A sub‐tropical cirrus clouds climatology from Reunion Island (21°S, 55°E) lidar data set

Cadet, Bertrand; Goldfarb, L.J.B.; Faduilhe, Denis; Baldy, S.; Giraud, Vincent; Keckhut, Philippe; Réchou, Anne

doi:10.1029/2002gl016342

Cited by 39 publications

(28 citation statements)

References 18 publications

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“…5520 E. Giannakaki et al: Characteristics of cirrus clouds over a lidar station Comstock and Ackerman (2002) have studied the optical and geometrical properties of tropical cirrus clouds and found that high clouds occur on average 44% of the time. Sub-tropical cirrus clouds are present more frequently at austral summer than the austral winter as Cadet et al (2003) have shown. The same study showed that 65% of the total cirrus observations are characterized as sub-visual, with an optical thickness of less than 0.03.…”

Section: Introductionmentioning

confidence: 66%

Optical and geometrical characteristics of cirrus clouds over a Southern European lidar station

Giannakaki¹,

Balis²,

Amiridis

et al. 2007

Atmos. Chem. Phys.

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Abstract. Optical and geometrical characteristics of cirrus clouds over Thessaloniki, Greece (40.6 • N, 22.9 • E) have been determined from the analysis of lidar and radiosonde measurements performed during the period from 2000 to 2006. Cirrus clouds are generally observed in a mid-altitude region ranging from 8.6 to 13 km, with mid-cloud temperatures in the range from −65 • to −38 • C. The cloud thickness generally ranges from 1 to 5 km and 38% of the cases studied have thickness between 2 and 3 km. The retrieval of optical depth and lidar ratio of cirrus clouds is performed using three different methods, taking into account multiple scattering effect. The mean optical depth is found to be 0.31±0.24 and the corresponding mean lidar ratio is 30±17 sr following the scheme of Klett-Fernald method. Sub-visual, thin and opaque cirrus clouds are observed at 3%, 57% and 40% of the measured cases, respectively. A comparison of the results obtained between the three methods shows good agreement. The multiple scattering errors of the measured effective extinction coefficients range from 20 to 60%, depending on cloud optical depth. The temperature and thickness dependencies on optical properties have also been studied in detail. A maximum mid-cloud depth of ∼3.5 km is found at temperatures around ∼−47.5 • C, while there is an indication that optical depth and mean extinction coefficient increases with increasing mid-cloud temperature. A correlation between optical depth and thickness was also found. However, no clear dependence of the lidar ratio values on the cloud temperature and thickness was found.

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Section: Introductionmentioning

confidence: 66%

Optical and geometrical characteristics of cirrus clouds over a Southern European lidar station

Giannakaki¹,

Balis²,

Amiridis

et al. 2007

Atmos. Chem. Phys.

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“…It is presumably the ambiguity in classifying a "warm" ice-phase cloud genus, combined with potential questions regarding the representativeness of a single study conducted at a single midlatitude site, which has precluded the adoption of the SC2001 threshold universally within the community with respect to autonomous lidar measurements (though some have applied it; e.g., Cadet et al, 2003). SC2001 acknowledge the latter point, declaring that "cirrus clouds are the product of weather processes such that their occurrence and macrophysical properties will vary significantly over the globe."…”

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confidence: 99%

Distinguishing cirrus cloud presence in autonomous lidar measurements

Campbell

Vaughan

et al. 2015

Atmos. Meas. Tech.

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Abstract. 2012 Level-2 Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite-based cloud data sets are investigated for thresholds that distinguish the presence of cirrus clouds in autonomous lidar measurements, based on temperatures, heights, optical depth and phase. A thermal threshold, proposed by Sassen and Campbell (2001) C, respectively, for tops and bases) and optical depths (1.18 vs. 1.23) reflect the sensitivity to this constraint. Over 99 % of all T top ≤ −37 • C clouds are classified as ice by CALIOP Level-2 algorithms. Over 81 % of all ice clouds correspond with T top ≤ −37 • C. For instruments lacking polarized measurements, and thus practical estimates of phase, T top ≤ −37 • C provides sufficient justification for distinguishing cirrus, as opposed to the risks of glaciated liquid-water cloud contamination occurring in a given sample from clouds identified at relatively "warm" (T top > −37 • C) temperatures. Although accounting for uncertainties in temperatures collocated with lidar data (i.e., model reanalyses/sondes) may justifiably relax the threshold to include warmer cases, the ambiguity of "warm" ice clouds cannot be fully reconciled with available measurements, conspicuously including phase. Cloud top heights and optical depths are investigated, and global distributions and frequencies derived, as functions of CALIOP-retrieved phase. These data provide little additional information, compared with temperature alone, and may exacerbate classification uncertainties overall. MotivationCirrus clouds are recognized by sky gazers for their translucent and fibrous appearance, cast frequently as delicate white filaments across otherwise clear blue skies at relatively high tropospheric altitudes. To climate scientists however, cirrus clouds, which are composed almost exclusively of ice crystals, are distinct for their physical and radiative properties (e.g., Liou, 1986). As cold and optically thin counterparts to most liquid-water and mixed-phase clouds (e.g., Sassen and Cho, 1992), the net column-integrated radiative impact of cirrus cloud presence during sunlit hours varies between positive and negative, depending on the relative magnitudes of their simultaneous and offsetting contributions diurnally to tropospheric warming (infrared absorption and reemission) and cooling (solar albedo effects; Stephens et al., 1990). This attribute makes cirrus relatively unique among cloud genera. Combined with their relatively high occurrence frequencies globally (e.g., Holz et al., 2008), cirrus are significant and distinct contributors to climate overall .Lidars are primary remote-sensing tools used for monitoring cirrus clouds (e.g., Sassen, 1991). Two complementary NASA lidar projects are presently tasked with compiling Published by Copernicus Publications on behalf of the European Geosciences Union.

