Cirrus clouds and deep convection in the tropics: Insights from CALIPSO and CloudSat

Abstract

[1] Using a 2-year data set of combined lidar and cloud radar measurements from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and CloudSat satellites, the occurrence of tropical cirrus and deep convective clouds is studied. The cloud identification algorithm takes advantage of the ability of the radar to probe deep precipitating clouds and of the lidar to sample even subvisual cirrus clouds. Examined are the frequency of occurrence and the geographical distribution of these clouds, and their apparent interconnections. There is a strong apparent diurnal variability in tropical cirrus mainly over land, with significantly more cirrus detected at night compared to day, but no clear diurnal pattern in deep convective activity. CALIPSO daylight signal noise effects do not appear to be not responsible for the diurnal cirrus pattern, because high, thin tropopause transitional layer (TTL) cirrus do not show a clear diurnal effect. Stratifying the global results by estimated visible cloud optical depth t, we find that most of the planet's subvisual (t < $0.03) cirrus clouds occur in the tropics and are more frequent at night and over ocean; thin ($0.03 < t < $0.3) cirrus have their highest global frequencies over equatorial landmasses and in the west Pacific region, and are also more frequent at night but occur mainly over land; and opaque ($0.3 < t < $3.0) cirrus are spread globally and tend to occur during the day over ocean. Although it is unknown which of the several proposed cirrus cloud formation mechanisms are key in the tropics, the close association of cirrus with convective clouds implies that tropical cirrus are linked to deep convective activity, with the likely exception of TTL cirrus clouds.

Tropical tropospheric ozone columns from nadir retrievals of GOME-1/ERS-2, SCIAMACHY/Envisat, and GOME-2/MetOp-A (1996–2012)

“…The second basic assumption of the CCD method refers to the fact that the tropopause (∼ 18 km or ∼ 100 hPa) lies close to the top of the DCC. These clouds are high, thick, and bright with greatest occurrence rates over the Intertropical Convergence Zone (ITCZ), the western Pacific Ocean, and the Indian Ocean (Sassen et al, 2009;Hong et al, 2007). Due to the immigration of the ITCZ, these clouds are located south, over the western and central Pacific Ocean, northern South America, and equatorial Africa in boreal winter and spring, whereas in boreal summer the highest DCC occurrences are located over the Indonesian region and the Bay of Bengal (Sassen et al, 2009).…”

“…These clouds are high, thick, and bright with greatest occurrence rates over the Intertropical Convergence Zone (ITCZ), the western Pacific Ocean, and the Indian Ocean (Sassen et al, 2009;Hong et al, 2007). Due to the immigration of the ITCZ, these clouds are located south, over the western and central Pacific Ocean, northern South America, and equatorial Africa in boreal winter and spring, whereas in boreal summer the highest DCC occurrences are located over the Indonesian region and the Bay of Bengal (Sassen et al, 2009). Figure 3a shows the distribution of the DCCs in January and August 2008 for SCIAMACHY ((CF > 0.8 and CTH > 9 km) SACURA) and GOME-2 ((CF > 0.8 and CTH > 7 km) FRESCO), indicating the ITCZ.…”

Cirrus cloud retrieval with MSG/SEVIRI using artificial neural networks

“…All connections between the neurons within the MLP are in the forward direction (input layer → hidden layer(s) → output layer). Connections backward or within a layer are forbidden (Rumelhart et al, 1986). The value of a neuron is calculated by processing the output from the preceding neurons connected to that neuron and the corresponding weights through an activation function.…”

Improvement of Cirrus Cloud-Top Height Estimation Using Geostationary Satellite Split-Window Measurements Trained with CALIPSO Data

“…Many clouds that have a wide range of visible optical depth (τ) properties, i.e., from subvisible (τ < 0.03) through thin (0.03 < τ < 0.3) to opaque (0.3 < τ), have their tops at this altitude. (Note, this classification is traditional, e.g., Sassen et al (2009).) Figure 2b shows the results of the CPR.…”

“…In contrast, a lidar observes another type of optically thin cirriform clouds. These clouds, which extend around the tropopause, have various origins and they are not necessarily direct extensions of cumulus clusters (Sassen et al 2009). Radiation observation in the atmospheric window range from geostationary satellites might not have sufficient sensitivity to detect such very thin clouds.…”