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Signatures of midsummer droughts over Central America and Mexico


Zhao, Z and Han, M and Yang, K and Holbrook, NJ, Signatures of midsummer droughts over Central America and Mexico, Climate Dynamics pp. 1-20. ISSN 0930-7575 (2022) [Refereed Article]

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Copyright (2022) The Author(s). This article is licensed under a Creative Commons Attribution 4.0 International License,, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made.

DOI: doi:10.1007/s00382-022-06505-9


The annual cycle of precipitation over most parts of Central America and southern Mexico is climatologically characterized by a robust bimodal distribution, normally termed as the midsummer drought (MSD), influencing a large range of agricultural economic and public insurances. Compared to studies focusing on mechanisms underpinning the MSD, less research has been undertaken related to its climatological signatures. This is due to a lack of generally accepted methods through which to detect and quantify the bimodal precipitation accurately. The present study focuses on characterizing the MSD climatological signatures over Central America and Mexico using daily precipitation observations between 1979 and 2017, aiming to provide a comprehensive analysis of MSD in fine scale over this region. This was completed using a new method of detection. The signatures were analyzed from three aspects, namely (1) climatological mean states and variability; (2) connections with large scale modes of climate variability (El Nińo–Southern Oscillation (ENSO) and the Madden–Julian Oscillation (MJO)); and (3) the potential afforded by statistical modelling. The development of MSDs across the region is attributed to changes of surface wind–pressure composites, characterized by anomalously negative (positive) surface pressure and onshore (offshore) winds during the peak (trough) of precipitation. ENSO’s modulation of MSDs is also shown by modifying the surface wind–pressure patterns through MSD periods, inducing the intensified North Atlantic Subtropical High and associated easterlies from the Caribbean region, which induce relatively weak precipitation at corresponding time points and subsequently intensify the MSD magnitude and extend the MSD period. Building on previous research which showed MSDs tend to start/end in MJO phases 1 and 8, a fourth–order polynomial was used here to statistically model the precipitation time series during the rainy season. We show that the strength of the bimodal precipitation can be well modelled by the coefficient of the polynomial terms, and the intra-seasonal variability is largely covered by the MJO indices. Using two complete MJO cycles and the polynomial, the bimodal precipitation during the rainy season over Central America and Mexico is synoptically explained, largely contributing to our understanding of the MJO’s modulation on the MSD.

Item Details

Item Type:Refereed Article
Keywords:Central America, El Nińo–Southern oscillation, Madden–Julian oscillation, Mexico, midsummer drought, statistical modelling
Research Division:Earth Sciences
Research Group:Oceanography
Research Field:Physical oceanography
Objective Division:Environmental Policy, Climate Change and Natural Hazards
Objective Group:Understanding climate change
Objective Field:Understanding climate change not elsewhere classified
UTAS Author:Han, M (Ms Meng Han)
UTAS Author:Yang, K (Mr Kai Yang)
UTAS Author:Holbrook, NJ (Professor Neil Holbrook)
ID Code:154034
Year Published:2022
Web of Science® Times Cited:2
Deposited By:Oceans and Cryosphere
Deposited On:2022-10-25
Last Modified:2022-11-03
Downloads:2 View Download Statistics

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