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“…On average this is equivalent to approximately 30 temperature profiles per month. Réunion and Mauna Loa temperature lidar profiles have been widely used in different research projects (Leblanc et al, 1998(Leblanc et al, , 1999Morel et al, 2002;Cadet et al, 2003;Bencherif et al, 2007;Dou et al, 2009;Sivakumar et al, 2011;.…”

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confidence: 99%

Statistical analysis of the mesospheric inversion layers over two symmetrical tropical sites: Réunion (20.8° S, 55.5° E) and Mauna Loa (19.5° N, 155.6° W)

et al. 2017

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Abstract. In this investigation a statistical analysis of the characteristics of mesospheric inversion layers (MILs) over tropical regions is presented. This study involves the analysis of 16 years of lidar observations recorded at Réunion (20.8° S, 55.5° E) and 21 years of lidar observations recorded at Mauna Loa (19.5° N, 155.6° W) together with SABER observations at these two locations. MILs appear in 10 and 9.3 % of the observed temperature profiles recorded by Rayleigh lidar at Réunion and Mauna Loa, respectively. The parameters defining MILs show a semi-annual cycle over the two selected sites with maxima occurring near the equinoxes and minima occurring during the solstices. Over both sites, the maximum mean amplitude is observed in April and October, and this corresponds to a value greater than 35 K. According to lidar observations, the maximum and minimum mean of the base height ranged from 79 to 80.5 km and from 76 to 77.5 km, respectively. The MILs at Réunion appear on average ∼ 1 km thinner and ∼ 1 km lower, with an amplitude of ∼ 2 K higher than Mauna Loa. Generally, the statistical results for these two tropical locations as presented in this investigation are in fairly good agreement with previous studies. When compared to lidar measurements, on average SABER observations show MILs with greater amplitude, thickness and base altitudes of 4 K, 0.75 and 1.1 km, respectively. Taking into account the temperature error by SABER in the mesosphere, it can therefore be concluded that the measurements obtained from lidar and SABER observations are in significant agreement. The frequency spectrum analysis based on the lidar profiles and the 60-day averaged profile from SABER confirms the presence of the semi-annual oscillation where the magnitude maximum is found to coincide with the height range of the temperature inversion zone. This connection between increases in the semi-annual component close to the inversion zone is in agreement with most previously reported studies over tropics based on satellite observations. Results presented in this study confirm through the use of the ground-based Rayleigh lidar at Réunion and Mauna Loa that the semi-annual oscillation contributes to the formation of MILs over the tropical region.

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A sub‐tropical cirrus clouds climatology from Reunion Island (21°S, 55°E) lidar data set

Cited by 39 publications

References 18 publications

Optical and geometrical characteristics of cirrus clouds over a Southern European lidar station

Optical and geometrical characteristics of cirrus clouds over a Southern European lidar station

Distinguishing cirrus cloud presence in autonomous lidar measurements

Statistical analysis of the mesospheric inversion layers over two symmetrical tropical sites: Réunion (20.8° S, 55.5° E) and Mauna Loa (19.5° N, 155.6° W)

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A sub‐tropical cirrus clouds climatology from Reunion Island (21°S, 55°E) lidar data set

Cited by 39 publications

References 18 publications

Optical and geometrical characteristics of cirrus clouds over a Southern European lidar station

Optical and geometrical characteristics of cirrus clouds over a Southern European lidar station

Distinguishing cirrus cloud presence in autonomous lidar measurements

Statistical analysis of the mesospheric inversion layers over two symmetrical tropical sites: Réunion (20.8° S, 55.5° E) and Mauna Loa (19.5° N, 155.6° W)

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Statistical analysis of the mesospheric inversion layers over two symmetrical tropical sites: Réunion (20.8° S, 55.5° E) and Mauna Loa (19.5° N, 155.6° W)