1. Atmospheric profile and precipitation properties derived from radar and radiosondes during RICO Louise Nuijens With thanks to: Bjorn Stevens (UCLA) Margreet van Zanten & Pier Siebesma (KNMI) September 18 - 2006

2. In this talk Analysis of S-Pol radar data How frequent and with what intensity do trade wind cumuli produce rain?  from a large scale perspective Analysis of sounding data Can we relate this rainfall to the vertical (dynamic) structure of the atmosphere? Can we provide statistics for modeling studies?

3. Radar analysis: S-Pol  S-Band horizontal (surveillance) scans  Time resolution: ~ 70 scans a day  a scan each 20 minutes  Filtering of ground / sea clutter, birds and Bragg scatter (10 dBZ threshold)  Z-R relation: Uijlenhoet, 2004  1 mm/h  24 dBZ > 10 dBZ 20 km 100 km RawFiltered

4. Data selection based on range attenuation 20 km - 60 km z ~ 500 m The radar observes rain below cloud base (~ 600 m)

5. Area rainfall during RICO: Time series and probability of rainfall

6. Time series of area rainfall many small rain peaks “trade cu period” Mean echo coverage: 1.7 % Mean rainrate 0.026 mm/h ~ 18 W/m2

7. Rainfall probability 50 % How much do the small peaks contribute to the total rainfall? 0.125 mm/h

8. Echo structure and rain rates Coverage = 2.55 % R echo = 2.12 mm/h Echo cells (3 km) Dec 22, 05 UTC Coverage = 1.41 % R echo = 1.52 mm/h Rainband (> 20 km) Dec 29, 01 UTC

9. Can we relate the relative amount of rainfall to the atmospheric profiles ?

10. Three type of soundings: 1)Spanish Point on Barbuda 2)R/V Seward Johnson 3)C-130 dropsondes Sounding analysis

11. NE radar domain  q SST

12. Sounding analysis Do soundings relate to small rain events? Relate each sounding to a 6 hour average area rainrate Group by following rainrates in mm/h : 1.0 – 0.002 ~ 1.4 Wm -2 2.0.002 – 0.02~ 15 Wm -2 3.> 0.02 NE Dec 13, 14, 15 Jan 9, 13, 14, 18

13. Vertical profiles Specific humidity 1.5 g/kg 0 - 0.002 0.002 - 0.02 >0.02

14. Vertical profiles Temperature

15. Vertical profiles Relative humidity 15-20 %

16. Rainfall versus cloud depth Estimating cloud depth for each sounding Using a very simple parcel ascent scheme for a diluting air parcel: Air parcel released from max  v in the lower subcloud layer Giving small release excesses  l and  q t With entrainment rate inversely proportional to height of parcel Cloud base = LCL, cloud top  LZB (  v, parcel =  v )

17. Rainfall versus cloud depth

18. Some last thoughts… How do the LES simulations and profiles compare to these findings? Difficult to obtain a close correlation between parameters derived from soundings and the area rainfall –water vapor deficiency? –theta gradient in cloud layer? –…?

19. Random / scattered

20. Clusters?

21. Deeper convection

22. Comparison to other estimates Area rain rate [mm/h] S-Pol rain rate coincides with relative rain rate from surface station. Suggests that rain reaches the surface.