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A continental gravity wave influence on remote marine SE Pacific cloud. Robert Wood 1 , Christopher Bretherton 1 , Peter Caldwell 1 , Martin Köhler 2 , Rene Garreaud 3 , and Ricardo Muñoz 3 University of Washington, Seattle, USA ECMWF, Reading, UK
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Robert Wood1, Christopher Bretherton1,
Peter Caldwell1, Martin Köhler2, Rene Garreaud3, and Ricardo Muñoz3
University of Washington, Seattle, USA
ECMWF, Reading, UK
Department of Geophysics, Universidad de Chile, Chile
East Pacific Investigation of Climate (Bretherton et al. 2003)
Shipborne observations with NOAA Ronald H Brown
Instruments include….MMCR, C-band radar, microwave radiometer, ceilometer, radiometers, met tower
Special MM5 runs performed by Rene Garreaud and Ricardo Muñoz (Universidad de Chile, Chile)
Special ECMWF run performed using new vertical wind diagnostic by Martin Köhler (ECMWF, UK)
Important climatological effects…strong SW cloud forcing but weak LW forcing….…net cooling effect
ECMWF VERTICAL VELOCITY
Diurnal cycle – The view from EPIC 2001(85 W, 20S)
Surprising diurnal cycle in subsidence…. …results in strong diurnal cycle of cloud top height… …that enhances diurnal cycle of LWP
LOCAL HR 18 0 6 12 18
zi/t + u•zi= we - ws
NIGHT DAY NIGHT DAY
EPIC 2001 [85W, 20S]Diurnal cycle of subsidencews, entrainmentwe, andzi/t
sws=0.26 cm s-1
szi/t=0.44 cm s-1
Conclusion: Subsidence and entrainment contribute equally to diurnal cycle of MBL depth
Mean divergence Diurnal difference (6L-18L)
17S-73W 22S-71W 21S-76W
Diurnal amplitude equal to or exceeds synoptic variability (here demonstrated using 800 hPa potential temperature variability) over much of the SE Pacific, making the diurnal cycle of subsidence a particularly important mode of variabilityDiurnal vs. synoptic variability (MM5)
(a) diurnally varying forcings including subsidence rate
(b) diurnally varying forcings but constant (mean) subsidence
We thank Chris Fairall, Taneil Uttal, and other NOAA staff for the collection of the EPIC 2001 observational data on the RV Ronald H Brown. The work was funded by NSF grant ATM-0082384 and NASA grant NAG5S-10624.
Bretherton, C. S., Uttal, T., Fairall, C. W., Yuter, S. E., Weller, R. A., Baumgardner, D., Comstock, K., Wood, R., 2003: The EPIC 2001 Stratocumulus Study, Bull. Am. Meteorol. Soc., submitted 1/03.
Garreaud, R. D., and Muñoz, R., 2003: The dirnal cycle in circulation and cloudiness over the subtropical Southeast Pacific, submitted to J. Clim., 7/03.
Wood, R., Bretherton, C. S., and Hartmann, D. L., 2002: Diurnal cycle of liquid water path over the subtropical and tropical oceans. Geophys. Res. Lett.10.1029/2002GL015371, 2002