Journal article

Microphysical variability in southeast Pacific Stratocumulus clouds: Synoptic conditions and radiative response

Painemal D, Zuidema P ...see all

Atmospheric Chemistry and Physics, vol. 10, issue 13 (2010) pp. 6255-6269

  • 19


    Mendeley users who have this article in their library.
  • 25


    Citations of this article.
Sign in to save reference


Synoptic and satellite-derived cloud property vari-ations for the southeast Pacific stratocumulus region associ-ated with changes in coastal satellite-derived cloud droplet number concentrations (N d) are explored. MAX and MIN N d composites are defined by the top and bottom terciles of daily area-mean N d values over the Arica Bight, the re-gion with the largest mean oceanic N d , for the five Octo-ber months of 2001, 2005, 2006, 2007 and 2008. The abil-ity of the satellite retrievals to capture composite differences is assessed with ship-based data. N d and ship-based accu-mulation mode aerosol concentrations (N a) correlate well (r =0.65), with a best-fit aerosol activation value d lnN d d lnN a of 0.56 for pixels with N d >50 cm −3 . The adiabatically-derived MODIS cloud depths also correlate well with the ship-based cloud depths (r =0.7), though are consistently higher (mean bias of almost 60 m). The MAX-N d composite is character-ized by a weaker subtropical anticyclone and weaker winds both at the surface and the lower free troposphere than the MIN-N d composite. The MAX-N d composite clouds over the Arica Bight are thinner than the MIN-N d composite clouds, have lower cloud tops, lower near-coastal cloud albe-dos, and occur below warmer and drier free tropospheres (as deduced from radiosondes and NCEP Reanalysis). CloudSat radar reflectivities indicate little near-coastal precipitation. The co-occurrence of more boundary-layer aerosol/higher N d within a more stable atmosphere suggests a boundary layer source for the aerosol, rather than the free troposphere. The MAX-N d composite cloud thinning extends offshore to 80 • W, with lower cloud top heights out to 95 • W. At 85 • W, the top-of-atmosphere shortwave fluxes are signif-icantly higher (∼50%) for the MAX-N d composite, with thicker, lower clouds and higher cloud fractions than for the MIN-N d composite. The change in N d at this loca-Correspondence to: D. Painemal ( tion is small (though positive), suggesting that the MAX-MIN N d composite differences in radiative properties pri-marily reflects synoptic changes. Circulation anomalies and a one-point spatial correlation map reveal a weakening of the 850 hPa southerly winds decreases the free tropospheric cold temperature advection. The resulting increase in the static stability along 85 • W is highly correlated to the in-creased cloud fraction, despite accompanying weaker free tropospheric subsidence.

Get free article suggestions today

Mendeley saves you time finding and organizing research

Sign up here
Already have an account ?Sign in

Find this document

Get full text


  • D. Painemal

  • P. Zuidema

Cite this document

Choose a citation style from the tabs below

Save time finding and organizing research with Mendeley

Sign up for free