The Experts below are selected from a list of 1002 Experts worldwide ranked by ideXlab platform

Dennis L. Hartmann - One of the best experts on this subject based on the ideXlab platform.

Robert A Houze - One of the best experts on this subject based on the ideXlab platform.

  • in monsoon regions
    2016
    Co-Authors: Jasmine Cetrone, Robert A Houze
    Abstract:

    Anvil Clouds of tropical mesoscale convective system

  • Use of ARM observations and numerical models to determine radiative and latent heating profiles of mesoscale convective systems for general circulation models
    2013
    Co-Authors: Robert A Houze
    Abstract:

    We examined cloud radar data in monsoon climates, using cloud radars at Darwin in the Australian monsoon, on a ship in the Bay of Bengal in the South Asian monsoon, and at Niamey in the West African monsoon. We followed on with a more in-depth study of the continental MCSs over West Africa. We investigated whether the West African Anvil Clouds connected with squall line MCSs passing over the Niamey ARM site could be simulated in a numerical model by comparing the observed Anvil Clouds to Anvil structures generated by the Weather Research and Forecasting (WRF) mesoscale model at high resolution using six different ice-phase microphysical schemes. We carried out further simulations with a cloud-resolving model forced by sounding network budgets over the Niamey region and over the northern Australian region. We have devoted some of the effort of this project to examining how well satellite data can determine the global breadth of the Anvil cloud measurements obtained at the ARM ground sites. We next considered whether satellite data could be objectively analyzed to so that their large global measurement sets can be systematically related to the ARM measurements. Further differences were detailed between the land and ocean MCS Anvilmore » Clouds by examining the interior structure of the Anvils with the satellite-detected the Cloudsat Cloud Profiling Radar (CPR). The satellite survey of Anvil Clouds in the Indo-Pacific region was continued to determine the role of MCSs in producing the cloud pattern associated with the MJO.« less

  • Comparison of Simulated and Observed Continental Tropical Anvil Clouds and Their Radiative Heating Profiles
    Journal of the Atmospheric Sciences, 2012
    Co-Authors: Scott Powell, Robert A Houze, Anil Kumar, Sally A. Mcfarlane
    Abstract:

    AbstractVertically pointing millimeter-wavelength radar observations of Anvil Clouds extending from mesoscale convective systems (MCSs) that pass over an Atmospheric Radiation Measurement Program (ARM) field site in Niamey, Niger, are compared to Anvil structures generated by the Weather Research and Forecasting (WRF) mesoscale model using six different microphysical schemes. The radar data provide the statistical distribution of the radar reflectivity values as a function of height and Anvil thickness. These statistics are compared to the statistics of the modeled Anvil cloud reflectivity at all altitudes. Requiring the model to be statistically accurate at all altitudes is a stringent test of the model performance. The typical vertical profile of radiative heating in the Anvil Clouds is computed from the radar observations. Variability of Anvil structures from the different microphysical schemes provides an estimate of the inherent uncertainty in Anvil radiative heating profiles. All schemes underestima...

  • vertical structures of Anvil Clouds of tropical mesoscale convective systems observed by Cloudsat
    Journal of the Atmospheric Sciences, 2011
    Co-Authors: Jian Yuan, Robert A Houze, Andrew J Heymsfield
    Abstract:

    AbstractA global study of the vertical structures of the Clouds of tropical mesoscale convective systems (MCSs) has been carried out with data from the Cloudsat Cloud Profiling Radar. Tropical MCSs are found to be dominated by cloud-top heights greater than 10 km. Secondary cloud layers sometimes occur in MCSs, but outside their primary raining cores. The secondary layers have tops at 6–8 and 1–3 km. High-topped Clouds extend outward from raining cores of MCSs to form Anvil Clouds. Closest to the raining cores, the Anvils tend to have broader distributions of reflectivity at all levels, with the modal values at higher reflectivity in their lower levels. Portions of Anvil Clouds far away from the raining core are thin and have narrow frequency distributions of reflectivity at all levels with overall weaker values. This difference likely reflects ice particle fallout and therefore cloud age. Reflectivity histograms of MCS Anvil Clouds vary little across the tropics, except that (i) in continental MCS Anvils...

