Tropospheric low‐level temperature inversions in the Canadian Arctic

Kahl, Jonathan D. W.; Serreze, Mark C.; Schnell, R. C.

doi:10.1080/07055900.1992.9649453

Cited by 76 publications

(79 citation statements)

References 21 publications

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“…Even more difficult to detect are low-level water or ice fogs, the most common being ice crystal precipitation in winter and early spring. The problem in their detection is that they usually exist within the low-level temperature inversion (Kahl et al, 1992) and may result in topof-atmosphere radiances very close to what would be observed in their absence; i.e., their radiative properties, both shortwave and longwave, are similar to those of the surface. This often equates to a top-of-atmosphere temperature difference of a few degrees or less.…”

Section: Undetected Cloudsmentioning

confidence: 99%

On the Validation of Satellite-Derived Sea Ice Surface Temperature

Key¹,

Maslanik²,

Papakyriakou

et al. 1994

ARCTIC

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ABSTRACT. The surface temperature of sea ice controls the rate of ice growth and heat exchange between the ocean and the atmosphere. An algorithm for the satellite retrieval of ice surface temperature has recently been published, but due to the lack of validation data has not been extensively tested. In this paper, data from a recent Arctic field experiment is used in an attempt to validate that algorithm. While the procedure is, in principle, straightforward, we demonstrate that validation is complicated by a variety of factors, including incorrectly assumed atmospheric conditions, undetected clouds in the satellite data, spatial and temporal variability in the surface temperature field, and surface and satellite measurement errors. Comparisons between surface temperatures determined from upwelling broadband longwave radiation, spatial measurements of narrow-band radiation, thermocouples buried just below the snow surface, and narrow-band satellite data show differences of 1 to 3˚C. The range in these independent measurements indicates the need for specially designed validation experiments utilizing narrow-band radiometers on aircraft to obtain broad spatial coverage.Key words: ice surface temperature, Arctic climate, sea ice, AVHRR RÉSUMÉ. La température de la surface de la glace de mer contrôle le taux de croissance de la glace et les échanges thermiques entre l'océan et l'atmosphère. Un algorithme d'extraction par satellite de la température de la surface de la glace a récemment été publié, mais n'a pu être mis à l'essai sur une grande échelle, en raison du manque de données de validation. On tente, dans cet article, de valider cet algorithme à l'aide de données provenant d'une expérience de terrain menée récemment dans l'Arctique. Si la procédure est, en principe, simple, on démontre que divers facteurs viennent compliquer cette validation, dont une évaluation incorrecte des conditions atmosphériques, la présence de nuages non détectés dans les données obtenues par satellite, une variabilité spatiale et temporelle dans la température de surface de l'aire expérimentale, et des erreurs dans les mesures prises sur le terrain même et par satellite. Des comparaisons entre les températures de surface déterminées à partir du rayonnement ascendant des ondes longues à large bande, des mesures spatiales du rayonnement à bande étroite, des thermocouples placés juste sous la surface de la neige et des données de satellite dans la bande étroite révèlent des différences allant de 1 à 3 ˚C. La différence qui existe dans ces mesures prises indépendamment montre bien la nécessité de mettre sur pied des expériences de validation conçues à des fins spécifiques, qui utilisent des radiomètres à bande étroite sur les avions en vue d'obtenir une grande couverture spatiale.Mots clés: température de la surface de la glace, climat de l'Arctique, glace de mer, radiomètre perfectionné à très haute résolution Traduit pour la revue Arctic par Nésida Loyer.

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Section: Undetected Cloudsmentioning

confidence: 99%

On the Validation of Satellite-Derived Sea Ice Surface Temperature

Key¹,

Maslanik²,

Papakyriakou

et al. 1994

ARCTIC

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“…Because of the strongly stable near-surface conditions that often occur during Arctic winter to early spring (Kahl, 1992;Curry, 1986), surface fluxes are often considered to have no significant contribution to the cloud's moisture during these seasons; this changes from late spring until October when both open ice-free ocean and melting sea ice expose a vast source of heat and moisture to the relatively cool and dry lower atmosphere (Pinto and Curry, 1995). Analysis of the vertical atmospheric structure in late summer from four different expeditions, including the Arctic Summer Cloud Ocean Study (ASCOS; www.ascos.se, also see Tjernström et al, 2014), revealed a neutrally stratified layer extending from the surface up to about 300-600 m , which indicates that the surface and the boundarylayer clouds could potentially be thermodynamically coupled.…”

