Larry L. Stowe

Characterization of tropospheric aerosols over the oceans with the NOAA advanced very high resolution radiometer optical thickness operational product

The National Oceanic and Atmospheric Administration (NOAA) advanced very high resolution radiometer (AVHRR) is an instrument on a polar orbiting satellite that provides information on global aerosol distributions. The remote sensing algorithm is based on measurements of backscattered solar radiation which yield a measure of the radiatively equivalent aerosol optical thickness τ A sat (EAOT) over the oceans. Seasonally composited EAOT data for the period July 1989 to June 1991 reveal many spatially coherent plume-like patterns that can usually be interpreted in terms of known (or reasonably hypothesized) sources in association with climatological wind fields. The largest and most persistent areas of high EAOT values are associated with wind-blown dust and biomass burning sources; especially prominent are sources in Africa, the middle East, and the Asian subcontinent. Prominent plumes over the midlatitude North Atlantic are attributed to pollution emissions from North America and Europe. Large plumes attributed to pollution aerosols and dust from sources in Asia are clearly visible over the western and central North Pacific. On a global scale the annually averaged northern hemisphere EAOT values are about 1.7 times greater than those in the southern hemisphere. Considering each hemisphere separately, EAOT values in summer are about twice those in winter. Within the midlatitude band 30°-60° (i.e., where anthropogenic emissions are greatest) the summer/winter ratio is about 3. The temporal variability of monthly mean EAOT in specific ocean regions often shows characteristic seasonal patterns that are usually consistent with aerosol measurements made in the marine boundary layer. Nonetheless, there are features in the EAOT distributions that can not be readily interpreted at this time. The AVHRR EAOT distributions demonstrate that satellite products can serve as a useful tool for the planning and implementation of focused aerosol research programs and that they will be especially important in studies of climate-related processes.

Development, validation, and potential enhancements to the second‐generation operational aerosol product at the National Environmental Satellite, Data, and Information Service of the National Oceanic and Atmospheric Administration

A revised (phase 2) single-channel algorithm for aerosol optical thickness, τSATA, retrieval over oceans from radiances in channel 1 (0.63 μm) of the advanced very high resolution radiometer (AVHRR) has been implemented at the National Oceanic and Atmospheric Administrations National Environmental Satellite Data and Information Service for the NOAA 14 satellite launched December 30, 1994. It is based on careful validation of its operational predecessor (phase 1 algorithm), implemented for NOAA 11 in 1989. Both algorithms scale the upward satellite radiances in cloud-free conditions to aerosol optical thickness using an updated radiative transfer model of the ocean and atmosphere. Application of the phase 2 algorithm to three matchup Sun-photometer and satellite data sets, one with NOAA 9 in 1988 and two with NOAA 11 in 1989 and 1991, respectively, show systematic error is less than 10%, with a random error of στ≈0.04. First results of τSATA retrievals from NOAA 14 using the phase 2 algorithm, and from checking its internal consistency, are presented. The potential two-channel (phase 3) algorithm for the retrieval of an aerosol size parameter, such as the Junge size distribution exponent, by adding either channel 2 (0.83 μm) from the current AVHRR instrument, or a 1.6-μm channel to be available on the Tropical Rainfall Measurement Mission and the NOAA-KLM satellites by 1997 is under investigation. The possibility of using this additional information in the retrieval of a more accurate estimate of aerosol optical thickness is being explored.

