A characterization of clouds over the Great Barrier Reef and the role of local forcing

Abstract

A characterization of cloud properties associated with precipitation in the region around the Great Barrier Reef (GBR) is constructed using decadelong (2007-2017) satellite observations from Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) combined with CloudSat. The spatial and vertical distributions of low-level cloud properties over the region are also investigated and discussed. In general, different cloud types are observed over different regions and vary by season: high clouds are dominant over the low latitudes in summer, altocumulus are mainly observed over northeast Queensland and low-level clouds are dominant over the ocean and coast during the winter months at higher latitudes under a trade wind regime. A strong latitudinal dependence of total precipitation across the Greater GBR region is identified with a significant orographic enhancement near Cairns in the wet tropics. MODIS and CloudSat-CALIPSO cloud observations show good agreement on significant differences in low-level cloud microphysical properties between the land and the ocean. The largest land-ocean differences in warm cloud microphysical properties are found over the mid-latitudes near 18 S, which is strongly associated with orographic forcing, with these enhancements extending further east to the coral reef area. However, the frequency of warm cloud is not enhanced upwind of the mountains in the wet tropics. In addition, no significant differences in warm cloud properties between the actual GBR and the open ocean are identified. These results suggest that low-level clouds over the GBR do not show any significant response to the reef-related microphysical perturbations.

Interactions between trade-wind clouds and local forcings over the Great Barrier Reef: A case study using convection-permitting simulations

“…It is interesting to note that the orographic enhancement of the low-level cloud fraction, extending to the eastern water area, potentially provides a sheltered area for the coral reefs, protecting them from severe bleaching through reducing the solar radiation heating. This result is consistent with the observational analysis presented by Zhao et al (2022), which highlighted a notable increase in the frequency of low-level clouds associated with orographic enhancement in the Wet Tropics. Figure 9 shows the map of accumulated precipitation over the inner-most domain from 1 km WRF simulations from the CTRL-run, and the difference between CTRL-run and sensitivity studies, respectively.…”

“…Bonell and Gilmour, 1980), with the Bellenden Ker Top station receiving over 8000 mm of annual precipitation (Herwitz, 1986) on average. Zhao et al (2022) found significant orographic enhancement of low-level clouds not only over the Wet Tropics, but also over the upwind ocean extending partially over the GBR. It is therefore of interest to examine any upwind effect of orographic enhancement on shallow cloud and precipitation through high-resolution numerical simulations, where interactions of local variability associated with topography and coastal processes are better resolved.…”

“…Trade wind cumuli are ubiquitous across the subtropical oceans (Warren et al, 1988;Norris, 1998;Eastman et al, 2011;Boucher et al, 2013;Rauber et al, 2007), including the Great Barrier Reef (GBR) (Zhao et al, 2022).…”

“…Over the GBR, a recent climatology study by Zhao et al (2022) revealed little to no difference in low-level cloud…”