective line to a highly bow-shaped structure with an embedded low- to midlevel counterclockwise rotating vortex on its northern flank. In addition to previously documented features of squall lines such as highly upshear-tilted convection on its leading edge, a channel of strong front-to-rear flow that ascended with height over a “rear-inflow” that descended toward the convective line, and a pronounced low-level cold pool apparently fed from convective and mesoscale downdrafts from the convective line; rearward, the observations of this system showed distinct multiple maxima in updraft strength with...
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structure and evolution of the 22 february 1993 toga coare squall line organization mechanisms inferred from numerical simulation
Journal of the Atmospheric Sciences, 1997Co-Authors: Stanley B Trier, William C Skamarock, Margaret A LemoneAbstract:Abstract Mechanisms responsible for meso- and convective-scale organization within a large tropical squall line that occurred on 22 February 1993 during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment are investigated using a three-dimensional numerical cloud model. The squall line occurred in an environment typical of fast-moving tropical squall lines, characterized by moderate convective available potential energy and moderate-to-strong vertical shear beneath a low-level jet with weak reverse vertical shear above. A well-simulated aspect of the observed squall line is the evolution of a portion of its leading convective zone from a quasi-linear to a three-dimensional bow-shaped structure over a 2-h period. This transition is accompanied by the development of both a prominent mesoscale vortex along the northern edge of the 40–60-km long bow-shaped feature and elongated bands of weaker reflectivity situated rearward and oriented transverse to the leading edge, within enha...
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structure and evolution of the 22 february 1993 toga coare squall line numerical simulations
Journal of the Atmospheric Sciences, 1996Co-Authors: Stanley B Trier, William C Skamarock, Margaret A Lemone, David B Parsons, David P JorgensenAbstract:Abstract In this study a numerical cloud model is used to simulate the three-dimensional evolution of an oceanic tropical squall line observed during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment and investigate the impact of small-scale physical processes including surface fluxes and ice microphysics on its structure and evolution. The observed squall line was oriented perpendicular to a moderately strong low-level jet. Salient features that are replicated by the model include an upshear-tilted leading convective region with multiple updraft maxima during its linear stage and the development of a 30-km scale midlevel vortex and associated transition of the line to a pronounced bow-shaped structure. In this modeling approach, only surface flukes and stresses that differ from those of the undisturbed environment are included. This precludes an unrealistically large modification to the idealized quasi-steady base state and thus allows us to more easily isolate effects of ...
Richard H Johnson - One of the best experts on this subject based on the ideXlab platform.
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corrected toga coare sounding humidity data impact on diagnosed properties of convection and climate over the warm pool
Journal of Climate, 2003Co-Authors: Paul E Ciesielski, Richard H Johnson, Patrick T Haertel, Junhong WangAbstract:This study reports on the humidity corrections in the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean‐Atmosphere Response Experiment (COARE) upper-air sounding dataset and their impact on diagnosed properties of convection and climate over the warm pool. During COARE, sounding data were collected from 29 sites with Vaisala-manufactured systems and 13 sites with VIZ-manufactured systems. A recent publication has documented the characteristics of the humidity errors at the Vaisala sites and a procedure to correct them. This study extends that work by describing the nature of the VIZ humidity errors and their correction scheme. The corrections, which are largest in lower-tropospheric levels, generally increase the moisture in the Vaisala sondes and decrease it in the VIZ sondes. Use of the corrected humidity data gives a much different perspective on the characteristics of convection during COARE. For example, application of a simple cloud model shows that the peak in convective mass flux shifts from about 88N with the uncorrected data to just south of the equator with corrected data, which agrees better with the diagnosed vertical motion and observed rainfall. Also, with uncorrected data the difference in mean convective available potential energy (CAPE) between Vaisala and VIZ sites is over 700 J kg21; with the correction, both CAPEs are around ;1300 J kg21, which is consistent with a generally uniform warm pool SST field. These results suggest that the intensity and location of convection would differ significantly in model simulations with humidity-corrected data, and that the difficulties which the reanalysis products had in reproducing the observed rainfall during COARE may be due to the sonde humidity biases. The humidity-corrected data appear to have a beneficial impact on budget-derived estimates of rainfall and radiative heating rate, such that revised estimates show better agreement with those from independent sources.