  • leading and trailing Anvil Clouds of west african squall lines
    Journal of the Atmospheric Sciences, 2011
    Co-Authors: Jasmine Cetrone, Robert A Houze
    Abstract:

    AbstractThe Anvil Clouds of tropical squall-line systems over West Africa have been examined using cloud radar data and divided into those that appear ahead of the leading convective line and those on the trailing side of the system. The leading Anvils are generally higher in altitude than the trailing Anvil, likely because the hydrometeors in the leading Anvil are directly connected to the convective updraft, while the trailing Anvil generally extends out of the lower-topped stratiform precipitation region. When the Anvils are subdivided into thick, medium, and thin portions, the thick leading Anvil is seen to have systematically higher reflectivity than the thick trailing Anvil, suggesting that the leading Anvil contains numerous larger ice particles owing to its direct connection to the convective region. As the leading Anvil ages and thins, it retains its top. The leading Anvil appears to add hydrometeors at the highest altitudes, while the trailing Anvil is able to moisten a deep layer of the atmosphere.

Andrew J Heymsfield - One of the best experts on this subject based on the ideXlab platform.

  • Combining In Situ and Satellite Observations to Understand the Vertical Structure of Tropical Anvil Cloud Microphysical Properties During the TC4 Experiment.
    Earth and space science (Hoboken N.J.), 2020
    Co-Authors: Qing Yue, Andrew J Heymsfield, Kuo-nan Liou, Jonathan H. Jiang, Arushi Sinha
    Abstract:

    Tropical Anvil Clouds have a profound impact on Earth's weather and climate. Their role in Earth's energy balance and hydrologic cycle is heavily modulated by the vertical structure of the microphysical properties for various hydrometeors in these Clouds and their dependence on the ambient environmental conditions. Accurate representations of the variability and covariability of such vertical structures are key to both the satellite remote sensing of cloud and precipitation and numerical modeling of weather and climate, which remain a challenge. This study presents a new method to combine vertically resolved observations from Cloudsat radar reflectivity and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation cloud masks with probability distributions of cloud microphysical properties and the ambient atmospheric conditions from detailed in situ measurements on tropical Anvils sampled during the National Aeronautics and Space Administration TC4 (Tropical Composition, Cloud and Climate Coupling) mission. We focus on the microphysical properties of the vertical distribution of ice water content, particle size distributions, and effective sizes for different hydrometeors, including ice particles and supercooled liquid droplets. Results from this method are compared with those from in situ data alone and various Cloudsat/Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation cloud retrievals. The sampling limitation of the field experiment and algorithm limitations in the current retrievals is highlighted, especially for the liquid cloud particles, while a generally good agreement with ice cloud microphysical properties is seen from different methods. While the method presented in this study is applied to tropical Anvil Clouds observed during TC4, it can be readily employed to study a broad range of ice Clouds sampled by various field campaigns.

  • vertical structures of Anvil Clouds of tropical mesoscale convective systems observed by Cloudsat
    Journal of the Atmospheric Sciences, 2011
    Co-Authors: Jian Yuan, Robert A Houze, Andrew J Heymsfield
    Abstract:

    AbstractA global study of the vertical structures of the Clouds of tropical mesoscale convective systems (MCSs) has been carried out with data from the Cloudsat Cloud Profiling Radar. Tropical MCSs are found to be dominated by cloud-top heights greater than 10 km. Secondary cloud layers sometimes occur in MCSs, but outside their primary raining cores. The secondary layers have tops at 6–8 and 1–3 km. High-topped Clouds extend outward from raining cores of MCSs to form Anvil Clouds. Closest to the raining cores, the Anvils tend to have broader distributions of reflectivity at all levels, with the modal values at higher reflectivity in their lower levels. Portions of Anvil Clouds far away from the raining core are thin and have narrow frequency distributions of reflectivity at all levels with overall weaker values. This difference likely reflects ice particle fallout and therefore cloud age. Reflectivity histograms of MCS Anvil Clouds vary little across the tropics, except that (i) in continental MCS Anvils...

  • Evidence of nitric acid uptake in warm cirrus Anvil Clouds during the NASA TC4 campaign
    Journal of Geophysical Research, 2010
    Co-Authors: Eric Scheuer, Andrew J Heymsfield, Jack E. Dibb, Cynthia H. Twohy, David C. Rogers, Aaron Bansemer
    Abstract:

