Tropical cirrus cloud properties derived from TOGA/COARE airborne polarization lidar

Sassen, Kenneth; Benson, Randall P.; Spinhirne, James D.

doi:10.1029/1999gl010946

Cited by 30 publications

(27 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Direct measurements of lidar‐ratio profiles at 532 nm by Eloranta et al [2001] yielded a distribution of S par occurrences with greater similarity to our measurements (most of the data between 10 and 30 sr), but the center of the distribution appears to be at slightly larger S par values than at 355 nm, and S par data >30 sr are observed (central North America site). On the other hand, particle depolarization ratios of Sassen et al [2000] (δ par between 35% and 60% for T C < −25°C; tropical western Pacific Ocean; measurement wavelength of 1064 nm), Sassen and Benson [2001] (>30% for T C < −30°C for both zenith and off‐zenith (>4°) data subsets), and of Eloranta et al [2001] (most δ par > 30%) agree well with our observations, while the depolarization data of Del Guasta et al [1993] are significantly smaller with values predominantly <22%. The discrepancies between the cirrus optical data sets mentioned are probably due to the different geographical locations at which the cirrus clouds were observed, rather than to differing experimental geometries, or data reduction methods.…”

Section: Observationssupporting

confidence: 87%

Correlations among the optical properties of cirrus‐cloud particles: Microphysical interpretation

Reichardt

Heß

et al. 2002

J. Geophys. Res.

View full text Add to dashboard Cite

[1] Cirrus measurements obtained with a ground-based polarization Raman lidar at 67.9°N in January 1997 reveal a strong positive correlation between the particle optical properties, specifically depolarization ratio d par and extinction-to-backscatter (lidar) ratio S par , for d par < $40%, and an anticorrelation for d par > $40%. Over the duration of the measurements, both particle properties vary systematically. This effect is particularly pronounced in the case of d par , which decreases significantly with time. The analysis of lidar humidity and radiosonde temperature data shows that the measured optical properties stem from scattering by dry solid ice particles, while scattering by supercooled droplets, or by wetted or subliming ice particles, can be excluded. For the microphysical interpretation of the lidar measurements, ray-tracing computations of particle scattering properties have been used. The comparison with the theoretical data suggests that the observed cirrus data can be interpreted in terms of size, shape, and growth of the cirrus particles, the latter under the assumption that the lidar measurements of consecutive cloud segments can be mapped on the temporal development of a single cloud parcel moving along its trajectory: Near the cloud top in the early stage of cirrus development, light scattering by nearly isometric particles that have the optical characteristics of hexagonal columns (short, column-like particles) is dominant. Over time, the ice particles grow, and as the cloud base height extends to lower altitudes characterized by warmer temperatures they become morphologically diverse. For large S par and depolarization values of $40%, the scattering contributions of column-and plate-like particles are roughly the same. In the lower ranges of the cirrus clouds, light scattering is predominantly by plate-like ice particles. This interpretation assumes random orientation of the cirrus particles. Simulations with a simple model suggest, however, that the positive correlation between S par and d par , which is observed for depolarization ratios <40% mainly at low cloud altitudes, can be alternatively explained by horizontal alignment of a fraction of the cirrus particle population.

show abstract

Section: Observationssupporting

confidence: 87%

Correlations among the optical properties of cirrus‐cloud particles: Microphysical interpretation

Reichardt

Heß

et al. 2002

J. Geophys. Res.

View full text Add to dashboard Cite

show abstract

“…The cloud base was typically found about 2 km below cloud top at both tropical sites. A higher mean tropopause height of 16.9 km over the western Pacific warm pool [ Sassen et al , 2000] in contrast to the 16.3 km height over the Maldives (see Table 2) implies differences in the meteorological conditions between both regions. High sea surface temperatures in the western Pacific region are also supposed to enhance deep convection [ Ramanathan and Collins , 1991; Liu and Zipser , 2005].…”