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rainfall and radiative heating rates from toga coare atmospheric budgets
Journal of the Atmospheric Sciences, 2000Co-Authors: Richard H Johnson, Paul E CiesielskiAbstract:Abstract Atmospheric heat and moisture budgets are used to determine rainfall and radiative heating rates over the western Pacific warm pool during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). Results are compared to independent estimates of these quantities from the other sources. Using the COARE bulk flux algorithm to estimate surface evaporation over the intensive flux array (IFA), the IFA moisture budget-derived average rainfall for the 120-day intensive observing period (IOP) is 8.2 mm day−1. This value agrees closely with recent estimates from satellites and the ocean salinity budget. For a smaller area within the IFA containing the rain-mapping domain of the TOGA and Massachusetts Institute of Technology 5-cm radars, the atmospheric budget for the 101-day radar deployment yields 6.8 mm day−1, slightly greater than the independent radar rain rate estimate of 5.4 mm day−1. Comparison of budget-derived rainfall with National Centers for Environmental ...
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q 2000 American Meteorological Society Rainfall and Radiative Heating Rates from TOGA COARE Atmospheric Budgets
1998Co-Authors: Richard H Johnson, E. CiesielskiAbstract:Atmospheric heat and moisture budgets are used to determine rainfall and radiative heating rates over the western Pacific warm pool during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). Results are compared to independent estimates of these quantities from the other sources. Using the COARE bulk flux algorithm to estimate surface evaporation over the intensive flux array (IFA), the IFA moisture budget-derived average rainfall for the 120-day intensive observing period (IOP) is 8.2 mm day21. This value agrees closely with recent estimates from satellites and the ocean salinity budget. For a smaller area within the IFA containing the rain-mapping domain of the TOGA and Massachusetts Institute of Technology 5-cm radars, the atmospheric budget for the 101-day radar deployment yields 6.8 mm day21, slightly greater than the independent radar rain rate estimate of 5.4 mm day21. Comparison of budget-derived rainfall with National Centers for Environmental Prediction and European Centre for Medium-Range Weather Forecasts reanalyses indicates that the reanalyses produce excessive precip-itation in the northern ITCZ (around 108N) in association with anomalously moist low-level conditions at those latitudes. These anomalous conditions arise from moist-biased VIZ humidity sensors on rawinsondes launched at operational sites there, while outside those latitudes dry-biased Vaisala sensors were almost exclusively used
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heating moistening and rainfall over the western pacific warm pool during toga coare
Journal of the Atmospheric Sciences, 1996Co-Authors: Richard H JohnsonAbstract:Abstract Rawinsonde, surface, and satellite data collected from the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean Atmosphere Response Experiment (COARE) are used to investigate the distributions of beating, moistening, precipitation, and evaporation over the western Pacific warm pool. The behavior of the atmosphere and the response of the ocean surface before, during, and after the passages of westerly wind bursts are examined. The tropospheric vertical wind shear associated with tropical low-frequency oscillations strongly modulated convective beating and moistening. Heavy precipitation usually fell 1 to 3 weeks prior to the peak westerly wind bursts. SSTs reached their maximum during the undisturbed phase of the intraseasonal oscillations (ISOs), gradually decreased as convection intensified, and reached their minimum during the periods of peak westerly winds when deep convection was generally suppressed over the intensive flux array (IFA). Surface latent heat fluxes were positively correlated w...
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kinematic and thermodynamic characteristics of the flow over the western pacific warm pool during toga coare
Journal of the Atmospheric Sciences, 1996Co-Authors: Xin Lin, Richard H JohnsonAbstract:Abstract Rawinsonde and satellite infrared radiation (IR) data from the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean Atmosphere Response Experiment (COARE) are used to investigate mean and transient behavior and horizontal variability of the atmosphere over the western Pacific warm pool. Infrared data for the 4-mo Intensive Observing Period (IOP) and vertical motion fields indicate that the intensity of convection, height of maximum upward motion, and SST all increased from west (140°E) to east across the COARE domain. IOP-mean IR data show a double ITCZ (Intertropical Convergence Zone) structure north and south of the Intensive Flux Array (IFA, centered at 2°S, 156°E), although marked variability in the patterns occurred on a month to month basis. Three prominent westerly wind bursts occurred over the IFA during the 4-mo IOP in association with the intraseasonal oscillations (ISOs). Strong upward motion usually occurred 1–3 weeks prior to the peak low-level westerlies. Subsidence dominated when ...
