EPIC 2001 SE Pacific Stratocumulus Cruise 9-24 October 2001 Rob Wood, Chris Bretherton and Sandra Yuter (University of Washington) Chris Fairall, Taneil Uttal (NOAA/ETL) Bob Weller (Woods Hole OI)

Clouds types, SST and wind stress in the East Pacific

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

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 cruise 9-24 Oct. 2001

Radiosonde observations  qvqv Cloud baseSharp PBL inversion At Buoy Figure by Kim Comstock

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

[m s -1 ] ECMWF VERTICAL VELOCITY [dBZ] Diurnal Cycle

Large scale observations of the diurnal cycle of low cloud (cont.) TRMM TMI (microwave imager) observations of LWP Wood, Bretherton, and Hartmann (2002) SE PACIFIC [85W, 20S], LOCAL TIME [hr] LWP [g m -2 ]

Geographical variations MEAN LWP AMPLITUDE [fraction] TIME OF MAXIMUM LWP Strongest diurnal cycle of LWP found in the regions of low cloud to the west of continents Larger amplitudes in southern hemisphere Peak LWP at hr showing diurnal cycle of insolation is key modulator Summer max. in amplitude

Diurnal cycle of subsidence w s, entrainment w e, and  z i /  t NIGHT DAY NIGHT DAY wsws wewe dz i /dt  w e = 0.24 cm s -1 ;  w s = 0.26 cm s -1 ;   z i /  t = 0.44 cm s -1  z i /  t + u  z i = w e - w s  0.05 cm s -1

Mixed layer budgets Latent Evap zizi Free trop. Mixed layer Sensible Heating qTqT SLSL Precip EntrainmentLWSW Net radiative flux divergence qTqT SLSL Ocean

Estimating budget terms LE zizi SHRain Entrainment LWSW Ocean bulk flux algorithm using Ron Brown met measurements 3hr radiosonde profiles, observed LWP and Fu-Liou radiation scheme cloud radar, ECMWF subsidence, + MODIS BL depth climatology cloud radar + microphysical model Advection terms estimated using NCEP and ECMWF reanalyses Storage terms estimated using sonde profiles

Solar absorption and drizzle evaporative stabilization zizi Ocean Solar absorption SW Drizzle evaporaton warmingcooling Evaporative cooling

Drizzle + solar decoupling? Strong TKE source in cloud Evaporating drizzle suppresses TKE below cloud Drizzle Solar Local time Buoyancy flux height [m]

Diurnal cycle of convective velocity scale Drizzle and solar radiation reduce mean w * by comparable amounts

Sample of C-band scanning radar and coincident MMCR dBZ km

Meth Blue Rain Rate Number/second Z=58R 1.1

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) cm g m mm Liquid water pathDroplet 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 ( m). Observed LWC mainly at 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 cloud drop conc. Boundary layer deeper than current global models; well-mixed in early evening but near total shut-down of entrainment in early morning due to combination of solar absorption and drizzle evaporation