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Stratiform Cloud—Inversion Characterization During the Arctic Melt Season
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
2009 (English)In: Boundary-layer Meteorology, ISSN 0006-8314, E-ISSN 1573-1472, Vol. 132, no 3, 455-474 p.Article in journal (Refereed) Published
Abstract [en]

Data collected during July and August from the Arctic Ocean Experiment 2001illustrated a common occurrence of specific-humidity (q) inversions, where moistureincreases with height, coinciding with temperature inversions in the central Arctic boundarylayer and lower troposphere. Low-level stratiform clouds and their relationship to temperatureinversions are examined using radiosonde data and data from a suite of remote sensinginstrumentation. Two low-level cloud regimes are identified: the canonical case of stratiformclouds, where the cloud tops are capped by the temperature inversion base (CCI—CloudsCapped by Inversion) and clouds where the cloud tops were found well inside the inversion(CII—Clouds Inside Inversion). The latter case was found to occur more than twiceas frequently than the former. The characteristic of the temperature inversion is shown tohave an influence on the cloud regime that was supported. Statistical analyses of the cloudregimes using remote sensing instruments suggest that CCI cases tend to be dominated bysingle-phase liquid cloud droplets; radiative cooling at the cloud top limits the vertical extentof such clouds to the inversion base height. The CII cases, on the other hand, display characteristicsthat can be divided into two situations—(1) clouds that only slightly penetrate thetemperature inversion and exhibit a microphysical signal similar to CCI cases, or (2) cloudsthat extend higher into the inversion and show evidence of a mixed-phase cloud structure.An important interplay between the mixed-phase structure and an increased potential for turbulentmixing across the inversion base appears to support the lifetime of CII cases existingwithin the inversion layer.

Place, publisher, year, edition, pages
2009. Vol. 132, no 3, 455-474 p.
Keyword [en]
Arctic Clouds
National Category
Meteorology and Atmospheric Sciences
URN: urn:nbn:se:su:diva-32472DOI: 10.1007/s10546-009-9407-1ISI: 000270129600006OAI: diva2:280628
Available from: 2009-12-10 Created: 2009-12-10 Last updated: 2010-11-05Bibliographically approved
In thesis
1. Arctic clouds - interactions with radiation and thermodynamic structure
Open this publication in new window or tab >>Arctic clouds - interactions with radiation and thermodynamic structure
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Clouds play in important role in the climate system through their interaction with radiation. Globally, clouds tend to cool the Earth by reflecting solar radiation and shading the surface. Over the Arctic, clouds tend to have the opposite impact, where they instead warm the surface through the cloud greenhouse effect because the surface is generally quite reflective. The magnitude and overall effect of clouds on the surface varies significantly with the surface, cloud and thermodynamic characteristics and can have large impacts on the energy budget at the surface.

Low-level central-Arctic stratus clouds interact with the thermodynamics in a manner differently than sub-tropical stratus. Observations from several Arctic observatories indicate that these clouds penetrate and persist within stable temperature inversion structures, rather than being limited to the base of the stable layer as observed in the subtropics. It is hypothesized that such interactions with the thermodynamics can impact for example the cloud phase, lifetime, and their relationship with the sub-cloud layer and surface. Analysis indicates both the thermodynamic setting and the cloud properties affect the vertical location of the cloud top relative to inversion base. Hypothetical longwave radiative impacts resulting from liquid water redistributions are identified and discussed.

Clouds primarily influence the energy at the surface via interactions with radiation. Measurements from the central Arctic suggest that the transition of season from melting to freezing was largely determined by the presence, or absence, of liquid-containing clouds and the incumbent cloud longwave warming effect. The components affecting the cloud-radiative forcing are described with relation to the energy budget and the change of season. Additionally, the influence of altering cloud condensation nuclei as a mechanism for limiting cloud liquid water is shown to have strong influences on surface temperature and lower atmospheric stability.

Finally, regional climate models, RCMs, are evaluated against an annual dataset to assess the ability of RCMs to represent cloud and radiation processes in the Arctic. It is shown that both inter-model and model-observation spread are rather significant. Biases in the cloud representations yield distinct biases in the radiative fluxes, and can result in significant local climate variations solely through these parameters.

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University, 2010. 46 p.
Arctic, stratus, radiation, thermodynamic structure, cloud radiative forcing, seasonal transition
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences
urn:nbn:se:su:diva-43935 (URN)978-91-7447-176-2 (ISBN)
Public defence
2010-12-03, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Accepted. Paper 4: Manuscript published in Atmospheric Chemistry and Physics Discussions.Available from: 2010-11-11 Created: 2010-11-01 Last updated: 2010-11-11Bibliographically approved

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