Rabindra Palikonda

Transformation of contrails into cirrus during SUCCESS

Three contrail systems were analyzed with geostationary satellite data to document the conversion of the contrails to cirrus clouds. Two unique contrails, a pair of figure eights and a NASA DC-8 oval, were tracked for more than 7 hours. A cluster of contrails from commercial aircraft lasted over 17 hours. The figure eights produced a cirrus cloud having a maximum extent of 12,000 km²; the commercial cluster reached an area of ∼35,000 km². The contrail-cirrus were thin with optical depths between 0.2 and 0.5. In all cases, cloud particle size increased as the contrails developed into cirrus clouds. The climatic impact of contrails will be greater than would be estimated if only linear contrails, those typically observed in satellite imagery, are considered. Additional research is required to obtain reliable statistics on contrail growth and lifetime.

CERES Edition-2 Cloud Property Retrievals Using TRMM VIRS and Terra and Aqua MODIS Data—Part II: Examples of Average Results and Comparisons With Other Data

Cloud properties were retrieved by applying the Clouds and Earths Radiant Energy System (CERES) project Edition-2 algorithms to 3.5 years of Tropical Rainfall Measuring Mission Visible and Infrared Scanner data and 5.5 and 8 years of MODerate Resolution Imaging Spectroradiometer (MODIS) data from Aqua and Terra, respectively. The cloud products are consistent quantitatively from all three imagers; the greatest discrepancies occur over ice-covered surfaces. The retrieved cloud cover (~59%) is divided equally between liquid and ice clouds. Global mean cloud effective heights, optical depth, effective particle sizes, and water paths are 2.5 km, 9.9, 12.9 μm , and 80 g·m-2, respectively, for liquid clouds and 8.3 km, 12.7, 52.2 μm, and 230 g·m-2 for ice clouds. Cloud droplet effective radius is greater over ocean than land and has a pronounced seasonal cycle over southern oceans. Comparisons with independent measurements from surface sites, the Ice Cloud and Land Elevation Satellite, and the Aqua Advanced Microwave Scanning Radiometer-Earth Observing System are used to evaluate the results. The mean CERES and MODIS Atmosphere Science Team cloud properties have many similarities but exhibit large discrepancies in certain parameters due to differences in the algorithms and the number of unretrieved cloud pixels. Problem areas in the CERES algorithms are identified and discussed.

Contrail coverage derived from 2001 AVHRR data over the continental United States of America and surrounding areas

Linear contrail coverage, optical depth, and longwave radiative forcing are derived from NOAA-15 and NOAA-16 Advanced Very High Resolution Radiometer data taken during daytime over the continental United States of America (USA), southern Canada, northern Mexico, and the adjacent oceans. Analyses were performed for all available overpasses during 2001, but for NOAA-15 were primarily limited to the eastern half and the northwestern corner of the domain. Contrail coverage averaged 1.17 % and 0.65 % from the early morning NOAA-15 and midafternoon NOAA-16, respectively, for the areas and month common to both satellites. The NOAA-16 contrail coverage and radiative properties for the limited NOAA-15 domain are, on average, nearly identical to those for the entire domain. The estimated combined maximum coverage for the entire domain was ∼1.05 % during February, while the minimum of 0.57 % occurred during August. Mean optical depths varied by ∼ 20 % with winter minima and summer maxima. The annual mean optical depth of 0.27 translated to a normalized contrail longwave radiative forcing of 15.5 Wm -2 . The overall daytime longwave radiative forcing for the domain is 0.11 Wm -2 . The normalized radiative forcing peaked during summer while the overall forcing was at a maximum during winter because of the greater contrail coverage. A detailed error analysis showed that the linear contrail coverage was overestimated by ∼40 % for both satellites the true coverage is closer to 0.70 and 0.40 % for NOAA-15 and 16, respectively. Errors in the mean NOAA-15 optical depths and radiative forcing were negligible while their NOAA-16 counterparts were overestimated by approximately 13 %. Contrail coverage was dramatically lower than expected from previous studies, but is most likely due to the significant decrease in upper tropospheric humidity observed in numerical weather analysis data. Contrail optical depths are much greater than both theoretical estimates for this part of North America and empirical retrievals over Europe. The cause of the morning-afternoon difference in contrail coverage is not yet known. Further modelling studies and additional satellite analyses are needed to understand this diurnal cycle and to explain the differences between the present and previous results.

