1. S-HIS Retrieval Study Sahara Air Layer (SAL) Caribbean Sea: 19 July 2007 TC4 Robert Knuteson and S-HIS team Uni. Of Wisconsin-Madison Space Science and Engineering Center Updated: 21 August 2007

2. Topics Background Retrieval Method CIMSS SAL Image 19 July 2007 Flight Track NASA Cloud Physics Lidar (CPL) Recursive Quicklook retrieval Recursive Iterative retrieval Tendency Relative to 15:00 UTC Conclusions

3. Background NASA TC4 mission (Tropical Composition, Cloud and Climate Coupling) GOES monitors Sahara Air Layer (SAL) airmass moving across Atlantic. GOES SAL remnant observed on 19 July 2007 in Western Caribbean. ER-2 & DC-8 mission is planned to fly across the Caribbean (SW to NE) from San Jose, CR. ER-2 flies on 19 th July and DC-8 on the 20 th. NASA Cloud Physics Lidar (CPL) on the ER-2 detects a thick aerosol layer in the Western Caribbean which becomes shallower in Eastern Caribbean. UW-Madison Scanning-HIS instrument on the ER-2 measures upwelling infrared radiance spectrum across the Caribbean and on the return leg. A UW-Madison physical retrieval method was used to derive the atmospheric temperature, water vapor, and ozone profiles below the aircraft.

4. S-HIS Physical Retrieval Method A physical iterative retrieval method was implemented to simultaneously solve for atmospheric temperature, water vapor, ozone profiles and skin temperature from the Scanning-HIS upwelling radiances (Antonelli). The retrieval uses the Bayesian optimal estimation technique known as the Maximum A Posteriori (MAP) method (Rodgers). A line-by-line forward model (AER LBLRTM v10.3+) was used to minimize the observed minus calculated radiances along with analytic jacobians (Clough). The a priori climatology was create at UW-CIMSS from a multi-year set of radiosonde observations augmented with ozone profiles (Woolf). The domain of the climatology (approx. 6000 profiles) is shown below. The Newton-Gauss method was implemented to find the zero of the derivative of the joint probability distribution (pdf) corresponding to the optimal solution. The actual form used is x = x a +(K T S e -1 K+S a -1 ) -1 K T S e -1 *[R-F(x)+ K*(x-x a )] R is the observation, F(x) the forward model, K is the jacobian dF/dx, and S is the covariance where “a” refers to the a priori climatology and “e” to the measurement error covariance.

5. http://cimss.ssec.wisc.edu/tropic2/real-time/salmain.php?&prod=splitEW&time GOES detection of Sahara Air Layer (SAL) A collaboration between the UW/NOAA/NASA Cooperative Institute for Meteorological Satellite Studies (CIMSS) and the NOAA Hurricane Research Division (HRD) has identified a real-time method using geostationary weather satellites to monitor the dry air masses that travel from North Africa westward across the Atlantic (Velden/Dunion). SAL Detected by GOES In Western Caribbean 19 July 2007 15:00 UTC

6. GOES SAL NASA TC4 ER-2 Mission: 19 July 2007 Real-Time Mission Monitor: 17:00 UTC GOES IR4 The NASA ER-2 flew at 20 km altitude over the SAL detected by GOES in the western Caribbean and then returned along a nearby track. [http://rtmm.nsstc.nasa.gov/index.html]

7. NASA CPL 19 July 2007 14:55 to 16:25 UTC Within GOES detected SAL Exiting GOES SAL to the East East of GOES SAL

8. NASA CPL 19 July 2007 16:25 to 17:55 UTC East of GOES detected SAL Entering GOES SAL to the West Within GOES SAL

9. S-HIS Recursive Single Iteration Retrieval: 15-18 UTC (quicklook mode) Relative Humidity Indicates Elevated Dry Layer Cloud Effects Otherwise Temperature Fairly Uniform RH T West to East East to West

10. Title Clouds Distort The Vertical Profile In the Single Iteration Retrieval West to East East to West

11. S-HIS Recursive Full Iterative Retrieval : 15-18 UTC Elevated Dry Layer Eastern Caribbean Convergence Test Removes Cloud Effects RH T Deep Dry Layer In Western Caribbean West to East East to West

12. Effect of Iteration on Convergence Sharpens Dry Layer Boundaries Increases Temperature at base of Dry Layer RH T

13. Independent First Guess – Climatology (Full Iterative Retrieval : 15-16.5 UTC) Elevation Of Dry Layer Outbound Leg Only RH T

14. Recursive minus Independent First Guess ( Full Iterative Retrieval : 15-16.5 UTC) dRH dT dRH < ±5 % dT < ±0.1 K Good Agreement

15. Retrieval Tendency - Recursive Iterative Retrieval : 15-18 UTC Warming At base Of Dry Layer Elevation Of Dry Layer RH T Symmetrical about aircraft turnaround at 16:30 UTC

16. SAL Retrieval Study Conclusions: An ER-2 mission during the TC4 campaign was devoted to the study of the remnant of a Sahara Air Layer in the Caribbean on 19 July 2007. The GOES infrared split-window indicates the presence of the SAL in the western Caribbean Sea but not in the eastern portion. The NASA Cloud Physics Lidar on the ER-2 measured a thick aerosol layer between the surface and 5 km in the western Caribbean and a shallower layer (0-3 km) in the eastern Caribbean. The UW Scanning-HIS retrievals of temperature and water vapor show a deep dry layer (low relative humidity) just above the marine boundary layer (1 to 8 km) in the western Caribbean in the GOES indicated SAL region. The S- HIS retrievals show that the lower boundary of the dry layer elevates to about 4 km in the eastern Caribbean outside the GOES SAL region with a moist layer below. The UW S-HIS retrieval of temperature suggests a warming at the base of the dry layer. Is this related to aerosol heating from solar absorption? The convective stability deduced from the S-HIS profiles suggests …(tbd) This study suggests that the infrared advanced sounder on a Geostationary platform could provide much needed thermodynamic profile data of the Sahara Air Layer and it’s role in suppression of hurricane activity.