Aerosol properties and radiative effects in the United States East Coast haze plume: An overview of the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX)

Aerosol effects on atmospheric radiation are a leading source of uncertainty in predicting climate change. The Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) was designed to reduce this uncertainty by measuring and analyzing aerosol properties and effects on the United States eastern seaboard, where one of the worlds major plumes of urban/industrial haze moves from the continent over the Atlantic Ocean. The TARFOX intensive field campaign was conducted July 10–31, 1996. It included coordinated measurements from four satellites (GOES-8, NOAA-14, ERS-2, Landsat), four aircraft (ER-2, C-130, C-131A, and a modified Cessna), land sites, and ships. A variety of aerosol conditions was sampled, ranging from relatively clean, behind frontal passages, to moderately polluted, with aerosol optical depths exceeding 0.5 at midvisible wavelengths. Gradients of aerosol optical thickness were sampled to aid in separating aerosol effects from other radiative effects and to more tightly constrain closure tests, including those of satellite retrievals. Early results from TARFOX include demonstration of the unexpected importance of carbonaceous compounds and water condensed on aerosol in the United States East Coast haze plume, chemical apportionment of the aerosol optical depth, measurements of aerosol-induced changes in upwelling and downwelling shortwave radiative fluxes, and generally good agreement between measured flux changes and those calculated from measured aerosol properties. This overview presents the TARFOX objectives, rationale, overall experimental approach, and key initial findings as a guide to the more complete results reported in this special section and elsewhere.

Monitoring the Mt. Pinatubo aerosol layer with NOAA/11 AVHRR data

The NOAA/NESDIS operational aerosol optical thickness product has provided an exceptional view of the development of the Mt. Pinatubo stratospheric aerosol layer. The product is derived from reflected solar radiation measurements of the Advanced Very High Resolution Radiometer onboard the NOAA/11 polar orbiting environmental satellite. The greater the optical thickness, the greater the amount of reflected solar radiation. Daily and weekly composites of aerosol optical thickness (AOT) at a wavelength of 0.5 micrometers have been analyzed to monitor the spatial and temporal variability of the aerosol layer and its optical thickness since the major eruption of Mt. Pinatubo on June 15, 1991. These analyses show that: the volcanic aerosol layer circled the Earth in 21 days; there are inhomogeneities in the layer that seem to remain after over two months of circling the Earth; using an AOT of 0.1 to define the layer, it covered about 42% of the Earths surface area after two months, over twice the area covered by the El Chichon aerosol layer two months after its eruption; the layer is confined to the latitude zone 20S to 30N, with occasional patches seen at somewhat higher latitudes; the largest mean optical thickness of the layer was 0.31, occurring on August 23rd; the mass of SO2 required to produce this aerosol optical thickness is 13.6 megatons; and, the globally averaged net radiation at the top of the atmosphere may be reduced by about 2.5 Wm−2 (cooling effect of at least 0.5°C) once the aerosol is distributed globally over the next two to four years.

Scientific Basis and Initial Evaluation of the CLAVR-1 Global Clear/Cloud Classification Algorithm for the Advanced Very High Resolution Radiometer

This invention is addressed to an improved method for the recovery of alkali metal salts of caphalothin from aqueous solution in which a non-toxic alkali metal salt is added in the aqueous solution to precipitate the cephalothin salts substantially free of impurities.

Global distribution of cloud cover derived from NOAA/AVHRR operational satellite data

Abstract NOAA/NESDIS is developing an algorithm for the remote sensing of global cloud cover using multi-spectral radiance measurements from the Advanced Very High Resolution Radiometer (AVHRR) on-board NOAA polar orbiting satellites. The current (Phase 1) algorithm uses a sequence of “universal” threshold tests to classify all 2×2 pixel arrays of GAC (4 km) observations into clear, mixed and cloudy categories. A subsequent version of the algorithm (Phase II) will analyze the previous 9-day series of mapped ( 1 2 degree) “clear” array data to replace the “universal” thresholds with space and time specific values. This will provide more accurate estimates of cloud amount for each pixel. The current algorithm is being implemented into the operational data processing stream for testing and evaluation of experimental products. Eventually, it is intended for use operationally to support weather and climate diagnosis and forecasting programs, as well as to provide clear sky radiance data sets for other remote sensing parameters, e.g., vegetation index, aerosol optical thickness, and sea surface temperature.