Section: Introductionmentioning

confidence: 99%

The thermodynamic structure of summer Arctic stratocumulus and the dynamic coupling to the surface

et al. 2014

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Abstract. The vertical structure of Arctic low-level clouds and Arctic boundary layer is studied, using observations from ASCOS (Arctic Summer Cloud Ocean Study), in the central Arctic, in late summer 2008. Two general types of cloud structures are examined: the "neutrally stratified" and "stably stratified" clouds. Neutrally stratified are mixedphase clouds where radiative-cooling near cloud top produces turbulence that generates a cloud-driven mixed layer. When this layer mixes with the surface-generated turbulence, the cloud layer is coupled to the surface, whereas when such an interaction does not occur, it remains decoupled; the latter state is most frequently observed. The decoupled clouds are usually higher compared to the coupled; differences in thickness or cloud water properties between the two cases are however not found. The surface fluxes are also very similar for both states. The decoupled clouds exhibit a bimodal thermodynamic structure, depending on the depth of the sub-cloud mixed layer (SCML): clouds with shallower SCMLs are disconnected from the surface by weak inversions, whereas those that lay over a deeper SCML are associated with stronger inversions at the decoupling height. Neutrally stratified clouds generally precipitate; the evaporation/sublimation of precipitation often enhances the decoupling state. Finally, stably stratified clouds are usually lower, geometrically and optically thinner, non-precipitating liquidwater clouds, not containing enough liquid to drive efficient mixing through cloud-top cooling.

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“…The position of a cloud in a vertical profile is closely tied to the vertical temperature structure of the atmosphere (Norris, 1998). A temperature inversion in the Arctic is common during all seasons between the surface and altitudes of 1-2 km, which has become known as the "Arctic inversion" Kahl, 1990;Kahl et al, 1992;Serreze et al, 1992;Kahl and Martinez, 1996;Tjernström and Graversen, 2009). Sedlar and Tjernström (2009) show that during late summer only 30 % of cloud tops are coincident with the temperature inversion base, as found in marine stratocumulus at lower latitudes (Paluch and Lenschow, 1991;Stevens et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Modelling atmospheric structure, cloud and their response to CCN in the central Arctic: ASCOS case studies

et al. 2012

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Abstract.Observations made during late summer in the central Arctic Ocean, as part of the Arctic Summer Cloud Ocean Study (ASCOS), are used to evaluate cloud and vertical temperature structure in the Met Office Unified Model (MetUM). The observation period can be split into 5 regimes; the first two regimes had a large number of frontal systems, which were associated with deep cloud. During the remainder of the campaign a layer of low-level cloud occurred, typical of central Arctic summer conditions, along with two periods of greatly reduced cloud cover. The short-range operational NWP forecasts could not accurately reproduce the observed variations in near-surface temperature. A major source of this error was found to be the temperature-dependant surface albedo parameterisation scheme. The model reproduced the low-level cloud layer, though it was too thin, too shallow, and in a boundary-layer that was too frequently well-mixed. The model was also unable to reproduce the observed periods of reduced cloud cover, which were associated with very low cloud condensation nuclei (CCN) concentrations (<1 cm −3 ). As with most global NWP models, the MetUM does not have a prognostic aerosol/cloud scheme but uses a constant CCN concentration of 100 cm −3 over all marine environments. It is therefore unable to represent the low CCN number concentrations and the rapid variations in concentration frequently observed in the central Arctic during late summer. Experiments with a single-column model configuration of the MetUM show that reducing model CCN number concentrations to observed values reduces the amount of cloud, increases the near-surface stability, and improves the representation of both the surface radiation fluxes and the surface temperature. The model is shown to be sensitive to CCN only when number concentrations are less than 10-20 cm −3 .

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Tropospheric low‐level temperature inversions in the Canadian Arctic

Abstract: Climatological characteristics of thé law-level tropospheric température inversion in thé Canadian

Cited by 76 publications

References 21 publications

On the Validation of Satellite-Derived Sea Ice Surface Temperature

On the Validation of Satellite-Derived Sea Ice Surface Temperature

The thermodynamic structure of summer Arctic stratocumulus and the dynamic coupling to the surface

Modelling atmospheric structure, cloud and their response to CCN in the central Arctic: ASCOS case studies

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