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A detailed cloud fraction climatology of the Upper Indus Basin and its implications for near surface air temperature

Lookup NU author(s): Dr Nathan Forsythe, Andrew Hardy, Professor Hayley Fowler, Dr Stephen Blenkinsop, Professor Chris Kilsby, David Archer

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Abstract

Clouds play a key role in hydro-climatological variability by modulating the surface energy balance and air temperature. This study utilises MODIS cloud cover data, with corroboration from global meteorological reanalysis (ERA-Interim) cloud estimates, to describe a cloud climatology for the Upper Indus Basin. It has specific focus on tributary catchments in the northwest of the region which contribute a large fraction of basin annual runoff, including 65% of flow originating above Besham, or 50 km3 27 per year in absolute terms. In this region there is substantial cloud cover throughout the year, with spatial means of 50% to 80% depending on the season. The annual cycles of catchment spatial mean day-time and night-time cloud-cover fraction are very similar. This regional diurnal homogeneity belies substantial spatial variability, particularly along seasonally varying vertical profiles (based on surface elevation). Correlations between local near surface air temperature observations and MODIS cloud cover fraction confirm the strong linkages between local atmospheric conditions and near surface climate variability. These correlations are interpreted in terms of seasonal and diurnal variations in apparent cloud radiative effect and its influence on near surface air temperature in the region. The potential role of cloud radiative effect in recognised seasonally and diurnally asymmetrical temperature trends over recent decades is also assessed by relating these locally observed trends to ERA-Interim-derived trends in cloud-cover fraction. Specifically, reduction in night-time cloud cover fraction relative to day-time conditions over recent decades appears to provide a plausible physical mechanism for the observed night-time cooling of surface air temperature in summer months.


Publication metadata

Author(s): Forsythe N, Hardy AJ, Fowler HJ, Blenkinsop S, Kilsby CG, Archer DR, Hashmi MZ

Publication type: Article

Publication status: Published

Journal: Journal of Climate

Year: 2015

Volume: 28

Issue: 9

Pages: 3537-3556

Print publication date: 01/05/2015

Online publication date: 01/05/2015

Acceptance date: 26/01/2015

ISSN (print): 0894-8755

ISSN (electronic): 1520-0442

Publisher: American Meteorological Society

URL: http://dx.doi.org/10.1175/JCLI-D-14-00505.1

DOI: 10.1175/JCLI-D-14-00505.1


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