Andrew J. Heymsfield

Indian Ocean Experiment: An integrated analysis of the climate forcing and effects of the great Indo-Asian haze

Every year, from December to April, anthropogenic haze spreads over most of the North Indian Ocean, and South and Southeast Asia. The Indian Ocean Experiment (INDOEX) documented this Indo-Asian haze at scales ranging from individual particles to its contribution to the regional climate forcing. This study integrates the multiplatform observations (satellites, aircraft, ships, surface stations, and balloons) with one- and four-dimensional models to derive the regional aerosol forcing resulting from the direct, the semidirect and the two indirect effects. The haze particles consisted of several inorganic and carbonaceous species, including absorbing black carbon clusters, fly ash, and mineral dust. The most striking result was the large loading of aerosols over most of the South Asian region and the North Indian Ocean. The January to March 1999 visible optical depths were about 0.5 over most of the continent and reached values as large as 0.2 over the equatorial Indian ocean due to long-range transport. The aerosol layer extended as high as 3 km. Black carbon contributed about 14% to the fine particle mass and 11% to the visible optical depth. The single-scattering albedo estimated by several independent methods was consistently around 0.9 both inland and over the open ocean. Anthropogenic sources contributed as much as 80% (±10%) to the aerosol loading and the optical depth. The in situ data, which clearly support the existence of the first indirect effect (increased aerosol concentration producing more cloud drops with smaller effective radii), are used to develop a composite indirect effect scheme. The Indo-Asian aerosols impact the radiative forcing through a complex set of heating (positive forcing) and cooling (negative forcing) processes. Clouds and black carbon emerge as the major players. The dominant factor, however, is the large negative forcing (-20±4 W m^(−2)) at the surface and the comparably large atmospheric heating. Regionally, the absorbing haze decreased the surface solar radiation by an amount comparable to 50% of the total ocean heat flux and nearly doubled the lower tropospheric solar heating. We demonstrate with a general circulation model how this additional heating significantly perturbs the tropical rainfall patterns and the hydrological cycle with implications to global climate.

A Parameterization of the Particle Size Spectrum of Ice Clouds in Terms of the Ambient Temperature and the Ice Water Content

Abstract A data set obtained in cirrus clouds has been examined to deduce any dependencies of the particle size spectral form or the crystal habit on the temperature. It was found that both form of the spectra and crystal habit changed systematically with temperature, the largest change occurring between −l40 and −50°C. These findings are consistent with previously found dependencies between linear backscatter measurements and temperature. A preliminary scheme for parameterizing the cirrus particle size spectra for crystal dimensions greater than 20 μm in terms of the temperature and the ice water content is described. The visible extinction in cirrus is estimated.

Microphysical Characteristics of Three Anvils Sampled during the Central Equatorial Pacific Experiment

Abstract In situ microphysical measurements of three anvils were made 17 March, 1 April, and 4 April 1993 during the Central Equatorial Pacific Experiment for several constant altitude penetrations, in the same direction or opposite the ambient wind, from 7 to 14 km. Ice water contents (IWCs), derived from an optical array probe, increased downward in the anvil; concentrations also increased, but not as quickly. Median mass dimensions, defined as the ice crystal maximum dimension below which half of the mass is contained, increased from averages of less than 0.1 mm near the tops to averages of about 0.5 mm near the bases. Substantial variations in cloud parameters occurred in the horizontal direction as well, with larger IWCs and concentrations closer to the convective core and its remnants. Small crystals were measured and categorized according to their shapes with the Video Ice Particle Sampler, which detects particles with dimensions greater than 5 µm. For small IWCs, especially prevalent at cloud tops...

The Mixed-Phase Arctic Cloud Experiment

The Mixed-Phase Arctic Cloud Experiment (M-PACE) was conducted from 27 September through 22 October 2004 over the Department of Energys Atmospheric Radiation Measurement (ARM) Climate Research Facility (ACRF) on the North Slope of Alaska. The primary objectives were to collect a dataset suitable to study interactions between microphysics, dynamics, and radiative transfer in mixed-phase Arctic clouds, and to develop/evaluate cloud property retrievals from surface-and satellite-based remote sensing instruments. Observations taken during the 1977/98 Surface Heat and Energy Budget of the Arctic (SHEBA) experiment revealed that Arctic clouds frequently consist of one (or more) liquid layers precipitating ice. M-PACE sought to investigate the physical processes of these clouds by utilizing two aircraft (an in situ aircraft to characterize the microphysical properties of the clouds and a remote sensing aircraft to constraint the upwelling radiation) over the ACRF site on the North Slope of Alaska. The measureme...

Shattering and Particle Interarrival Times Measured by Optical Array Probes in Ice Clouds

Abstract Optical array probes are one of the most important tools for determining the microphysical structure of clouds. It has been known for some time that the shattering of ice crystals on the housing of these probes can lead to incorrect measurements of particle size distributions and subsequently derived microphysical properties if the resulting spurious particles are not rejected. In this paper it is shown that the interarrival times of particles measured by these probes can be bimodal—the “cloud” probes are more affected than the “precipitation” probes. The long interarrival time mode represents real cloud structure while the short interarrival time mode results from fragments of shattered ice particles. It is demonstrated for the flights considered here that if the fragmented particles are filtered using an interarrival time threshold of 2 × 10−4 s in three of the four cases and 1 × 10−5 s in the other, then the measured total concentration can be affected by up to a factor of 4 in situations wher...

