Polar Mesospheric Clouds (PMCs) Observed by the Ozone Monitoring Instrument (OMI) on Aura

Backscattered ultraviolet (BUV) instruments designed for measuring stratospheric ozone profiles have proven to be robust tools for observing polar mesospheric clouds (PMCs). These measurements are available for more than 30 years, and have been used to demonstrate the existence of long-term variations in PMC occurrence frequency and brightness. The Ozone Monitoring Instrument (OMI) on the EOS Aura satellite provides new and improved capabilities for PMC characterization. OMI uses smaller pixels than previous BUV instruments, which increases its ability to identify PMCs and discern more spatial structure, and its wide cross-track viewing swath provides full polar coverage up to 90 latitude every day in both hemispheres. This cross-track coverage allows the evolution of PMC regions to be followed over several consecutive orbits. Localized PMC variations determined from OMI measurements are consistent with coincident SBUV/2 measurements. Nine seasons of PMC observations from OMI are now available, and clearly demonstrate the advantages of these measurements for PMC analysis

Cloud Remote Sensing Using Midwave IR CO2 and N2O Slicing Channels near 4.5 μm

Abstract: Narrow channels located in the longwave IR CO2 absorption region between approximately 13.2 and 14.5 μm, the well known CO2 slicing channels, have been proven to be quite effective for the estimates of cloud heights and effective cloud amounts as well as atmospheric temperature profiles. The designs of some of the near-future multi-channel earth observing satellite sensors cannot accommodate these longwave IR channels. Based on the analysis of the multi-channel imaging data collected with the NASA Moderate Resolution Imaging SpectroRadiometer (MODIS) instrument and on theoretical cloud radiative transfer modeling, we have found that narrow channels located at the midwave IR region between approximately 4.2 and 4.55 μm, where the combined CO2 and N2O absorption effects decrease rapidly with increasing wavelength, have similar properties as the longwave IR CO2 slicing channels. The scattering of solar radiation by clouds on the long wavelength side of the 4.3 μm CO2 absorption makes only a small contribution to the upwelling radiances. In order to retain the crucial cloud and temperature sensing capabilities, future satellite sensors should consider including midwave IR CO2 and N2O slicing channels if the longwave IR channels cannot be implemented on the sensors. The hyperspectral data covering the 3.7�15.5 �m wavelength range and measured with the Infrared Atmospheric Sounding Interferometer (IASI) can be used to further assess the utility of midwave IR channels for satellite remote sensing. Remote Sens. 2011, 3 100

Direct Observations of PMC Local Time Variations by Aura OMI

The Ozone Monitoring Instrument (OMI) on the Aura satellite obtains unique measurements for polar mesospheric cloud (PMC) analysis. Its wide cross-track viewing swath and high along-track spatial resolution makes it possible to directly evaluate PMC occurrence frequency and brightness variations between 6S" and 8S' latitude as a function of local time over a 12-14 h continuous period. OMI PMC local time variations are closely coupled to concurrent variations in measurement scattering angle, so that ice phase function effects must be considered when interpreting the observations. Two different phase functions corresponding to bright and faint clouds are examined in this analysis. OMI observations show maximum frequency and albedo values at 8-10 h local time in the Northern Hemisphere, with decreasing amplitude at higher latitudes. Southern Hemisphere values reach a minimum at 18-20 h LT. Larger variations are seen in Northern Hemisphere data. No statistically significant longitudinal dependence was seen

Spectral Measurements of PMCs from SBUV/2 Instruments

The SBUV/2 (Solar Backscattered Ultraviolet, model 2) instrument is designed to monitor ozone stratospheric profile and total column ozone using measurements of the Earth's backscattered ultraviolet albedo. We have previously demonstrated that the normal radiance measurements from SBUV/2 instruments, which sample 12 discrete wavelengths between 252 and 340 nm during each scan, can be used to identify polar mesospheric clouds (PMCs). Some SBUV/2 instruments also periodically view the earth in continuous scan mode, covering the wavelength range 160-400 nm with 0.15 nm sampling. Analysis of these data show PMC occurrence rates similar to the normal discrete scan results, although the observation technique reduces the number of daily measurements by a factor of six. PMC observed by SBUV/2 instruments show a monotonic variation in the residual spectral albedo over the wavelength range 250 300 nm, with maximum enhancements of 10 15% at 250 nm. This result is consistent with microphysical model predictions from Jensen [1989. A numerical model of polar mesospheric cloud formation and evolution, Ph. D. Thesis, University of Colorado]. We find no evidence for a systematic localized increase in PMC residual albedo for wavelengths near 260 nm, in contrast to the recently reported results from the MSX UVISI instrument [Carbary J.F., et al., 2004. Evidence for bimodal particle distribution from the spectra of polar mesospheric clouds. Geophysics Research. Letters 31, L13108]. This result is observed for three different SBUV/2 instruments in both Northern and Southern Hemisphere data over a 13-year span. Our Mie scattering calculations show that the location and magnitude of the 260 nm hump feature is dependent upon the specific scattering angles appropriate to the MSX measurements. Although it explains the MSX spectrum, the bimodal size distribution proposed by Carbary et al. (2004), cannot explain the lack of scattering angle dependence of the SBUV/2 spectral shapes. The spectral signature of the SBUV/2 continuous scan PMC data is thus inconsistent with the bimodal particle size distribution suggested by Carbary et al. (2004)

