The diurnal cycle of the clouds extending above the tropical tropopause observed by spaceborne lidar

Dauhut, Thibaut; Noël, Vincent; Dion, Iris-Amata

doi:10.5194/acp-20-3921-2020

Cited by 10 publications

(19 citation statements)

References 39 publications

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“…Finally, the absolute difference of 2.6 pp between daytime and nighttime occurrence frequencies derived from CATS is valid for JJA, whereas the 1 pp difference between MIPAS daytime and nighttime occurrence frequencies is valid for the all year mean. A recent study on stratospheric cirrus cloud occurrences in the tropics derived from CATS measurements reports differences of about 3 to 10 pp in DJF and 5 to 7 pp in JJA between 10 am and 10 pm Dauhut et al (2020). This differs from our results that show only 1 pp difference between 10 am and 10 pm measurements.…”

Section: Diurnal Cycle Of Cloud Top Height Occurrencescontrasting

confidence: 99%

“…Although Noel et al (2018) noted that CATS daytime measurements have to be averaged over 60 km to achieve a comparable detection sensitivity as the nighttime measurements averaged over 5 km, the results by Dauhut et al (2020) were derived from 5 km along track averages at daytime and nighttime. The detection sensitivity of CATS measurements averaged over 5 km 16…”

Section: Diurnal Cycle Of Cloud Top Height Occurrencesmentioning

confidence: 99%

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Revisiting global satellite observations of stratospheric cirrus clouds

Zou¹,

Grießbach²,

Hoffmann³

et al. 2020

Preprint

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Abstract. As knowledge about the cirrus clouds in the lower stratosphere is limited, reliable long-term measurements are needed to assess their characteristics, radiative impact and important role in upper troposphere and lower stratosphere (UTLS) chemistry. To investigate the global and seasonal distribution of stratospheric cirrus clouds, we used the latest version (V4.x) of the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) data. For the identification of stratospheric cirrus clouds, precise information on both, the cloud top height (CTH) and the tropopause height is crucial. Here, we used lapse rate tropopause heights estimated from the ERA-Interim global reanalysis. Considering the uncertainties of the tropopause heights and the vertical sampling grid of the CALIPSO data, we considered cirrus clouds with CTHs more than 0.5 km above the tropopause as being stratospheric. We focused on nighttime CALIPSO measurements, because of their higher detection sensitivity. A six-year mean (2006–2012) global distribution of stratospheric cirrus cloud from CALIPSO showed that higher CTH occurrence frequencies are observed in the tropics than in the extra-tropics. Tropical hotspots of stratospheric cirrus clouds associated with deep convection are located over Equatorial Africa, South and Southeast Asia, the western Pacific and South America. Stratospheric cirrus clouds were more often detected in December–February (15 %) than June–August (8 %) in the tropics (± 20°). At middle (40–60°) and higher latitudes (> 60°), CALIPSO observed on average about 2 % stratospheric cirrus clouds. Observations of stratospheric cirrus cloud with MIPAS are presented here for the first time. Taking into account the MIPAS vertical sampling and broad field of view, we considered cirrus CTHs detected not less than 0.75 km above the tropopause as being stratospheric. Compared to CALIPSO, MIPAS observed twice as many stratospheric cirrus clouds at northern and southern middle latitudes (occurrence frequencies of 4–5 % for MIPAS rather than about 2 % for CALIPSO). We attribute more frequent observations of stratospheric cirrus clouds with MIPAS to higher detection sensitivity of the instrument to optically thin clouds. Sensitivity tests on MIPAS stratospheric cloud detections have been conducted to rule out sampling artefacts. Future work should focus on better understanding the origin of the stratospheric cirrus clouds and their impact on radiative forcing and climate.

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Section: Diurnal Cycle Of Cloud Top Height Occurrencescontrasting

confidence: 99%

Section: Diurnal Cycle Of Cloud Top Height Occurrencesmentioning

confidence: 99%

Revisiting global satellite observations of stratospheric cirrus clouds

Zou¹,

Grießbach²,

Hoffmann³

et al. 2020

Preprint

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show abstract

“…Studies found a 96.3 % estimation accuracy of the CALIOP sensor for characterizing the cloud cover compared with the Moderate Resolution Imaging Spectroradiometer (MODIS) and CloudSat Cloud Profiling Radar (CPR) (Chan and Comiso, 2013). CALIPSO is suitable for high-altitude cirrus cloud detection (Davis et al, 2010). The vertical feature mask data (CAL_LID_L2_VFMStandard-V4) used in this study were generated with a new set of cloud-aerosol discrimination (CAD) probability distribution functions.…”

Section: Calipsomentioning

confidence: 99%

“…De Reus et al, 2009). However, for sub-visual cirrus clouds, CALIPSO was estimated to miss up to 66 % of them (Davis et al, 2010). An analysis of cloud occurrence frequencies of 3 years of Optical Spectrograph and InfraRed Imager System (OSIRIS) measurements showed that in the tropics on average about 13 % of the clouds between 12 and 25 km have an optical thickness below 5 × 10 −3 (Bourassa , 2005).…”

Section: Stratospheric Cirrus Cloudsmentioning

confidence: 99%

Revisiting global satellite observations of stratospheric cirrus clouds

Zou

Grießbach²,

Hoffmann³

et al. 2020

Atmos. Chem. Phys.

