1. Lagrangian Analysis of Tropical Cirrus and Upper-Tropospheric Humidity Z. JOHNNY LUO City College of New York, CUNY

2. Acknowledgments Dr. William Rossow Dr. Graeme Stephens Dr. Thomas Vonder Haar Dr. Richard Johnson Dr. Dieter Kley And many others…

3. Tropical Cirrus Tropical cirrus are very different from cirrus we see in midlatitude

4. It started from my Ph.D. research Bill’s original plan for my thesis - “Covariability of tropical cirrus and upper- tropospheric water vapor” What this meant was not immediately clear to me back then.

5. Motivation Climatology of tropical deep convection, cirrus and UTWV shows that they are highly correlated with each other (e.g. Soden and Fu 1995). But from these monthly mean maps, we can’t infer any cause-effect relationship or processes responsible for the good correlation. Eulerian  Lagrangian

6. Satellite retrieval algorithm development  The split-window (11 & 12  m) to retrieve cirrus cloud-top height and emissivity (optical depth)  SSM/T2 (183 GHz) to retrieve upper-tropospheric humidity (tuned up to 6.7-  m radiances in clear sky)  3-hourly deep convection data (ISCCP IR)

7. Starting from where convection dies out, continue to follow the large-scale UT air trajectory (as determined from NCEP/NCAR analysis) for 5 days. The rationale is to sample the transition from deep convection to cirrus anvil to thin cirrus, as well as the associated variation of UTH along the trajectory. Luo and Rossow (2004) Lagrangian Trajectories

8. ISCCP Cloud Classification

9. Day 0Day 1 Day 2Day 3 Day 4Day 5

10. The decay of deep convection is immediately followed by the growth of cirrostratus and cirrus, and then the decay of cirrostratus is followed by the continued growth of cirrus. CirrusCirrostratus Cloud Amount Cloud top (mb) Tau Time from convection (days)

11. Separating detrained cirrus from in situ cirrus For each individual trajectory (which starts where convection dies), we track the detrained cirrus until they go to zero. All other cirrus that have no direct connection to convection are called in situ cirrus.

12. Averaged over the whole tropics, about half of the cirrus are formed in situ well away from convection. So, Lindzen’s iris hypothesis, even if 100% true, only applies to half of the tropical cirrus

13. Histogram of tropical cirrus lifetime Lifetime (hr) 48 Detrained Cirrus In Situ Cirrus

14. Cirrus Cases Clear Cases Upper tropospheric humidity (%) Time from convection (days) Relationship between cirrus and UTWV

15. Cirrus Cases Clear Cases Upper tropospheric humidity (%) Time from convection (days) This difference is 1-2 orders of magnitude greater than what cirrus can provide. The most likely mechanism for the moistening is dynamic transport.

16. PDFs of UT vertical velocity for cirrus (solid) and clear (dashed) cases Clear Cirrus

17. All histograms are for clear-sky UTH, but 3 types of clear sky: 1) one that has upstream cirrus (solid), 2) one that has downstream cirrus (dashed) 3) one that stays clear for the past and future (dotted).

18. CSU GISS Continue with UTH topics but use in situ measurements this time

19. MOZAIC ( Measurements of Ozone and Water Vapour by Airbus In-Service Aircraft ) sponsored by the European Union 1994 ~ present Luo et al. (2007) Flying between 300-200 hPa

20. Bimodal distribution of UTH: What does this tell us about tropical upper troposphere? UTH (upper- tropospheric humidity) histogram

21. For each aircraft measurement, we track backward in time to see how long the air parcel has traveled since its last exposure to deep convection.

22. Close to convection Far from convection Now things start to make sense: the moist mode is due to convetive moistening whereas the dry mode is due to subsidence drying. UTH histograms 010050100050

23. Close to convection Far from convection Now things start to make sense: the moist mode is due to convetive moistening whereas the dry mode is due to subsidence drying. UTH histograms 010050100050

24. Close to convection Far from convection UTH histograms

25. Close to convection Far from convection Now things start to make sense: the moist mode is due to convetive moistening whereas the dry mode is due to subsidence drying. UTH histograms Nawrath 2002

26. Conceptual model of water vapor evolution (Nawrath 2002) UTH decreases slower when there is cirrus

27. Flight level (hPa) RHi Vertical structure of UTH Luo et al. (2007)

29. Luo et al. 2008

30. Ice super-saturation

31. “Mysterious” moistening Most prevalent flight level: 238 & 263 hPa Temperature Specific humidity (normalized) Relative humidity

32. Summary Lagrangian analysis of satellite data adds new insights into our understanding of tropical cirrus and UTH: 1. Decay of deep convection is followed by growth of thick & thin cirrus and then the decay of thick cirrus is followed by the continued growth of thin cirrus 2. About half of the tropical cirrus are formed in situ having no direct connection with convection 3. Cirrus does not moisten the UT. Rather, it is dynamic transport that does the job and makes cirrus. Analysis of long-term aircraft in situ measurements of UTH: 1. Consistent with satellite analysis concerning the relationship b/w cirrus and UTH 2. Comparison with ECMWF analysis reveals possible model deficiency in representation of cloud and convection.

33. Summary Lagrangian analysis of satellite data adds new insights into our understanding of tropical cirrus and UTH: 1. Decay of deep convection is followed by growth of thick & thincirrus and then the decay of thick cirrus is followed by the continued growth of thin cirrus 2. About half of the tropical cirrus are formed in situ having no direct connection with convection 3. Cirrus does not moisten the UT. Rather, it is dynamic transport that does the job and makes cirrus. Analysis of long-term aircraft in situ measurements of UTH: 1. Consistent with satellite analysis concerning the relationship b/w cirrus and UTH 2. Comparison with ECMWF analysis reveals possible model deficiencies in the representations of cloud and convection.

34. Thank you! Contact: Johnny Luo Dept. Earth & Atmospheric Sciences City College of New York, CUNY luo@sci.ccny.cuny.edu