Estimation of water cloud properties from satellite microwave, infrared and visible measurements in oceanic environments: 2. Results

A microwave (MW) method for deriving cloud liquid water path (LWP) and cloud water temperature (Tw) is validated by using soundings and results from a visible (VIS) and infrared (IR) retrieval method. The two retrieval methods are combined into a single technique, MVI (microwave, visible, and infrared), to estimate the frequency of multilayered clouds and the effective droplet radius re in water clouds. These techniques were applied to Meteosat and special sensor microwave/imager (SSM/I) data taken during June 1–28, 1992, over the Atlantic Stratocumulus Transition Experiment (ASTEX) region. For low clouds, as identified with the VIS-IR method, Tw on average is nearly the same as the VIS-IR cloud-top temperatures (Tc). A negative correlation between LWP and Tc was found for the clouds. For midlevel clouds, Tw is about 8 K warmer than Tc because of either large cloud thicknesses or multilayered clouds. When high clouds are found by the VIS-IR method, Tc is ∼30 K colder than Tw, indicating that lower-level liquid-water clouds may be detected by the MW method. On the basis of the matched Tw and Tc obsevations, the estimated frequencies of multilayered high, middle, and low clouds are about 36%, 19%, and 0%, respectively, values that are similar to cloud radar measurements. Matched satellite and ground-based radar data show that the MVI technique can separate cloud layers when high ice clouds overlap lower liquid water clouds. The distributions of re for water clouds are about the same for low, middle, and broken clouds with mean and standard deviations of ∼12 and 10 μm, respectively. The frequency of large droplets (re>16 μm) suggests that drizzle occurs in ∼30% of the matched Meteosat-SSM/I cloudy conditions.

A case study of the development of contrail clusters over the Great Lakes

Abstract Widespread persistent contrails over the western Great Lakes during 9 October 2000 were examined using commercial flight data, coincident meteorological data, and satellite remote sensing data from several platforms. The data were analyzed to determine the atmospheric conditions under which the contrails formed and to measure several physical properties of the contrails, including areal coverage, spreading rates, fall speeds, and optical properties. Most of the contrails were located between 10.6 and 11.8 km in atmospheric conditions consistent with a modified form of the Appleman contrail formation theory. However, the Rapid Update Cycle-2 analyses have a dry bias in the upper-tropospheric relative humidity with respect to ice (RHI), as indicated by persistent contrail generation during the outbreak where RHI ≥ 85%. The model analyses show that synoptic-scale vertical velocities affect the formation of persistent contrails. Areal coverage by linear contrails peaked at 30 000 km2, but the maximum...

Near-real time cloud retrievals from operational and research meteorological satellites

A set of cloud retrieval algorithms developed for CERES and applied to MODIS data have been adapted to analyze other satellite imager data in near-real time. The cloud products, including single-layer cloud amount, top and base height, optical depth, phase, effective particle size, and liquid and ice water paths, are being retrieved from GOES- 10/11/12, MTSAT-1R, FY-2C, and Meteosat imager data as well as from MODIS. A comprehensive system to normalize the calibrations to MODIS has been implemented to maximize consistency in the products across platforms. Estimates of surface and top-of-atmosphere broadband radiative fluxes are also provided. Multilayered cloud properties are retrieved from GOES-12, Meteosat, and MODIS data. Native pixel resolution analyses are performed over selected domains, while reduced sampling is used for full-disk retrievals. Tools have been developed for matching the pixel-level results with instrumented surface sites and active sensor satellites. The calibrations, methods, examples of the products, and comparisons with the ICESat GLAS lidar are discussed. These products are currently being used for aircraft icing diagnoses, numerical weather modeling assimilation, and atmospheric radiation research and have potential for use in many other applications.

Clouds, Aerosol, and Precipitation in the Marine Boundary Layer: An ARM Mobile Facility Deployment

© Copyright 2015 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act September 2010 Page 2 or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a web site or in a searchable database, or other uses of this material, except as exempted by the above statement, requires written permission or a license from the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at (https://www.ametsoc.org/) or from the AMS at 617-227-2425 or copyrights@ametsoc.org.