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Abstract. As knowledge about the cirrus clouds in the lower stratosphere is limited, reliable long-term measurements are needed to assess their characteristics, radiative impact and important role in upper troposphere and lower stratosphere (UTLS) chemistry. We used 6 years (2006–2012) of Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) measurements to investigate the global and seasonal distribution of stratospheric cirrus clouds and compared the MIPAS results with results derived from the latest version (V4.x) of the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) data. For the identification of stratospheric cirrus clouds, precise information on both the cloud top height (CTH) and the tropopause height is crucial. Here, we used lapse rate tropopause heights estimated from the ERA-Interim global reanalysis. Considering the uncertainties of the tropopause heights and the vertical sampling grid, we define CTHs more than 0.5 km above the tropopause as stratospheric for CALIPSO data. For MIPAS data, we took into account the coarser vertical sampling grid and the broad field of view so that we considered cirrus CTHs detected more than 0.75 km above the tropopause as stratospheric. Further sensitivity tests were conducted to rule out sampling artefacts in MIPAS data. The global distribution of stratospheric cirrus clouds was derived from night-time measurements because of the higher detection sensitivity of CALIPSO. In both data sets, MIPAS and CALIPSO, the stratospheric cirrus cloud occurrence frequencies are significantly higher in the tropics than in the extra-tropics. Tropical hotspots of stratospheric cirrus clouds associated with deep convection are located over equatorial Africa, South and Southeast Asia, the western Pacific, and South America. Stratospheric cirrus clouds were more often detected in December–February (15 %) than June–August (8 %) in the tropics (±20∘). At northern and southern middle latitudes (40–60∘), MIPAS observed about twice as many stratospheric cirrus clouds (occurrence frequencies of 4 %–5 % for MIPAS rather than about 2 % for CALIPSO). We attribute more frequent observations of stratospheric cirrus clouds with MIPAS to the higher detection sensitivity of the instrument to optically thin clouds. In contrast to the difference between daytime and night-time occurrence frequencies of stratospheric cirrus clouds by a factor of about 2 in zonal means in the tropics (4 % and 10 %, respectively) and at middle latitudes for CALIPSO data, there is little diurnal cycle in MIPAS data, in which the difference of occurrence frequencies in the tropics is about 1 percentage point in zonal mean and about 0.5 percentage point at middle latitudes. The difference between CALIPSO day and night measurements can also be attributed to their differences in detection sensitivity. Future work should focus on better understanding the origin of the stratospheric cirrus clouds and their impact on radiative forcing and climate.

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“…Thus, CATS is expected to provide important complementary and new information on clouds, including high clouds in the tropics. The first studies using CATS have recently been realized, and provided new insights into the diurnally resolved cloud occurrence [10]; the interplay of humidity, convection, and clouds in the tropics [11]; and the occurrence and characteristics of stratospheric overshoot in the tropics [12]. While some first validation of CATS level 2 observations (geophysical parameters and optical properties, like cloud detection or optical depth) has been provided, e.g., with ground-based instruments [10], further validation efforts would be beneficial for gaining more confidence in these first results.…”

Section: Introductionmentioning

confidence: 99%

Comparison of ISS–CATS and CALIPSO–CALIOP Characterization of High Clouds in the Tropics

2020

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Clouds in the tropics have an important role in the energy budget, atmospheric circulation, humidity, and composition of the tropical-to-global upper-troposphere–lower-stratosphere. Due to its non-sun-synchronous orbit, the Cloud–Aerosol Transport System (CATS) onboard the International Space Station (ISS) provided novel information on clouds from space in terms of overpass time in the period of 2015–2017. In this paper, we provide a seasonally resolved comparison of CATS characterization of high clouds (between 13 and 18 km altitude) in the tropics with well-established CALIPSO (Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation) data, both in terms of clouds’ occurrence and cloud optical properties (optical depth). Despite the fact that cloud statistics for CATS and CALIOP are generated using intrinsically different local overpass times, the characterization of high clouds occurrence and optical properties in the tropics with the two instruments is very similar. Observations from CATS underestimate clouds occurrence (up to 80%, at 18 km) and overestimate the occurrence of very thick clouds (up to 100% for optically very thick clouds, at 18 km) at higher altitudes. Thus, the description of stratospheric overshoots with CATS and CALIOP might be different. While this study hints at the consistency of CATS and CALIOP clouds characterizaton, the small differences highlighted in this work should be taken into account when using CATS for estimating cloud properties and their variability in the tropics.

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The diurnal cycle of the clouds extending above the tropical tropopause observed by spaceborne lidar

Cited by 10 publications

References 39 publications

Revisiting global satellite observations of stratospheric cirrus clouds

Revisiting global satellite observations of stratospheric cirrus clouds

Revisiting global satellite observations of stratospheric cirrus clouds

Comparison of ISS–CATS and CALIPSO–CALIOP Characterization of High Clouds in the Tropics

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