A new look at – Tropical Mid-Troposphere Clouds P. Zuidema, B. Mapes, J. Lin, C. Fairall P. Zuidema, B. Mapes, J. Lin, C. Fairall CIRES/CDC NOAA/ETL Boulder, CO RSMAS/MPO Miami, FL Why….”a new look” ??? 2 recent tropical convective oceanic field campaigns included co-located cloud and Doppler precipitation radar  New observations and data analysis provide a fresh look into deep convective processes and its associated cloudiness

TOGA COARE: TOGA COARE: 3rd cloud population w/ cloud top heights between 5-9 km. 3rd cloud population w/ cloud top heights between 5-9 km. Johnson et al, 1999: Trimodal characteristics of convection Cloud vertical structure inferred indirectly (precip radar & sondes) Linked to: - melting-level stable layers - dry air intrusions from extratropics

 m/s bins

Eastern Pacific Investigation of Climate (EPIC) Sept. 2001, 10N&95W (Raymond et al., 2004, BAMS) equator 40N Low-level wind Upper wind Joint Air-Sea Monsoon Interaction Experiment (JASMINE) May 1999 (monsoon onset), Bay of Bengal (Webster et al., 2002, BAMS)

Cloud radar: attenuates with water vapor, liquid and precip point measurement but continuous ~ 20 dBZ max EPIC (21 day)JASMINE-convective (10 days) Height (km) Melting-level outflow

Hurricane JulietteRHB leaves 10N, arrives 5N Time series of coincident sonde RH at 95W, 10N

EPIC meridional wind Most mid-tropospheric dry layers related to the southerly phase of the easterly waves meridional zonal RH < 30%, 4-8km Strong southerly Or Weak northerly component Episodic southerly mid-tropospheric advection of dry air apparent in mean NCEP Sept. mean RH & V along 110 W

Sept. 21: pronounced 6-7 km dry air layer, south-south- westerly winds with easterly winds above 8-14 km anvil cloud resides above dry layer (suggests sublimation) Surface-based convection mitigated by both 3-5 km and 6-7 km dryness Surface Rainfall rates Sublimation supported by precipitation radar divergence profile ! large-scale (~50 km range) divergence calculated from precipitation radar shown in blue (solid line=divergence, dotted line=convergence)

Two independent estimates of latent cooling “Q” from sublimation ! 1.Cloud radar IWC flux:  (IWC)/  z * fall speed*latent heat = Q 2. Horizontal wind divergence = ∂(vertical velocity)/∂p ~ ∂Q/∂p*1/static stability - Large-scale process (divergences over a 100 km^2 area) apparently has a microphysical origin (melting of ice). convincingly documented thanks to combined analysis of the two radars -horizontal divergence will act to simultaneously spread and thin The (top of the) dry layer, which is now cooler and moister Frequency of Layers with Lapse rates > -5, -4, -3 K/km

convective Height (km) nonconvective Relative humidity time series On to…. JASMINE…

Meteosat-5 Infrared Imagery Mean diurnal cycle of 210K Zuidema, 2003 ~15 m/s Dave Lawrence

JASMINE squall (wave?) prevailing wind Zuidema, 2003

SUMMARY & CONCLUSIONS: Remarkable consistency between surface rainfall rates, vertically-pointing cloud radar, and large-scale calculated precipitation radar divergences; (full time series posted through New mechanism noted by which dry air intrusions influence tropical cloud vertical structure: anvils snowing into dry layers, moistening and cooling Background JASMINE cloud images courtesy of U. of Washington JASMINE webpage Implications and ?? for TWP-ICE: EPIC and JASMINE took place “far” from land - TWP-ICE likely to capture even more complexity. What role do dry air intrusions play, if any ? If in evidence, how can models reproduce their influence on convection and mean climatology ? Might divergence structures other than convective/stratiform also be seen ? What cloud overlap constructions best describe the various regions ? Dry air intrusions can be an integral dynamical component (not just a random external forcing)