Editorial Type:
Article
Article Type:
Research Article

Spatiotemporal Variability and Predictability of Relative Humidity over West African Monsoon Region

Daniel Broman Civil, Environmental, and Architectural Engineering, University of Colorado, Boulder, Colorado

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Balaji Rajagopalan Civil, Environmental, and Architectural Engineering, and CIRES, University of Colorado, Boulder, Colorado

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Thomas Hopson National Center for Atmospheric Research, Boulder, Colorado

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Print Publication:
15 Jul 2014
DOI:
https://doi.org/10.1175/JCLI-D-13-00414.1
Page(s):
5346–5363
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Abstract

Spatial and temporal variability of relative humidity over the West African monsoon (WAM) region is investigated. In particular, the variability during the onset and retreat periods of the monsoon is considered. A K-means cluster analysis was performed to identify spatially coherent regions of relative humidity variability during the two periods. The cluster average of the relative humidity provides a robust representative index of the strength and timing of the transition periods between the dry and wet periods. Correlating the cluster indices with large-scale circulation and sea surface temperatures indicates that the land–ocean temperature gradient and the corresponding circulation, tropical Atlantic sea surface temperatures (SSTs), and to a somewhat lesser extent tropical Pacific SSTs all play a role in modulating the timing of the monsoon season relative humidity onset and retreat. These connections to large-scale climate features were also found to be persistent over interseasonal time scales, and thus best linear predictive models were developed to enable skillful forecasts of relative humidity during the two periods at 15–75-day lead times. The public health risks due to meningitis epidemics are of grave concern to the population in this region, and these risks are strongly tied to regional humidity levels. Because of this linkage, the understanding and predictability of relative humidity variability is of use in meningitis epidemic risk mitigation, which motivated this research.

Corresponding author address: Thomas Hopson, Hydrologic Applications Program, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307-3000. E-mail: hopson@ucar.edu

Abstract

Spatial and temporal variability of relative humidity over the West African monsoon (WAM) region is investigated. In particular, the variability during the onset and retreat periods of the monsoon is considered. A K-means cluster analysis was performed to identify spatially coherent regions of relative humidity variability during the two periods. The cluster average of the relative humidity provides a robust representative index of the strength and timing of the transition periods between the dry and wet periods. Correlating the cluster indices with large-scale circulation and sea surface temperatures indicates that the land–ocean temperature gradient and the corresponding circulation, tropical Atlantic sea surface temperatures (SSTs), and to a somewhat lesser extent tropical Pacific SSTs all play a role in modulating the timing of the monsoon season relative humidity onset and retreat. These connections to large-scale climate features were also found to be persistent over interseasonal time scales, and thus best linear predictive models were developed to enable skillful forecasts of relative humidity during the two periods at 15–75-day lead times. The public health risks due to meningitis epidemics are of grave concern to the population in this region, and these risks are strongly tied to regional humidity levels. Because of this linkage, the understanding and predictability of relative humidity variability is of use in meningitis epidemic risk mitigation, which motivated this research.

Corresponding author address: Thomas Hopson, Hydrologic Applications Program, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307-3000. E-mail: hopson@ucar.edu
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