    [1] Uptake of HNO3 onto cirrus ice may play an important role in tropospheric NOx cycling. Discrepancies between modeled and in situ measurements of gas-phase HNO3 in the troposphere suggest that redistribution and removal mechanisms by cirrus ice have been poorly constrained. Limited in situ measurements have provided somewhat differing results and are not fully compatible with theory developed from laboratory studies. We present new airborne measurements of HNO3 in cirrus Clouds from Anvil outflow made during the Tropical Composition, Cloud, and Climate Coupling Experiment (TC4). Upper tropospheric (>9 km) measurements made during three flights while repeatedly traversing the same cloud region revealed depletions of gas-phase HNO3 in regions characterized by higher ice water content and surface area. We hypothesize that adsorption of HNO3 onto cirrus ice surfaces could explain this. Using measurements of cirrus ice surface area density and some assumptions about background mixing ratios of gas-phase HNO3, we estimate molecular coverages of HNO3 on cirrus ice surface in the tropical upper troposphere during the TC4 racetracks to be about 1 × 1013 molecules cm−2. This likely reflects an upper limit because potential dilution by recently convected, scavenged air is ignored. Also presented is an observation of considerably enhanced gas-phase HNO3 at the base of a cirrus Anvil suggesting vertical redistribution of HNO3 by sedimenting cirrus particles and subsequent particle sublimation and HNO3 evaporation. The impact of released HNO3, however, appears to be restricted to a very thin layer just below the cloud.

  • examinations of ice formation processes in florida cumuli using ice nuclei measurements of Anvil ice crystal particle residues
    Journal of Geophysical Research, 2007
    Co-Authors: A J Prenni, Michael R. Poellot, Cynthia H. Twohy, David C. Rogers, Sonia M. Kreidenweis, Paul J. Demott, Sarah D Brooks, Mathews S Richardson, Andrew J Heymsfield
    Abstract:

    [1] A continuous flow diffusion chamber (CFDC) was used to measure ice formation by cloud particle residuals during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment. These measurements were directed toward determining the relative contributions of homogeneous nucleation, heterogeneous nucleation, and secondary ice formation processes to the concentrations of ice crystals in Anvil cirrus formed from convection. The CFDC sampled residual particles remaining after evaporation of cloud particles initially collected by a counterflow virtual impactor. This allowed, for the first time, determination of the ice nucleation ability of particles that included the presumed nuclei for cloud-ice formation. The approach proved successful for estimating concentrations of heterogeneous ice nuclei (IN) transported into Anvil Clouds, but experimental issues limited measurements of homogeneous freezing and, consequently, in determining the role of secondary ice formation. Results suggest agreement within a factor of 2–3 between CFDC heterogeneous IN concentrations and Anvil ice crystal concentrations in the size range above 30 mm. IN concentrations also correlated with ice concentrations inferred from measurements by the FSSP (Forward Scattering Spectrometer Probe). However, measured IN concentrations were nearly two orders of magnitude lower than FSSP concentrations. This difference may have resulted from homogeneous freezing, secondary ice formation, or other unidentified ice formation processes that were not fully captured by the CFDC. The data suggest that heterogeneous nucleation played a smaller role than homogeneous nucleation in determining Anvil ice crystal concentrations, except during periods of strong desert dust ingestion by cumuli. Nevertheless, heterogeneous nucleation may provide the source for larger ice crystals present in Anvil regions.

  • Evidence for the Predominance of Mid-Tropospheric Aerosols as Subtropical Anvil Cloud Nuclei
    Science (New York N.Y.), 2004
    Co-Authors: Ann M. Fridlind, Andrew J Heymsfield, Andrew S. Ackerman, Eric J. Jensen, Michael R. Poellot, David E. Stevens, Donghai Wang, Larry M. Miloshevich, Darrel Baumgardner, R. Paul Lawson
    Abstract:

    NASA's recent Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment focused on Anvil cirrus Clouds, an important but poorly understood element of our climate system. The data obtained included the first comprehensive measurements of aerosols and cloud particles throughout the atmospheric column during the evolution of multiple deep convective storm systems. Coupling these new measurements with detailed cloud simulations that resolve the size distributions of aerosols and cloud particles, we found several lines of evidence indicating that most Anvil crystals form on mid-tropospheric rather than boundary-layer aerosols. This result defies conventional wisdom and suggests that distant pollution sources may have a greater effect on Anvil Clouds than do local sources.

Kristin Larson - One of the best experts on this subject based on the ideXlab platform.

  • An important constraint on tropical cloud ‐ climate feedback
    Geophysical Research Letters, 2002
    Co-Authors: Dennis L. Hartmann, Kristin Larson
    Abstract:

    [1] Tropical convective Anvil Clouds detrain preferentially near 200 hPa. It is argued here that this occurs because clear-sky radiative cooling decreases rapidly near 200 hPa. This rapid decline of clear-sky longwave cooling occurs because radiative emission from water vapor becomes inefficient above 200 hPa. The emission from water vapor becomes less important than the emission from CO2 because the saturation vapor pressure is so very low at the temperatures above 200 hPa. This suggests that the temperature at the detrainment level, and consequently the emission temperature of tropical Anvil Clouds, will remain constant during climate change. This constraint has very important implications for the potential role of tropical convective Clouds in climate feedback, since it means that the emission temperatures of tropical Anvil Clouds and upper tropospheric water vapor are essentially independent of the surface temperature, so long as the tropopause is colder than the temperature where emission from water vapor becomes relatively small.