Models for the aerosols of the lower atmosphere and the effects of humidity variations on their optical properties /

Aerosol models have been developed for the lower atmosphere. These models are representative of conditions found in rural, urban, and maritime air masses. The changes in the aerosol properties with variations in the relative humidity are discussed. To describe the aerosol optical properties in the extreme of 100 percent relative humidity, several fog models are presented. For each model the coefficients for extinction, scattering, and absorption, the angular scattering distribution, and other optical parameters have been computed for wavelengths between 0.2 and 40 microns. These aerosol models are presented together with a review of their experimental basis. The optical properties of these models are discussed and some comparisons of the model with experimental measurements are presented.Research supported by the Air Force Geophysics Laboratory, Air Force Systems Command, United States Air Force, Hanscom AFB, Massachusetts.Optical Physics Division Project 7670.Chiefly tables.ADA085951 (from http://www.dtic.mil)."20 September 1979."Includes bibliographical references (pages 89-94).Aerosol models have been developed for the lower atmosphere. These models are representative of conditions found in rural, urban, and maritime air masses. The changes in the aerosol properties with variations in the relative humidity are discussed. To describe the aerosol optical properties in the extreme of 100 percent relative humidity, several fog models are presented. For each model the coefficients for extinction, scattering, and absorption, the angular scattering distribution, and other optical parameters have been computed for wavelengths between 0.2 and 40 microns. These aerosol models are presented together with a review of their experimental basis. The optical properties of these models are discussed and some comparisons of the model with experimental measurements are presented.Mode of access: Internet

Atmospheric attenuation of millimeter and submillimeter waves : Models and computer code /

Atmospheric attenuation of millimeter and submillimeter waves is calculated for clear, fog, cloud and rain atmospheres. The frequency range considered is 1-1000 GHz. The clear atmospheres transmission spectra is calculated by a computer efficient algorithm of AFGL's HITRAN code. This new code is called FASCODE-1. The hydrometeor attenuation of fog, clouds and rain (precipitation), calculated by Mie scattering is addend to FASCODE-1. Models of fog, clouds and rain typical of mid-latitude temperate regions are used in calculations of transmission and attenuation.Research supported by the Air Force Geophysics Laboratory, Air Force Systems Command, United States Air Force, Hanscom AFB, Massachusetts.Optical Physics Division Project 7670.ADA084485 (from http://www.dtic.mil)."15 October 1979."Includes bibliographical references (pages 51-56).Atmospheric attenuation of millimeter and submillimeter waves is calculated for clear, fog, cloud and rain atmospheres. The frequency range considered is 1-1000 GHz. The clear atmospheres transmission spectra is calculated by a computer efficient algorithm of AFGL's HITRAN code. This new code is called FASCODE-1. The hydrometeor attenuation of fog, clouds and rain (precipitation), calculated by Mie scattering is addend to FASCODE-1. Models of fog, clouds and rain typical of mid-latitude temperate regions are used in calculations of transmission and attenuation.Mode of access: Internet

New Aerosol Models for the Retrieval of Aerosol Optical Thickness and Normalized Water-Leaving Radiances from the SeaWiFS and MODIS Sensors Over Coastal Regions and Open Oceans