Remote sensing of aerosols over the oceans using AVHRR data Theory, practice and applications

Abstract The basic features of single- and dual-channel aerosol retrieval algorithms based on matching radiances measured in AVHRR channels -1 (∼0.58-0.68 μm) and -2( ∼0.73-1.10μm) with model computations will be described. The use of the NOAA/NESDIS single-channel algorithm will be illustrated with examples of detection and mapping of enhanced atmospheric turbidity over the oceans. The effects of variations in the physical and radiative properties of atmospheric aerosols, and in atmospheric ozone and water vapour, will be briefly discussed in the light of model sensitivity analyses.

Aerosol Retrievals from Individual AVHRR Channels. Part I: Retrieval Algorithm and Transition from Dave to 6S Radiative Transfer Model

Abstract The present second-generation aerosol retrieval algorithm over oceans used at NOAA/National Environmental Satellite, Data, and Information Service (NESDIS) separately retrieves two values of aerosol optical depth, τ1 and τ2, from Advanced Very High Resolution Radiometer (AVHRR) channels 1 and 2 centered at λ1 = 0.63 (operational) and λ2 = 0.83 μm (experimental), respectively. From these, an effective Angstrom exponent α, related to particle size, can be derived as α = −ln(τ1/τ2)/ln(λ1/λ2). The single-channel lookup tables, relating reflectance to optical depth in the retrievals, have been precalculated with the Dave (1973) scalar radiative transfer (RT) model. This first part of a two-part paper describes the retrieval algorithm, with emphasis on its RT modeling related elements, and documents the transition to the Second Simulation of the Satellite Signal in the Solar Spectrum (6S; 1997) RT model. The new 6S RT model has the capability to account for reflection from wind-roughened sea surface, o...

Use of volcanic aerosols to study the tropical stratospheric reservoir

Aerosol data obtained by the advanced very high resolution radiometer on NOAA 11, the improved stratospheric and mesospheric sounder on the upper atmospheric research satellite, one airborne lidar system, and several ground-based lidar systems up to 2-1/2 years after the eruption of Mount Pinatubo are used to study stratospheric dynamics. In particular, this study focuses on the tropical stratospheric reservoir and transport from it to northern midlatitudes following the eruption of Mount Pinatubo. This includes: The build-up and removal rates for sulfate aerosol, the position and motion of the center of the reservoir, and the position and width of its boundaries at altitudes of the volcanic aerosols. Ozone data from the total ozone mapping spectrometer were also used to study the position and width of the reservoir boundaries. In addition, ground-based lidar stratospheric aerosol data are used to study aerosol transport from the reservoir to the northern hemisphere as it relates to winds in the tropical stratosphere. Finally, historical in situ and satellite data were used to examine how the time and location of volcanic injections into the stratosphere affect the aerosol decay rates and seasonal variations of aerosol optical depth in the midlatitude stratosphere.

Validation of the NOAA/NESDIS satellite aerosol product over the North Atlantic in 1989

A validation experiment and resulting potential improvements to the operational satellite aerosol optical thickness product at the National Oceanic and Atmospheric Administration/National Environmental Satellite Data and Information Service (NOAA/NESDIS) are presented. An earlier paper described a set of Sun photometer measurements collected from the Soviet R/V Akademik Vernadsky during its cruise in the Atlantic Ocean and Mediterranean Sea from September to December 1989. The accuracy of the Sun photometer aerosol optical thickness was proven acceptable for use as a ground truth standard for validation of the NOAA product. This paper describes the validation methodology and the results of its application to the NOAA 11 satellite product. A systematic underestimation in the operational values by about 35%, relative to the ship truth, is found. Causes for this discrepancy are examined, emphasizing the importance of careful satellite instrument calibration, and a revision of the oceanic reflectance model used in the retrieval algorithm. It is shown that the remaining systematic underestimate in satellite aerosol optical thickness can be attributed only to the aerosol model used in the retrieval. Additional checks of this conclusion using independent data sets are underway. If confirmed, a fundamental revision of the presently used aerosol model would be required. An example of a simple adjustment to the present aerosol model which successfully removes the bias is given, based on the assumption of an absorbing aerosol.