Long-term response of daily epilimnetic temperature extrema to climate forcing

Authors: Wilhelm, Susann; Hintze, Thomas; Livingstone, David M; Adrian, Rita

Source: Canadian Journal of Fisheries and Aquatic Sciences, Volume 63, Number 11, November 2006 , pp. 2467-2477(11)

Publisher: NRC Research Press

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Abstract:

Twenty years (1983–2002) of hourly summer temperature data from the epilimnion of Müggelsee, a shallow lake in northern Germany, showed a long-term increase, with the rate of increase of the daily minima (nighttime temperatures) exceeding that of the daily maxima (daytime temperatures). This does not simply reflect the long-term behaviour of air temperature, which did not exhibit a significant degree of day–night asymmetry. A sensitivity analysis based on a heat-balance model revealed that the daily extrema of the lake surface equilibrium temperature responded differently not only to shifts in air temperature, but also to shifts in wind speed, relative humidity, and cloud cover, suggesting that long-term changes in all four variables contribute to day–night asymmetry in the epilimnetic temperature. A comparison of nighttime and daytime estimates of the heat flux components into the lake indicates that the emission of long-wave radiation from the atmosphere is likely to be the main process responsible for day–night asymmetry in the epilimnetic temperature. Although this process is partially dependent on air temperature, it is also dependent on relative humidity and cloud cover. The influence of long-term changes in these additional driving variables on epilimnetic temperatures cannot therefore be neglected.

Des séries horaires de données de température d'été sur 20 ans (1983–2002) dans l'épilimnion de Müggelsee, un lac peu profond du nord de l'Allemagne, montrent une augmentation à long terme de la température, dont le taux d'accroissement des minimums journaliers (températures nocturnes) surpasse celui des maximums journaliers (températures diurnes). Cela ne reflète pas simplement le comportement à long terme de la température de l'air, qui ne montre pas un degré significatif d'asymétrie jour–nuit. Une analyse de sensibilité basée sur un modèle de bilan thermique indique que les extrêmes journaliers de l'équilibre thermique à la surface du lac réagissent différemment non seulement aux changements de température de l'air, mais aussi aux changements de vitesse du vent, d'humidité relative et de couverture nuageuse; cela laisse croire que des changements à long terme de ces quatre variables contribuent à l'asymétrie jour–nuit de la température de l'épilimnion. Une comparaison des estimations des composantes du flux thermique dans le lac durant le jour et durant la nuit indique que l'émission de radiation à grande longueur d'onde dans l'atmosphère est vraisemblablement le processus principal responsable de l'asymétrie de la température de l'épilimnion. Bien que ce processus soit partiellement dépendant de la température de l'air, il est aussi dépendant de l'humidité relative et de la couverture nuageuse. L'influence des changements à long terme de ces variables explicatives additionnelles ne peut donc pas être négligée.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: November 1, 2006

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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