David P Jorgensen - One of the best experts on this subject based on the ideXlab platform.
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structure and evolution of the 22 february 1993 toga coare squall line aircraft observations of precipitation circulation and surface energy fluxes
Journal of the Atmospheric Sciences, 1997Co-Authors: David P Jorgensen, Margaret A Lemone, Stanley B TrierAbstract:Abstract This study documents the precipitation and kinematic structure of a mature, eastward propagating, oceanic squall line system observed by instrumented aircraft during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE). Doppler radar and low-level in situ observations are used to show the evolution of the convection from an initially linear NNW–SSE-oriented convective line to a highly bow-shaped structure with an embedded low- to midlevel counterclockwise rotating vortex on its northern flank. In addition to previously documented features of squall lines such as highly upshear-tilted convection on its leading edge, a channel of strong front-to-rear flow that ascended with height over a “rear-inflow” that descended toward the convective line, and a pronounced low-level cold pool apparently fed from convective and mesoscale downdrafts from the convective line; rearward, the observations of this system showed distinct multiple maxima in updraft strength with...
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structure and evolution of the 22 february 1993 toga coare squall line numerical simulations
Journal of the Atmospheric Sciences, 1996Co-Authors: Stanley B Trier, William C Skamarock, Margaret A Lemone, David B Parsons, David P JorgensenAbstract:Abstract In this study a numerical cloud model is used to simulate the three-dimensional evolution of an oceanic tropical squall line observed during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment and investigate the impact of small-scale physical processes including surface fluxes and ice microphysics on its structure and evolution. The observed squall line was oriented perpendicular to a moderately strong low-level jet. Salient features that are replicated by the model include an upshear-tilted leading convective region with multiple updraft maxima during its linear stage and the development of a 30-km scale midlevel vortex and associated transition of the line to a pronounced bow-shaped structure. In this modeling approach, only surface flukes and stresses that differ from those of the undisturbed environment are included. This precludes an unrealistically large modification to the idealized quasi-steady base state and thus allows us to more easily isolate effects of ...
Jean-luc Redelsperger - One of the best experts on this subject based on the ideXlab platform.
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a gcss model intercomparison for a tropical squall line observed during toga coare ii intercomparison of single column models and a cloud resolving model
Quarterly Journal of the Royal Meteorological Society, 2007Co-Authors: Peter Bechtold, Jean-luc Redelsperger, I Beau, Michael Blackburn, S Brinkop, J Y Grandper, A Grant, David Gregory, Francoise Guichard, E IoannidouAbstract:This paper presents single-column model (SCM) simulations of a tropical squall-line case observed during the Coupled Ocean-Atmosphere Response Experiment of the Tropical Ocean/Global Atmosphere Programme. This case-study was part of an international model intercomparison project organized by Working Group 4 ‘Precipitating Convective Cloud Systems’ of the GEWEX (Global Energy and Water-cycle Experiment) Cloud System Study. Eight SCM groups using different deep-convection parametrizations participated in this project. The SCMs were forced by temperature and moisture tendencies that had been computed from a reference cloud-resolving model (CRM) simulation using open boundary conditions. The comparison of the SCM results with the reference CRM simulation provided insight into the ability of current convection and cloud schemes to represent organized convection. The CRM results enabled a detailed evaluation of the SCMs in terms of the thermodynamic structure and the convective mass flux of the system, the latter being closely related to the surface convective precipitation. It is shown that the SCMs could reproduce reasonably well the time evolution of the surface convective and stratiform precipitation, the convective mass flux, and the thermodynamic structure of the squall-line system. The thermodynamic structure simulated by the SCMs depended on how the models partitioned the precipitation between convective and stratiform. However, structural differences persisted in the thermodynamic profiles simulated by the SCMs and the CRM. These differences could be attributed to the fact that the total mass flux used to compute the SCM forcing differed from the convective mass flux. The SCMs could not adequately represent these organized mesoscale circulations and the microphysicallradiative forcing associated with the stratiform region. This issue is generally known as the ‘scale-interaction’ problem that can only be properly addressed in fully three-dimensional simulations. Sensitivity simulations run by several groups showed that the time evolution of the surface convective precipitation was considerably smoothed when the convective closure was based on convective available potential energy instead of moisture convergence. Finally, additional SCM simulations without using a convection parametrization indicated that the impact of a convection parametrization in forced SCM runs was more visible in the moisture profiles than in the temperature profiles because convective transport was particularly important in the moisture budget.
