EPIC 2001 SE Pacific Stratocumulus Cruise

9-24 October 2001Chris Bretherton and Sandra Yuter (U. Wash.)

Chris Fairall, Taneil Uttal (NOAA/ETL)

Bob Weller (WHOI)

Goals

• Document cloud and boundary layer structure in the SE Pacific

• Assess the importance of drizzle processes to cloud thickness and extent

• Compare results with other Sc regimes and with large-scale models

• Maintain WHOI IMET buoy at 20S 85W

NOAA/ETL (surface met., fluxes, mm radar, lidar)

Participants

Participants

UNAM (aerosol concentration and characterization)

Participants

WHOI (CTDs, IMET buoy)

Participants

University of Washington (sondes, 5 cm scanning radar,

meth blue, cloud photos)

EPIC Sc cruise9-24 Oct. 2001

3 hr rawinsonde launches

(Kim Comstock, UW)

cld top

cld base

LCL

Cloud top and dBZ (MMCR), base (ceilometer), LCL (surf. met.)

[m s-1] ECMWF VERTICAL VELOCITY

[dBZ]10

-10

0

DiurnalCycle

Sample of C-band scanning

radar and coincident

MMCR

dBZ

0530 0730

Meth BlueRain Rate

Num

ber/

seco

ndZ=58R1.1

Remotely-sensed cloud microphysics

(Rob Wood, UW)

…UNAM also found a strong diurnal signal in submicron aerosol conc.

MODIS 10/16/2001; 10:00 Local (16:00 UTC)

1 3 10 30 100 300 1000 cm-3

0 50 100 150 200 250 300 g m -2

0 5 10 15 20 25 30 mm

Liquid water path Droplet concentrationEffective radius

SHIP

250 km

Comparison of 6-day mean 20S 85W profiles with models

• All models (esp CAM) have too shallow a PBL.• CAM2 LWC all in lowest 3 levels (70-630 m).• Observed LWC mainly at 800-1300 m.

(Peter Caldwell, UW)

Conclusions• A remarkable dataset was gathered

documenting both spatial and diurnal variability of the SE Pacific Sc regime

• Pronounced diurnal cycle, amplified by subsidence wave from S America.

• Mesoscale drizzle cells ubiquitous, especially at night; rain mostly evaporates above surface, sensitive to cld drop conc.

• Boundary layer deeper than current global models; well-mixed in early evening.