Contrail properties over the eastern North Pacific from AVHRR data

An increase of air traffic over the North Pacific during the last 30 years has been accompanied by an increase in cirrus coverage. To help alleviate the uncertainty in the contribution of air traffic to the cirrus increase, an analysis of linear contrail coverage over the region has been initiated using afternoon NOAA-16 AVHRR data taken during 4 months in 2002 and 2003. Manual evaluation of the automated contrail detection method revealed that it misclassified, on average, 32 % of the pixels as contrails and missed 15 % of the contrail pixels. After correction for detection errors, the contrail coverage over the domain between 25 o and 55 o N and between 120 o and 150 o W varied from a minimum of 0.37 % in February to a maximum of 0.56 % in May, respectively. The annual mean coverage, after correcting for the diurnal cycle of air traffic, is 0.31 %, a value very close to earlier theoretical estimates for the region. Contrail optical depths for the 4 months average 0.24 resulting in a mean unit contrail longwave radiative forcing of 14.2 Wm -2 . The contrail optical depths are twice the mean value expected from theoretical estimates.

Mean Structure and Diurnal Cycle of Southeast Atlantic Boundary Layer Clouds: Insights from Satellite Observations and Multiscale Modeling Framework Simulations

AbstractThe mean structure and diurnal cycle of southeast (SE) Atlantic boundary layer clouds are described with satellite observations and multiscale modeling framework (MMF) simulations during austral spring (September–November). Hourly resolution cloud fraction (CF) and cloud-top height (HT) are retrieved from Meteosat-9 radiances using modified Clouds and the Earth’s Radiant Energy System (CERES) Moderate Resolution Imaging Spectroradiometer (MODIS) algorithms, whereas liquid water path (LWP) is from the University of Wisconsin microwave satellite climatology. The MMF simulations use a 2D cloud-resolving model (CRM) that contains an advanced third-order turbulence closure to explicitly simulate cloud physical processes in every grid column of a general circulation model. The model accurately reproduces the marine stratocumulus spatial extent and cloud cover. The mean cloud cover spatial variability in the model is primarily explained by the boundary layer decoupling strength, whereas a boundary layer ...

Cloud coverage and height during FIRE ACE derived from AVHRR data

Cloud cover and height are derived from NOAA-12 and NOAA-14 advanced very high resolution radiometer (AVHRR) data taken over the Arctic Ocean for an 8° latitude by 30° longitude domain centered on the Surface Heat Budget of the Arctic Ocean (SHEBA) ship Des Groseilliers. Multispectral thresholds were determined subjectively and applied to each image, providing excellent temporal coverage during the May-July 1998 First ISCCP Regional Experiment Arctic Clouds Experiment (FIRE ACE). Mean cloud amounts were near 70% for the entire period but varied regionally from 55 to 85%. On the basis of a limited climatology of ship observations, these values appear to be typical for this part of the Arctic, suggesting that most of FIRE ACE was conducted in representative cloud conditions. A diurnal cycle of mean cloud amount was found for the domain during June and July having a range of 10% with a middle-to-late morning maximum. The AVHRR-derived cloud amounts are in good agreement with visual and radar measurements taken from the Des Groseilliers, except for a few subvisual and low cloud cases. Average AVHRR-derived cloudiness differ from the mean values obtained at the surface by −1 to +3%; this represents a significant improvement over previous satellite retrievals. The satellite-derived cloud heights are very accurate for most of the low cloud cases. Higher cloud altitudes are less certain because cloud optical depths were not available to adjust the temperature observed for the optically thin high clouds, and the radiating temperature of many of the high clouds is representative of some altitude deep in the cloud rather than the highest altitude level of condensate. The development of a more accurate automated algorithm for detecting polar clouds at AVHRR wavelengths will require inclusion of variable thresholds to account for the angular dependence of the surface reflectance as well as the seasonally changing albedos of the ice pack. The use of a 1.6-μm channel on the AVHRR, or other complement of instruments, will greatly enhance the capabilities for detecting clouds over poles during summer.