  • an important constraint on tropical cloud climate feedback
    Geophysical Research Letters, 2002
    Co-Authors: Dennis L. Hartmann, Kristin Larson
    Abstract:

    [1] Tropical convective Anvil Clouds detrain preferentially near 200 hPa. It is argued here that this occurs because clear-sky radiative cooling decreases rapidly near 200 hPa. This rapid decline of clear-sky longwave cooling occurs because radiative emission from water vapor becomes inefficient above 200 hPa. The emission from water vapor becomes less important than the emission from CO2 because the saturation vapor pressure is so very low at the temperatures above 200 hPa. This suggests that the temperature at the detrainment level, and consequently the emission temperature of tropical Anvil Clouds, will remain constant during climate change. This constraint has very important implications for the potential role of tropical convective Clouds in climate feedback, since it means that the emission temperatures of tropical Anvil Clouds and upper tropospheric water vapor are essentially independent of the surface temperature, so long as the tropopause is colder than the temperature where emission from water vapor becomes relatively small.

Jacob T. Seeley - One of the best experts on this subject based on the ideXlab platform.

  • FAT or FiTT: Are Anvil Clouds or the Tropopause Temperature Invariant?
    Geophysical Research Letters, 2019
    Co-Authors: Jacob T. Seeley, Nadir Jeevanjee, David M. Romps
    Abstract:

    Author(s): Seeley, JT; Jeevanjee, N; Romps, DM | Abstract: ©2019. American Geophysical Union. All Rights Reserved. The Fixed Anvil Temperature (FAT) hypothesis proposes that upper tropospheric cloud fraction peaks at a special isotherm that is independent of surface temperature. It has been argued that a FAT should result from simple ingredients: Clausius-Clapeyron, longwave emission from water vapor, and tropospheric energy and mass balance. Here the first cloud-resolving simulations of radiative-convective equilibrium designed to contain only these basic ingredients are presented. This setup does not produce a FAT: the Anvil temperature varies by about 40% of the surface temperature range. However, the tropopause temperature varies by only 4% of the surface temperature range, which supports the existence of a Fixed Tropopause Temperature (FiTT). In full-complexity radiative-convective equilibrium simulations, the spread in Anvil temperature is smaller by about a factor of 2, but the tropopause temperature remains more invariant than the Anvil temperature by an order of magnitude. In other words, our simulations have a FiTT, not a FAT.

  • Formation of Tropical Anvil Clouds by Slow Evaporation
    Geophysical Research Letters, 2019
    Co-Authors: Jacob T. Seeley, Nadir Jeevanjee, Wolfgang Langhans, David M. Romps
    Abstract:

    ©2019. American Geophysical Union. All Rights Reserved. Tropical Anvil Clouds play a large role in the Earth's radiation balance, but their effect on global warming is uncertain. The conventional paradigm for these Clouds attributes their existence to the rapidly declining convective mass flux below the tropopause, which implies a large source of detraining cloudy air there. Here we test this paradigm by manipulating the sources and sinks of cloudy air in cloud-resolving simulations. We find that Anvils form in our simulations because of the long lifetime of upper-tropospheric cloud condensates, not because of an enhanced source of cloudy air below the tropopause. We further show that cloud lifetimes are long in the cold upper troposphere because the saturation specific humidity is much smaller there than the condensed water loading of cloudy updrafts, which causes evaporative cloud decay to act very slowly. Our results highlight the need for novel cloud-fraction schemes that align with this decay-centric framework for Anvil Clouds.

  • FAT or FiTT: Are Anvil Clouds or the tropopause temperature-invariant? (manuscript data)
    2019
    Co-Authors: Jacob T. Seeley
    Abstract:

    Cloud-resolving model output used in the manuscript "FAT or FiTT: Are Anvil Clouds or the tropopause temperature-invariant?" by Seeley et al

  • Formation of tropical Anvil Clouds by slow evaporation (manuscript data)
    2018
    Co-Authors: Jacob T. Seeley
    Abstract:

    Cloud-resolving model output used in the manuscript "Formation of tropical Anvil Clouds by slow evaporation" by Seeley et al