The vertical distribution of thin features over the Arctic analysed from CALIPSO observations. Part I: Optically thin clouds

Devasthale, Abhay; Tjernström, Michael; Karlsson, Karl-Göran; Thomas, Manu Anna; Jones, Colin; Sedlar, Joseph; Omar, Ali

doi:10.3402/tellusb.v63i1.16189

Cited by 10 publications

(11 citation statements)

References 38 publications

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“…Annual arctic cloud fractions are high [e.g., Shupe et al , 2011; Devasthale et al , 2011b], however clear‐sky conditions do occur (Figure 2a). Mean monthly clear‐sky fraction for the box region peaks near 65% during the end of winter and approaches a summer minimum near 10% in August.…”

Section: Resultsmentioning

confidence: 99%

Clear‐sky thermodynamic and radiative anomalies over a sea ice sensitive region of the Arctic

Sedlar

Devasthale

2012

J. Geophys. Res.

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Estimates of mean greenhouse anomalies indicate a shift from negative to positive anomalies midway through the 8-year record. Sensitivity tests suggest that temperature anomalies are the strongest contributor to both LWD and greenhouse anomalies, relative to water-vapor anomalies; monthly averaging of column precipitable water yields relatively small anomalies (order 1 mm) that produce a linear response in greenhouse anomalies. Finally the clear-sky contribution to 2007 monthly ice thickness is estimated. Anomalous clear-sky radiation retards the total 2007 ice thickness by 0.3 m (15-30% of ice-thickness climatology), and anomalous LW radiation is most important for preconditioning the ice during the months prior to, and after, the summer melt season. A highly sensitive interaction between cloud fraction, surface albedo and LWD anomalies is found, and we develop a metric for determining clear-sky anomalous ice melt potential.Citation: Sedlar, J., and A. Devasthale (2012), Clear-sky thermodynamic and radiative anomalies over a sea ice sensitive region of the Arctic,

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Section: Resultsmentioning

confidence: 99%

Clear‐sky thermodynamic and radiative anomalies over a sea ice sensitive region of the Arctic

Sedlar

Devasthale

2012

J. Geophys. Res.

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“…In the Surface Heat Budget of the Arctic Ocean (SHEBA), the majority of clouds (.50%) are within the lowermost 1 km of the troposphere and show a distinct bimodal seasonal cycle, whereas in Eureka less than 30%-40% of all clouds are below the lowerest kilometer. Using CALIPSO data covering nearly the entire Arctic, Devasthale et al (2011) show that roughly 35% of all thin water clouds are observed below 800 m in spring and about 25% in other seasons. It is, however, to be noted that even if CloudSat cannot fully sample all cloud regimes over the Arctic, these clouds remain highly susceptible to the assumptions regarding the temperature range and the relationship shape (as shown later in the present study) because of their mixed-phase nature (Shupe 2011).…”

Section: The Cloudsat Datasetsmentioning

confidence: 98%

Sensitivity of Cloud Liquid Water Content Estimates to the Temperature-Dependent Thermodynamic Phase: A Global Study Using CloudSat Data

Devasthale

Thomas

2012

Journal of Climate

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The main purpose of this study is to underline the sensitivity of cloud liquid water content (LWC) estimates purely to 1) the shape of computationally simplified temperature-dependent thermodynamic phase and 2) the range of subzero temperatures covered to partition total cloud condensate into liquid and ice fractions. Linear, quadratic, or sigmoid-shaped functions for subfreezing temperatures (down to 2208 or 2408C) are often used in climate models and reanalysis datasets for partitioning total condensate. The global vertical profiles of clouds obtained from CloudSat for the 4-yr period June 2006-May 2010 are used for sensitivity analysis and the quantitative estimates of sensitivities based on these realistic cloud profiles are provided. It is found that three cloud regimes in particular-convective clouds in the tropics, low-level clouds in the northern high latitudes, and middle-level clouds over the midlatitudes and Southern Ocean-are most sensitive to assumptions on thermodynamic phase. In these clouds, the LWC estimates based purely on quadratic or sigmoid-shaped functions with a temperature range down to 2208C can differ by up to 20%-40% over the tropics (in seasonal means), 10%-30% over the midlatitudes, and up to 50% over high latitudes compared to a linear assumption. When the temperature range is extended down to 2408C, LWC estimates in the sigmoid case can be much higher than the above values over high-latitude regions compared to the commonly used case with quadratic dependency down to 2208C. This sensitivity study emphasizes the need to critically investigate radiative impacts of cloud thermodynamic phase assumptions in simplified climate models and reanalysis datasets.

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“…The spatial pattern of the number of clearsky observations is different in different seasons mainly governed by the seasonality in the cloud fraction. The cloud fraction is at a minimum (maximum) in winter (summer) (Curry et al, 1996;Devasthale et al, 2011;Shupe et al, 2011). Therefore, the total numbers of clear-sky observations are highest (lowest) during winter (summer).…”

Section: The Airs Datasetmentioning

confidence: 99%

Characteristics of water-vapour inversions observed over the Arctic by Atmospheric Infrared Sounder (AIRS) and radiosondes

2011

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Abstract. An accurate characterization of the vertical structure of the Arctic atmosphere is useful in climate change and attribution studies as well as for the climate modelling community to improve projections of future climate over this highly sensitive region. Here, we investigate one of the dominant features of the vertical structure of the Arctic atmosphere, i.e. water-vapour inversions, using eight years of Atmospheric Infrared Sounder data (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010) and radiosounding profiles released from the two Arctic locations (North Slope of Alaska at Barrow and during SHEBA). We quantify the characteristics of clear-sky water vapour inversions in terms of their frequency of occurrence, strength and height covering the entire Arctic for the first time.We found that the frequency of occurrence of watervapour inversions is highest during winter and lowest during summer. The inversion strength is, however, higher during summer. The observed peaks in the median inversionlayer heights are higher during the winter half of the year, at around 850 hPa over most of the Arctic Ocean, Siberia and the Canadian Archipelago, while being around 925 hPa during most of the summer half of the year over the Arctic Ocean. The radiosounding profiles agree with the frequency, location and strength of water-vapour inversions in the Pacific sector of the Arctic. In addition, the radiosoundings indicate that multiple inversions are the norm with relatively few cases without inversions. The amount of precipitable water within the water-vapour inversion structures is estimated and we find a distinct, two-mode contribution to the total column precipitable water. These results suggest that water-vapour inversions are a significant source to the column thermodynamics, especially during the colder winCorrespondence to: A. Devasthale (abhay.devasthale@smhi.se) ter and spring seasons. We argue that these inversions are a robust metric to test the reproducibility of thermodynamics within climate models. An accurate statistical representation of water-vapour inversions in models would mean that the large-scale coupling of moisture transport, precipitation, temperature and water-vapour vertical structure and radiation are essentially captured well in such models.

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The vertical distribution of thin features over the Arctic analysed from CALIPSO observations. Part I: Optically thin clouds

Cited by 10 publications

References 38 publications

Clear‐sky thermodynamic and radiative anomalies over a sea ice sensitive region of the Arctic

Clear‐sky thermodynamic and radiative anomalies over a sea ice sensitive region of the Arctic

Sensitivity of Cloud Liquid Water Content Estimates to the Temperature-Dependent Thermodynamic Phase: A Global Study Using CloudSat Data

Characteristics of water-vapour inversions observed over the Arctic by Atmospheric Infrared Sounder (AIRS) and radiosondes

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