Observations and Parameterizations of Particle Size Distributions in Deep Tropical Cirrus and Stratiform Precipitating Clouds: Results from In Situ Observations in TRMM Field Campaigns

Abstract This study reports on the evolution of particle size distributions (PSDs) and habits as measured during slow, Lagrangian-type spiral descents through deep subtropical and tropical cloud layers in Florida, Brazil, and Kwajalein, Marshall Islands, most of which were precipitating. The objective of the flight patterns was to learn more about how the PSDs evolved in the vertical and to obtain information of the vertical structure of microphysical properties. New instrumentation yielding better information on the concentrations of particles in the size (D) range between 0.2 and 2 cm, as well as improved particle imagery, produced more comprehensive observations for tropical stratiform precipitation regions and anvils than have been available previously. Collocated radar observations provided additional information on the vertical structure of the cloud layers sampled. Most of the spirals began at cloud top, with temperatures (T) as low as −50°C, and ended at cloud base or below the melting layer (ML)....

Production of ice in tropospheric clouds: A review

Ice in the troposphere affects a variety of processes, including the formation of precipitation, and cloud lifetime, albedo, dynamics, and electrification. A lack of understanding of the ways in which ice is created and multiplied hampers progress in understanding all of these processes. We survey the state of knowledge, starting with homogeneous nucleation, where current formulations for freezing from both pure water and solutions have considerable predictive power. However, debate still exists on the underlying mechanisms of nucleation. Using the concepts and framework that homogeneous nucleation provides, heterogeneous nucleation, where neither a commonly agreed upon theory nor even standard measurement technique exists, is considered. Investigators have established the ice-nucleating characteristics of broad classes of substances, such as mineral dust and soot, which are important ice nuclei in t he atmosphere, but a coherent theory of why these substances act as they do has yet to emerge. All ice in ...

Bulk Scattering Properties for the Remote Sensing of Ice Clouds. Part II: Narrowband Models

Abstract This study examines the development of bulk single-scattering properties of ice clouds, including single-scattering albedo, asymmetry factor, and phase function, for a set of 1117 particle size distributions obtained from analysis of the First International Satellite Cloud Climatology Project Regional Experiment (FIRE)-I, FIRE-II, Atmospheric Radiation Measurement Program intensive observation period, Tropical Rainfall Measuring Mission Kwajalein Experiment (KWAJEX), and the Cirrus Regional Study of Tropical Anvils and Cirrus Layers (CRYSTAL) Florida Area Cirrus Experiment (FACE) data. The primary focus is to develop band-averaged models appropriate for use by the Moderate Resolution Imaging Spectroradiometer (MODIS) imager on the Earth Observing System Terra and Aqua platforms, specifically for bands located at wavelengths of 0.65, 1.64, 2.13, and 3.75 μm. The results indicate that there are substantial differences in the bulk scattering properties of ice clouds formed in areas of deep convectio...

Bulk Scattering Properties for the Remote Sensing of Ice Clouds. Part I: Microphysical Data and Models

This study reports on the use of in situ data obtained in midlatitude and tropical ice clouds from airborne sampling probes and balloon-borne replicators as the basis for the development of bulk scattering models for use in satellite remote sensing applications. Airborne sampling instrumentation includes the twodimensional cloud (2D-C), two-dimensional precipitation (2D-P), high-volume precipitation spectrometer (HVPS), cloud particle imager (CPI), and NCAR video ice particle sampler (VIPS) probes. Herein the development of a comprehensive set of microphysical models based on in situ measurements of particle size distributions (PSDs) is discussed. Two parameters are developed and examined: ice water content (IWC) and median mass diameter Dm. Comparisons are provided between the IWC and Dm values derived from in situ measurements obtained during a series of field campaigns held in the midlatitude and tropical regions and those calculated from a set of modeled ice particles used for light-scattering calculations. The ice particle types considered in this study include droxtals, hexagonal plates, solid columns, hollow columns, aggregates, and 3D bullet rosettes. It is shown that no single habit accurately replicates the derived IWC and Dm values, but a mixture of habits can significantly improve the comparison of these bulk microphysical properties. In addition, the relationship between Dm and the effective particle size Deff, defined as 1.5 times the ratio of ice particle volume to projected area for a given PSD, is investigated. Based on these results, a subset of microphysical models is chosen as the basis for the development of ice cloud bulk scattering models in Part II of this study.

Parameterization of Tropical Cirrus Ice Crystal Size Distributions and Implications for Radiative Transfer: Results from CEPEX

Average ice crystal size distributions are parameterized as functions of temperature and ice water content (IWC), based on observations in cirrus produced as outflows of deep convection made during the Central Equatorial Pacific Experiment (CEPEX), as the sum of a first-order gamma function, describing ice crystals with melted equivalent diameters (Dm) less than 100 mm, and a lognormal function, describing larger ice crystals. The fit parameters are chosen to minimize the chi-squared function describing the difference between observed and parameterized distribution functions. The parameterization is mass conserving, accurately represents small ice crystals, and is easily integrable. The parameterization gives accurate estimates of mass, area, and number contained in different size ranges. The radiative properties estimated from midlatitude parameterizations are compared with those estimated from this parameterization using anomalous diffraction theory. As opposed to some previous studies, small crystals do not dominate the mass and radiative properties of cirrus. Comparison with midlatitude observations shows that size distribution shape can vary substantially depending on where, when, and how the cirrus is measured and on how it forms.