Professor Roy Grainger

Abstract:

Two years (January 1999 - January 2001) of data from the Along-Track Scanning Radiometer 2 (ATSR-2) aboard the satellite ERS-2 have been processed with an automatic ship track detection algorithm. The distribution of detected tracks shows similar patterns and magnitudes to another satellite-derived dataset and is consistent with locations of shipping lanes. Most tracks are detected in the North Pacific and North Atlantic, between March and August. The derived track masks have been used with ATSR-2 data from the Oxford-RAL Aerosol and Clouds (ORAC) retrieval scheme to reveal differences between track and non-track clouds. Water clouds which are part of a ship track show an approximate 50% increase in optical depth as compared to background cloud conditions (30 km or more from tracks), and a decrease in effective radius of similar magnitude. This is consistent with the first aerosol indirect (Twomey) effect.

Abstract:

Traditionally the atmospheric physics department at the University of Oxford has applied optimal estimation techniques for the retrieval of atmospheric properties of gases; temperature, pressure and volume mixing ratio from satellite measurements. This paper describes the latest novel application of these techniques in deriving aerosol optical properties in laboratory experiments. Two examples are given; a spectral resolved technique allows an aerosol refractive index to be derived over a wide wavelength range and a method of deriving single particle refractive index and size from a novel aerosol instrument suitable for in situ aerosol monitoring.

Abstract:

The effect of wind speed on aerosol optical depth (AOD) at 0.55 μm over remote ocean regions is investigated. Remote ocean regions are defined by the combination of AOD from satellite observation and wind direction from ECMWF. According to our definition, many ocean regions cannot be taken as remote ocean regions due to long-range transportation of aerosol from continents. Highly correlated linear relationships are found in remote ocean regions with a wind speed range of 0-20 ms-1. The enhancement of AOD at high wind speed is explained as the increase of sea salt aerosol production. © 2010 Author(s).

Abstract:

The Global Retrieval of ATSR Cloud Parameters and Evaluation (GRAPE) project has produced a global data-set of cloud and aerosol properties from the Along Track Scanning Radiometer-2 (ATSR-2) instrument, covering the time period 1995-2001. This paper presents the validation of aerosol optical depths (AODs) over the ocean from this product against AERONET sun-photometer measurements, as well as a comparison to the Advanced Very High Resolution Radiometer (AVHRR) optical depth product produced by the Global Aerosol Climatology Project (GACP).

The GRAPE AOD over ocean is found to be in good agreement with AERONET measurements, with a Pearson's correlation coefficient of 0.79 and a best-fit slope of 1.0 ± 0.1, but with a positive bias of 0.08 ± 0.04. Although the GRAPE and GACP datasets show reasonable agreement, there are significant differences. These discrepancies are explored, and suggest that the downward trend in AOD reported by GACP may arise from changes in sampling due to the orbital drift of the AVHRR instruments. © Author(s) 2010.