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Marine Boundary Layer Cloud-top Altitude Analysis From Satellite Measurements

Marine Boundary Layer Cloud-top Altitude Analysis From Satellite Measurements. Mary Jordan Phil Durkee Department of Meteorology Naval Postgraduate School Research Sponsor: SPAWAR. BACIMO 2003 Conference Monterey, CA 9-11 September 2003. SEMEO Project.

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Marine Boundary Layer Cloud-top Altitude Analysis From Satellite Measurements

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  1. Marine Boundary Layer Cloud-top Altitude Analysis From Satellite Measurements Mary Jordan Phil Durkee Department of Meteorology Naval Postgraduate School Research Sponsor: SPAWAR BACIMO 2003 Conference Monterey, CA 9-11 September 2003

  2. SEMEO Project • Estimation of marine cloud-top height is one element of the project Satellite-Derived Marine Atmospheric Boundary Layer and EM/EO Properties (SEMEO). • SEMEO Purpose: to estimate the location and strength of elevated ducts in coastal and open ocean regions. • Marine stratus unobscured by upper level clouds • The cloud-top height is the Optimum Coupling Height (OCH) for an elevated duct (Helvey, 2000). • Technique is applied to NPOES and GOES satellites

  3. NPS Cloud-Top Height Algorithm • The cloud-top height algorithm used in SEMEO was developed in the MS Thesis of LT Blake McBride, USN (June 2000). • Inputs: • IR cloud-top temperature (11 micron, Channel 4) • Surface Temperature

  4. NPS Cloud-Top Height Algorithm • Assumptions: • Constant vertical cloud fraction in the boundary layer • Vertical cloud fraction is related to cloud-top height. • Deep boundary layers (> 400 m): top 1/3 is cloud • Shallow boundary layers (< 400 m): top 2/3 is cloud • Use dry adiabatic lapse rate to estimate depth of cloud-free boundary layer. • Use moist adiabatic lapse rate to estimate depth of clouds in boundary layer.

  5. Strong Subsidence Pseudo-Adiabatic Lapse Rate Dry Adiabatic Lapse Rate TS DT = TCT - TS TCT Inversion Marine Stratocumulus LCL Ocean

  6. Validation Cases • FIRE (1987): 9 cases • Rawinsonde • Measured SST • NPOES • MAST (1994): 15 cases • Rawinsonde • Measured SST or Air Temperature • NPOES • CARMA (2002): 29 cases • Aircraft profile • NAVO "K10" SST Field • 0.1 degree resolution • NPOES and GOES

  7. GOES-10 1915 UTC 28 August 2002

  8. NAVO Sea-Surface Temperature28 August 2002

  9. Comparison Measured vs. Estimated28 August 2002 Cloud Top Cloud Base

  10. Verification Statistics RMS Difference Fire: 66.2 m Mast: 108.6 m Carma: 81.8 m All Cases:88.0 m

  11. GOES-10 1930 UTC 31 August 2002

  12. NAVO Sea-Surface Temperature31 August 2002

  13. Comparison Measured vs. Estimated31 August 2002 Cloud Top Cloud Base • Warm SST under the cloud is not representative of the surface air temperature which generated the cloud. • Possible explanations: • SST field is inaccurate. • Boundary layer developed along a trajectory that crosses a strong SST gradient (from cold to warm)

  14. SEMEO Automation Process Map 11-km SST field to AVHRR or GOES domains (1 km or 4 km) Identify Low Cloud Area in 1-km AVHRR or 4-km GOES; output field is Cloud-Top Temperature Add Estimates of Refractivity Profile to Height Field Compute Cloud-Top Height on 1-km or 4-km domain

  15. Summary & Future • 88 meter RMS height difference for 53 cases is promising. • These cases were chosen to show algorithm performance under the best conditions. • There was good agreement between NPOES and GOES height estimates on each day (not shown). • Improve the surface temperature estimate. • Use back trajectory to compute a weighted average of the SST • Should improve results in vicinity of SST gradients • Validate with additional existing cases.

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