A critical look at spatial scale choices in satellite-based aerosol indirect effect studies
Analysing satellite datasets over large regions may introduce spurious relationships between aerosol and cloud properties due to spatial variations in aerosol type, cloud regime and synoptic regime climatologies. Using MODerate resolution Imaging Spectroradiometer data, we calculate relationships be...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2010-12-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/10/11459/2010/acp-10-11459-2010.pdf |
| Summary: | Analysing satellite datasets over large regions may introduce spurious
relationships between aerosol and cloud properties due to spatial variations
in aerosol type, cloud regime and synoptic regime climatologies. Using
MODerate resolution Imaging Spectroradiometer data, we calculate
relationships between aerosol optical depth τ<sub>a</sub> derived liquid
cloud droplet effective number concentration <i>N</i><sub>e</sub> and liquid cloud
droplet effective radius <i>r</i><sub>e</sub> at different spatial scales. Generally,
positive values of <span style="border-bottom: 1px solid #000; vertical-align: 50%;
font-size: 10px; color: #000;">dln<i>N</i><sub>e</sub></span><span style="margin-left: -3em;
margin-right: .5em; vertical-align: -15%; font-size: 10px; color:
#000;">dlnτ<sub>a</sub></span> are found for ocean regions, whilst negative values occur for many land
regions. The spatial distribution of <span style="border-bottom: 1px solid #000; vertical-align: 50%;
font-size: 10px; color: #000;">dln<i>r</i><sub>e</sub></span><span style="margin-left: -2.7em;
margin-right: .5em; vertical-align: -15%; font-size: 10px; color:
#000;">dlnτ<sub>a</sub></span> shows approximately the opposite pattern, with
generally postive values for land regions and negative values for ocean
regions. We find that for region sizes larger than
4° × 4°, spurious spatial variations in retrieved
cloud and aerosol properties can introduce widespread significant errors to
calculations of <span style="border-bottom: 1px solid #000; vertical-align: 50%;
font-size: 10px; color: #000;">dln<i>N</i><sub>e</sub></span><span style="margin-left: -3em;
margin-right: .5em; vertical-align: -15%; font-size: 10px; color:
#000;">dlnτ<sub>a</sub></span> and <span style="border-bottom: 1px solid #000; vertical-align: 50%;
font-size: 10px; color: #000;">dln<i>r</i><sub>e</sub></span><span style="margin-left: -2.7em;
margin-right: .5em; vertical-align: -15%; font-size: 10px; color:
#000;">dlnτ<sub>a</sub></span>. For regions on the
scale of 60° × 60°, these methodological errors may
lead to an overestimate in global cloud albedo effect radiative forcing of
order 80% relative to that calculated for regions on the scale of 1° × 1°. |
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| ISSN: | 1680-7316 1680-7324 |