Subtropical
Clouds
The subtropical cloud-capped
marine boundary layer has a strong climate impact through the decks’
high solar reflectivity whereas the emitted long-wave radiation remains
close to clear sky emission (Hartmann et al., 1992). While our
understanding of the processes involved in the maritime warm clouds
(either large-scale processes or microphysics) is not complete, the
necessity of understanding the response of their radiative properties
to both the large-scale circulation and aerosol is relevant for predicting future climate
scenarios.
Southeast Pacific Stratocumulus
The Southeast Pacific Sc cloud deck (the focus of this study) has features that distinguish it from the planet’s other major stratocumulus decks. In particular, an imposing coastal topography – the Andes Cordillera – protects the deck from routine aerosol-laden continental outflow. The deck itself is characterized by higher cloud tops (Fig. 1, Zuidema et al., 2009) and more pronounced drizzle offshore (Leon et al., 2008). The orography also dictates along-shore winds, whose modulation affects downstream advection and thereby the cloud properties (Muñoz and Garreaud 2005). In a recent paper (Zuidema et al. 2009), we derived an empirical satellite-based estimate of the boundary layer height (Fig. 1).
FIG. 1. Mean cloud-top height fields for October 2005, 2006, and 2007 combined for (a) Terra night, at 2230 LT, (b) Aqua night, at 0130 LT, (c) Terra day, at 1030 LT, and (d) Aqua day, at 1330 LT. Values are based on the samples possessing a cloud fraction .90% only, with typically at least one-third of all samples contributing when cloud fractions, indicated by the contour lines, exceed 70%. Land elevations exceeding 3 km at 10-min spatial resolution are also indicated. (Zuidema et al. 2009)
Cloud-Aerosol Interaction
As reported by Bennartz et al. (2007), large
satellite-derived cloud droplet number concentrations (CDNC) are
retrieved along the Peru and Chile coast (17˚S-32˚S) but with a
significant reduction 10 degrees further west (Fig. 2). The objective
here is trying to understand the importance of the regional
circulation in order to determine such trait.
Twomey (1977) proposed that an increase of cloud nuclei by pollution (and an increase of the cloud droplet number concentration) under constant liquid water content can lead to an increase in the solar radiation reflected by clouds (albedo effect). Further analysis is being carried out in order to understand the albedo effect over these region.
Southeast Pacific Stratocumulus
The Southeast Pacific Sc cloud deck (the focus of this study) has features that distinguish it from the planet’s other major stratocumulus decks. In particular, an imposing coastal topography – the Andes Cordillera – protects the deck from routine aerosol-laden continental outflow. The deck itself is characterized by higher cloud tops (Fig. 1, Zuidema et al., 2009) and more pronounced drizzle offshore (Leon et al., 2008). The orography also dictates along-shore winds, whose modulation affects downstream advection and thereby the cloud properties (Muñoz and Garreaud 2005). In a recent paper (Zuidema et al. 2009), we derived an empirical satellite-based estimate of the boundary layer height (Fig. 1).
FIG. 1. Mean cloud-top height fields for October 2005, 2006, and 2007 combined for (a) Terra night, at 2230 LT, (b) Aqua night, at 0130 LT, (c) Terra day, at 1030 LT, and (d) Aqua day, at 1330 LT. Values are based on the samples possessing a cloud fraction .90% only, with typically at least one-third of all samples contributing when cloud fractions, indicated by the contour lines, exceed 70%. Land elevations exceeding 3 km at 10-min spatial resolution are also indicated. (Zuidema et al. 2009)
Cloud-Aerosol Interaction
Twomey (1977) proposed that an increase of cloud nuclei by pollution (and an increase of the cloud droplet number concentration) under constant liquid water content can lead to an increase in the solar radiation reflected by clouds (albedo effect). Further analysis is being carried out in order to understand the albedo effect over these region.
FIG 2: Cloud droplet number
concentration (colors) and liquid water path (contours) over the southeast Pacific from MODIS
instrument.