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Mike Pavolonis (NOAA/NESDIS/STAR)

Preliminary Assessment of Eyjafjallajokull Ash Heights Retrieved from SEVIRI and MODIS on May 6 - 7, 2010. Mike Pavolonis (NOAA/NESDIS/STAR). Overview.

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Mike Pavolonis (NOAA/NESDIS/STAR)

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  1. Preliminary Assessment of Eyjafjallajokull Ash Heights Retrieved from SEVIRI and MODIS on May 6 - 7, 2010 Mike Pavolonis (NOAA/NESDIS/STAR)

  2. Overview • Spaceborne lidar observations from CALIPSO were used to assess the accuracy of the infrared ash height retrievals performed using SEVIRI and MODIS on May 6 - 7, 2010 over the Atlantic Ocean. • The infrared retrieval algorithm used to determine ash cloud height accounts for transmission of radiation through semi-transparent ash clouds (e.g. the cloud is NOT assumed to be a blackbody). • The SEVIRI measurements were NOT corrected for parallax, which may slightly impact the comparisons (especially for CASE #2). • Special thanks to the CALIPSO Team at NASA Langley for providing expedited L1 data. • The lidar total attenuated backscatter has a vertical resolution of 60 m, which allows for a high quality depiction of the ash cloud top.

  3. CASE #1: May 6, 2010 (13:45 UTC) Aqua MODIS End of CALIOP cross section Met-9 SEVIRI Start of CALIOP cross section Ash and ice clouds Ash cloud overlapping liquid water cloud CALIOP 532 nm total attenuated backscatter

  4. White circles: MODIS ash height retrievals Aqua MODIS CASE #1: May 6, 2010 (13:45 UTC) White circles: SEVIRI ash height retrievals Magenta circles: 11 m brightness temperature inferred height Met-9 SEVIRI

  5. CASE #2: May 7, 2010 (03:15 UTC) Ireland Aqua MODIS Startof CALIOP cross section Met-9 SEVIRI End of CALIOP cross section Ash clouds overlapping boundary layer cloud CALIOP 532 nm total attenuated backscatter

  6. White circles: MODIS ash height retrievals Aqua MODIS CASE #2: May 7, 2010 (03:15 UTC) Magenta circles: 11 m brightness temperature inferred height White circles: SEVIRI ash height retrievals Met-9 SEVIRI

  7. CASE #3: May 7, 2010 (14:25 UTC) Aqua MODIS Endof CALIOP cross section Met-9 SEVIRI Start of CALIOP cross section Ash clouds overlapping boundary layer cloud CALIOP 532 nm total attenuated backscatter

  8. White circles: MODIS ash height retrievals Aqua MODIS CASE #3: May 7, 2010 (14:25 UTC) White circles: SEVIRI ash height retrievals Magenta circles: 11 m brightness temperature inferred height Met-9 SEVIRI

  9. Conclusions • The retrieval algorithm used to determine ash cloud height accounts for transmission of radiation through semi-transparent ash clouds (e.g. the cloud is NOT assumed to be a blackbody). This is critical since all of the ash clouds observed by CALIOP were semi-transparent to infrared radiation. • With the exception of cloud edges, the ash heights retrieved using multi-spectral infrared measurements from SEVIRI and MODIS are in good agreement with spaceborne lidar measurements (generally within 3 km). • The larger view angles associated with the SEVIRI measurements allow for better ash detection and ash height retrievals (e.g. higher signal to noise). Gu et al. (2005) also showed that the longer path length through the ash clouds increases sensitivity. • Boundary layer stratus cloud decks beneath the ash clouds are likely influencing the retrievals to some degree (especially in Case #3). • All of the ash clouds observed by CALIOP were semi-transparent, thus 11 m brightness temperature inferred cloud heights have a severe low bias. • A more quantitative assessment will be performed when the CALIPSO cloud layers data product is released for these dates.

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