Comparison of cloud properties observed from in situ and satellite measurements
Abstract
Climate is influenced by clouds reflecting radiation. Adjustments in cloud properties occur with changes to the cloud environment such as changes in aerosol or vertical velocity. These adjustments change the cloud radiative forcing. Three ways exist to study cloud properties: in situ observations, satellite observations, and modeling of cloud properties. Data sets from in situ measurements in field campaigns such as Physics of Stratocumulus Top (POST) (Hudson et al. 2010; Hudson and Noble 2013) provide good resolution of local cloud properties but are not extensive over time or globally. Satellites provide data coverage on a global scale and over long times but at infrequent periods locally. Uncertainties arise between these two methods when attempting to understand cloud properties and effects on radiative forcing. To understand these uncertainties, we compared MODIS data to vertical cloud pass data from the POST field campaign. Data from 9 in situ slant passes were compared to data from 9 satellite passes on 8 days. Figure 1 shows these comparisons of effective radius (re) (black) and cloud optical depth (COD) (red). COD from the satellite passes compares well with in situ data near the 1:1 line. The correlation coefficient (R) for COD is 0.95 with a slope (k) of 1.05. However, re is not near the 1:1 line and shows a steep k of 2.36, which suggests an over-prediction by the satellite observations, while R is only 0.57. Satellite re compared better to maximum in situ re which yielded a flatter k of 1.44 but an R of 0.59. Maximum re occurred a few meters below stratus cloud top that may suggest larger droplets dominate over cloud thickness in satellite observations. The satellite also over-predicts liquid water path (LWP, not shown) with a k of 1.42 and an R of 0.90. Because satellite re is over-predicting, calculations of environmental precursors become more difficult. However, COD is more related to albedo and observations compare well, which appears to validate climate change calculations involving satellite COD. Hudson, J. G. and S. Noble (2013), accepted J. Atmos. Sci.. Hudson, J. G., S. Noble, and V. Jha (2010), Geophys. Res. Lett., 37, L21813. Figure 1. Satellite effective radius (re) (black) and cloud optical depth (COD) (red) compared with re and COD calculated from measurements taken from in situ vertical slant passes through the cloud.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.A41C0064N
- Keywords:
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- 0320 ATMOSPHERIC COMPOSITION AND STRUCTURE Cloud physics and chemistry;
- 0321 ATMOSPHERIC COMPOSITION AND STRUCTURE Cloud/radiation interaction