Section: Resultsmentioning

confidence: 99%

“…However, especially in the tropics vertically and temporally resolved measurements of cirrus cloud properties are still scarce. Recent studies have focused on the western Pacific warm pool [ Platt et al , 1998, 2002; Heymsfield et al , 1998; Sassen et al , 2000; Comstock et al , 2002]. Other lidar statistics of cirrus cloud properties in the tropics are available only for the Seychelles [ Pace et al , 2003] and eastern India [ Sunilkumar and Parameswaran , 2005].…”

Section: Introductionmentioning

confidence: 99%

Cirrus optical properties observed with lidar, radiosonde, and satellite over the tropical Indian Ocean during the aerosol‐polluted northeast and clean maritime southwest monsoon

et al. 2007

View full text Add to dashboard Cite

[1] Cirrus formation and geometrical and optical properties of tropical cirrus as a function of height and temperature are studied on the basis of INDOEX (Indian Ocean Experiment) lidar and radiosonde measurements and satellite observations of deep convection causing the generation of anvil cirrus. Lidar and radiosonde measurements were conducted at Hulule (4.1°N, 73.3°E), Maldives, during four field campaigns carried out in FebruaryMarch 1999 and March 2000 (northeast (NE) monsoon season, characterized by increased concentrations of anthropogenic aerosols over the Indian Ocean) and in July and October 1999 (southwest (SW) monsoon season, characterized by clean maritime conditions). As a result of a stronger impact of deep convection on cirrus formation during the SW monsoon season, cirrus clouds covered the sky over the lidar site in only 35% (NE), but 64% (SW) of the measurement time. Subvisible cirrus (optical depth 0.03), thin (optical depth from 0.03 to 0.3), and opaque cirrus (optical depth !0.3) were observed in 18%, 48%, and 34% (NE) and in 8%, 52%, and 40% (SW) out of all cirrus cases, respectively. Mean midcloud heights were rather similar with values of 12.9 ± 1.5 km (NE) and 12.7 ± 1.3 km (SW). In 25% of the cases the cirrus top height was found close to the tropopause. Mean values of the multiple-scattering-corrected cirrus optical depth, cirrus layer mean extinction coefficient, and extinction-to-backscatter ratio were 0.25 ± 0.26 (NE) and 0.34 ± 0.29 (SW), 0.12 ± 0.09 km À1 (NE) and 0.12 ± 0.10 km À1 (SW), and 33 ± 9 sr (NE) and 29 ± 11 sr (SW), respectively. A functional dependency of the extinction coefficient of the tropical cirrus on temperature is presented. All findings are compared with several other cirrus lidar observations in the tropics, subtropics, and at midlatitudes. By contrasting the cirrus optical properties of the different seasons, a potential impact of anthropogenic particles on anvil cirrus optical properties was examined. Differences in the cirrus extinction-to-backscatter ratio suggest that NE monsoon anvil cirrus originating from deep-convection cumulus clouds had more irregularly shaped and thus slightly larger ice crystals than respective SW monsoon anvil cirrus. Because the meteorological conditions were found to vary significantly between the seasons, an unambiguous identification of the influence of Asian haze on cirrus optical properties is not possible.

show abstract

“…Even the question of how high tropical DCC tops penetrate to, and so create anvil cirrus clouds at the detrainment level, is a matter of debate. While airborne lidar data from the TOGA/CORE project showed frequent cirrus near the tropopause in association with deep convection [ Sassen et al , 2000], most research indicates a lower detrainment level, which suggests that TTL cirrus are not directly derived from anvils. Field projects in various parts of the tropics are typically brief, so it should not be surprising that varied conclusions have been drawn about deep convection and cirrus clouds.…”

Section: Discussionmentioning

confidence: 99%

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

2009

Self Cite

View full text Add to dashboard Cite

[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.

show abstract

Tropical cirrus cloud properties derived from TOGA/COARE airborne polarization lidar

Cited by 30 publications

References 15 publications

Correlations among the optical properties of cirrus‐cloud particles: Microphysical interpretation

Correlations among the optical properties of cirrus‐cloud particles: Microphysical interpretation

Cirrus optical properties observed with lidar, radiosonde, and satellite over the tropical Indian Ocean during the aerosol‐polluted northeast and clean maritime southwest monsoon

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

Contact Info

Product

Resources

About