We describe the development of a new suite of aerosol models for the retrieval of atmospheric and oceanic optical properties from the SeaWiFs and MODIS sensors, including aerosol optical thickness (tau), angstrom coefficient (alpha), and water-leaving radiance (L(sub w)). The new aerosol models are derived from Aerosol Robotic Network (AERONET) observations and have bimodal lognormal distributions that are narrower than previous models used by the Ocean Biology Processing Group. We analyzed AERONET data over open ocean and coastal regions and found that the seasonal variability in the modal radii, particularly in the coastal region, was related to the relative humidity, These findings were incorporated into the models by making the modal radii, as well as the refractive indices, explicitly dependent on relative humidity, From those findings, we constructed a new suite of aerosol models. We considered eight relative humidity values (30%, 50%, 70%, 75%, 80%, 85%, 90%. and 95%) and, for each relative humidity value, we constructed ten distributions by varying the fine-mode fraction from zero to 1. In all. 80 distributions (8Rh x 10 fine-mode fractions) were created to process the satellite data. We. also assumed that the coarse-mode particles were nonabsorbing (sea salt) and that all observed absorptions were entirely due to fine-mode particles. The composition of fine mode was varied to ensure that the new models exhibited the same spectral dependence of single scattering albedo as observed in the AERONET data

A wind dependent desert aerosol model: radiative properties /

This report presents a desert aerosol model that predicts aerosol radiative properties during background and severe dust storm conditions. The model treats the desert aerosol as an external mixture of natural carbon, water soluble and sand particles. The sand consists of two kinds of particles, pure quartz and quartz contaminated with a small amount of hematite. Mie calculations are performed using different size distributions and indices of refraction for each type of particle, and then a volume-weighting scheme is used to obtain the radiative properties of the aerosol as a whole. Attenuation coefficients, single scattering albedo and asymmetry parameter are given for 68 wavelengths between 0.2 and 300 micro. The results indicate that extinction is wavelength dependent for background conditions, but increases and becomes nearly constant for dust storm conditions. Indices of refraction, Desert aerosol, Aerosol modeling, Single scattering albedo, Radiative transfer, Optical properties.Research supported by the Air Force Geophysics Laboratory, United States Air Force, Hanscom AFB, Massachusetts.Performing organization : OptiMetrics, Inc., Burlington, Massachusetts."19 April 1988."Includes bibliographical references (pages 70-74).Appendix A. Aerosol fractions by volume as a function of wind speed -- Appendix B. Mie scattering calculations for the three components -- Appendix C. Radiative properties of the Desert Aerosol Model as a function of wind speed.This report presents a desert aerosol model that predicts aerosol radiative properties during background and severe dust storm conditions. The model treats the desert aerosol as an external mixture of natural carbon, water soluble and sand particles. The sand consists of two kinds of particles, pure quartz and quartz contaminated with a small amount of hematite. Mie calculations are performed using different size distributions and indices of refraction for each type of particle, and then a volume-weighting scheme is used to obtain the radiative properties of the aerosol as a whole. Attenuation coefficients, single scattering albedo and asymmetry parameter are given for 68 wavelengths between 0.2 and 300 micro. The results indicate that extinction is wavelength dependent for background conditions, but increases and becomes nearly constant for dust storm conditions. Indices of refraction, Desert aerosol, Aerosol modeling, Single scattering albedo, Radiative transfer, Optical properties.Mode of access: Internet

Comparison of 8 to 12 micrometer and 3 to 5 micrometer CVF transmissometer data with LOWTRAN calculations /

This report contains a description and analysis of a series of atmospheric transmittance measurements taken at the Targeting Systems Characterization Facility, Wright-Patterson Air Force Base, Ohio with a circular variable filter (CVF) transmissometer. The data cover the spectral regions from 8- to 12-micron and from 3- to 5-micron for both 8-km and 2.25-km atmospheric paths. The instrumentation is described and comparisons of the data with calculations using the atmospheric transmittance and background radiance code, LOWTRAN 6, are presented. Keywords include: Atmospheric transmittance; Atmospheric optics; Infrared; Attenuation; Absorption; and Aerosols.Optical Physics Division Project 7670, 2004."26 June 1984."Distributed to depository libraries in microfiche.Cover title.Includes bibliographical references (page 63).Scientific Interim.This report contains a description and analysis of a series of atmospheric transmittance measurements taken at the Targeting Systems Characterization Facility, Wright-Patterson Air Force Base, Ohio with a circular variable filter (CVF) transmissometer. The data cover the spectral regions from 8- to 12-micron and from 3- to 5-micron for both 8-km and 2.25-km atmospheric paths. The instrumentation is described and comparisons of the data with calculations using the atmospheric transmittance and background radiance code, LOWTRAN 6, are presented. Keywords include: Atmospheric transmittance; Atmospheric optics; Infrared; Attenuation; Absorption; and Aerosols.Mode of access: Internet