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a gcss model intercomparison for a tropical squall line observed during toga coare i cloud resolving models
Quarterly Journal of the Royal Meteorological Society, 2007Co-Authors: Jean-luc Redelsperger, Francoise Guichard, Thibaut Montmerle, P R A Brown, M Kawasima, Stephen Lang, K Nakamura, Kazuo Saito, Charles J Seman, Leo J DonnerAbstract:Results from eight cloud-resolving models are compared for the first time for the case of an oceanic tropical squall line observed during the Tropical Ocean/Global Atmosphere Coupled Ocean-Atmosphere Response Experiment. There is broad agreement between all the models in describing the overall structure and propagation of the squall line and some quantitative agreement in the evolution of rainfall. There is also a more qualitative agreement between the models in describing the vertical structure of the apparent heat and moisture sources. The three-dimensional (3D) experiments with an active ice phase and open lateral boundary conditions along the direction of the system propagation show good agreement for all parameters. The comparison of 3D simulated fields with those obtained from two different analyses of airborne Doppler radar data indicates that the 3D models are able to simulate the dynamical structure of the squall line, including the observed double-peaked updraughts. However, the second updraught peak at around 10 km in height is obtained only when the ice phase is represented. The 2D simulations with an ice-phase parametrization also exhibit this structure, although with a larger temporal variability. In the 3D simulations, the evolution of the mean wind profile is in the sense of decreasing the shear, but the 2D simulations are unable to reproduce this behaviour.
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a tropical squall line observed during toga coare extended comparisons between simulations and doppler radar data and the role of midlevel wind shear
Monthly Weather Review, 2000Co-Authors: Thibaut Montmerle, Jean-philippe Lafore, Jean-luc RedelspergerAbstract:Abstract Results from a three-dimensional cloud model are extensively compared with airborne Doppler radar data in the case of a tropical oceanic squall line observed during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment. The comparison is based on the precipitation patterns, the dynamical and thermodynamical distributions, and the vertical transport of horizontal momentum. The model simulates the evolution of the mesoscale convective system (MCS) frontal convective line from a quasi-linear to a broken pattern. The area located south of the “break,” which designates the region where the MCS leading edge reorientates from the N–S to the E–W direction, is composed of a pronounced bow-shaped structure with two vortices located on both sides of a strong rear inflow. The vertical circulation is characterized by a jump updraft and an overturning downdraft. Both structures exhibit a vertical, intense updraft in the break zone, whereas the jump updraft is more sloped and less in...
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Modification of Surface Fluxes by Atmospheric Convection in the TOGA COARE Region
Monthly Weather Review, 1996Co-Authors: P. Jabouille, Jean-luc Redelsperger, Jean-philippe LaforeAbstract:Abstract The mesoscale variability of surface heat fluxes induced by atmospheric convection is studied by using 3D cloud explicit simulations and surface observations. Two convective cases observed during the Coupled Ocean–Atmosphere Response Experiment are simulated (26 November 1992 and 17 February 1993) corresponding to different ambient surface wind conditions, namely, light and moderate winds. Numerical results in the first case are successfully compared to surface observations. Local enhancements of two times for the latent heat flux and three times more for the sensible one are produced in the rainy area. Intense wind gusts generated by convective outflow are found mainly responsible for these increases. For the second case, the simulated surface fluxes are found to vary greatly, although they are structured in response to an organized convective system. At the domain scale (90 km × 90 km) corresponding to a general circulation model (GCM) grid box, it is shown that convective activity significantl...