A new look atA new look at – – Tropical Mid-Troposphere Tropical Mid-Troposphere

CloudsClouds P. Zuidema, B. Mapes, J. Lin, C. P. Zuidema, B. Mapes, J. Lin, C.

FairallFairall CIRES/CDC NOAA/ETL Boulder, CO

RSMAS/MPO Miami, FL

Why….”a new look” ???

2 recent tropical convective oceanic field campaigns includedco-located cloud and Doppler precipitation radar

New observations and data analysis provide a fresh lookinto deep convective processes and its associated cloudiness

TOGA COARE: TOGA COARE: 3rd cloud population 3rd cloud population

w/ cloud top w/ cloud top heights between 5-heights between 5-9 km.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)

Heig

ht (k

m)

14

6

10

2

0

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

zona

l

RH < 30%, 4-8km

Strong southerlyOrWeak northerlycomponent

Episodic southerly mid-tropospheric advection of dry air apparent in mean

NCEP 1990-2000 Sept. meanRH & 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

SurfaceRainfallrates

• Sublimation supported byprecipitation radar divergenceprofile !

large-scale (~50 km range) divergence calculated from precipitation radarshown 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) apparentlyhas a microphysical origin (melting of ice). convincingly documented thanks to combined analysis of the two radars

-horizontal divergence will act to simultaneously spread and thinThe (top of the) dry layer, which is now cooler and moister

Frequency of Layers withLapse rates> -5, -4, -3 K/km

convective

Heig

ht (k

m)

14

6

10

2

0

nonconvective

Relative humidity time seriesOn to….JASMINE…

Meteosat-5 Infrared Imagery

Mean diurnal cycle of 210K

Zuidema, 2003

~15 m/s

Dave Lawrence

JASMINE JASMINE squallsquall(wave?)(wave?)

prevailing wind

Zuidema, 2003

SUMMARY & CONCLUSIONS:Remarkable consistency between surface rainfall rates, vertically-pointingcloud radar, and large-scale calculated precipitation radar divergences;(full time series posted through http://www.rsmas.miami.edu/users/pzuidema)

New mechanism noted by which dry air intrusions influence tropical cloudvertical 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 captureeven more complexity.

What role do dry air intrusions play, if any ? If in evidence, how can modelsreproduce 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)