Norman Kuring

Asian dust events of April 1998

On April 15 and 19, 1998, two intense dust storms were generated over the Gobi desert by springtime low-pressure systems descending from the northwest. The windblown dust was detected and its evolution followed by its yellow color on SeaWiFS satellite images, routine surface-based monitoring, and through serendipitous observations. The April 15 dust cloud was recirculating, and it was removed by a precipitating weather system over east Asia. The April 19 dust cloud crossed the Pacific Ocean in 5 days, subsided to the surface along the mountain ranges between British Columbia and California, and impacted severely the optical and the concentration environments of the region. In east Asia the dust clouds increased the albedo over the cloudless ocean and land by up to 10–20%, but it reduced the near-UV cloud reflectance, causing a yellow coloration of all surfaces. The yellow colored backscattering by the dust eludes a plausible explanation using simple Mie theory with constant refractive index. Over the West Coast the dust layer has increased the spectrally uniform optical depth to about 0.4, reduced the direct solar radiation by 30–40%, doubled the diffuse radiation, and caused a whitish discoloration of the blue sky. On April 29 the average excess surface-level dust aerosol concentration over the valleys of the West Coast was about 20–50 μg/m3 with local peaks >100 μg/m3. The dust mass mean diameter was 2–3 μm, and the dust chemical fingerprints were evident throughout the West Coast and extended to Minnesota. The April 1998 dust event has impacted the surface aerosol concentration 2–4 times more than any other dust event since 1988. The dust events were observed and interpreted by an ad hoc international web-based virtual community. It would be useful to set up a community-supported web-based infrastructure to monitor the global aerosol pattern for such extreme aerosol events, to alert and to inform the interested communities, and to facilitate collaborative analysis for improved air quality and disaster management.

Ocean color: Availability of the global data set

The National Aeronautics and Space Administration/ Goddard Space Flight Centers Nimbus Project Office, in collaboration with the NASA/GSFC Space Data and Computing Division, the NASA/GSFC Laboratory for Oceans and the University of Miami/Rosenstiel School of Marine and Atmospheric Science, have undertaken to process all data acquired by the Coastal Zone Color Scanner (CZCS) to Earth-gridded geophysical values and to provide ready access to data products [Esaias et al., 1986]. An end-to-end data system utilizing recent advances in data base management and both digital and analog optical disc storage technologies has been developed to handle the processing, analysis, quality control, archiving and distribution of this data set. A more complete description of this system, which has been fully operational for the past 2 years, is in preparation. The entire Level-1 data set (see Tables 1, 2) has been copied from magnetic tape to digital optical disc, and all data from the first 32 months (50% of the total scenes acquired, and covering the period November 1978 through June 1981) have been processed to Levels 2 and 3 and are now available for distribution. The remainder of the data set should be completed and released by fall 1989.

Ocean color measurements with the Operational Land Imager on Landsat-8: implementation and evaluation in SeaDAS

Abstract. The Operational Land Imager (OLI) is a multispectral radiometer hosted on the recently launched Landsat8 satellite. OLI includes a suite of relatively narrow spectral bands at 30 m spatial resolution in the visible to shortwave infrared, which makes it a potential tool for ocean color radiometry: measurement of the reflected spectral radiance upwelling from beneath the ocean surface that carries information on the biogeochemical constituents of the upper ocean euphotic zone. To evaluate the potential of OLI to measure ocean color, processing support was implemented in Sea-viewing Wide Field-of-View Sensor (SeaWiFS) Data Analysis System (SeaDAS), which is an open-source software package distributed by NASA for processing, analysis, and display of ocean remote sensing measurements from a variety of spaceborne multispectral radiometers. Here we describe the implementation of OLI processing capabilities within SeaDAS, including support for various methods of atmospheric correction to remove the effects of atmospheric scattering and absorption and retrieve the spectral remote sensing reflectance (Rrs; sr−1). The quality of the retrieved Rrs imagery will be assessed, as will the derived water column constituents, such as the concentration of the phytoplankton pigment chlorophyll a.

Satellite-derived estimates of primary production on the northwest Atlantic continental shelf

Abstract Synoptic estimation of rates of primary production from remote observation of ocean color is essential for determination of the oceans role in global carbon cycles. Models having a physiological and optical basis have been developed to predict water-column primary production, normalized to water-column biomass, as a linear function of sea-surface irradiance. Such a model is applied using 41 successive images of sea-surface chlorophyll concentration derived from the Coastal Zone Color Scanner (CZCS) and covering the northeast coast of the U.S. and Canada in the spring of 1979. The CZCS level III data set for the northwest Atlantic continental shelf includes estimates of surface chlorophyll concentration and percent cloud cover on a 10 km grid. Linear regression techniques are used to calibrate the CZCS chlorophyll estimates with ship measurements and to convert percent cloud cover into sea-surface irradiance; such satellite-derived irradiance estimates are significant predictors of irradiances recorded at the earths surface. The satellite-derived primary production values have been composited as monthly images. The enhanced production of the spring bloom is evident in areas corresponding to major fisheries such as Georges Bank and offshore Yarmouth, Nova Scotia, while the lower production in the Gulf Stream and an associated warm-core ring can be seen farther to the south. Bottom topography seems to have a major influence on rates of primary production, particularly in waters shallower than 100 m. The relative error estimated for these calculations of primary production is approximately 75%.