The stationarity of global mean climate

Hunt, B. G.

doi:10.1002/joc.1016

Cited by 22 publications

(9 citation statements)

References 16 publications

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“…The basic patterns shown in Figure 1 were stable across individual millennia of the simulation, although with reduced frequencies of occurrence. This outcome is consistent with the stationarity of the replicated climate discussed by Hunt (2004). The occurrence rates for the individual gridboxes shown in Figure 1 can be assessed against the rates to be expected by chance.…”

Section: Spatial Patternssupporting

confidence: 83%

“…This is a necessary consequence of the lack of any external forcing, but is only attainable if there is no drift within the simulation; this is the case for this particular simulation. Time series of basic variables such as surface temperature, cloud amount and rainfall were constant within 1-2% over the 10 000 years of the simulations, as are the limited observations (Hunt, 2004). At the regional or local level climatic time series were also stationary, while exhibiting noticeable interannual variability.…”

Section: Model Description and Experimental Detailsmentioning

confidence: 81%

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Global characteristics of pluvial and dry multi‐year episodes, with emphasis on megadroughts

Hunt

2011

Intl Journal of Climatology

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A multi-millenial simulation with a coupled atmospheric-oceanic climatic model has been used to investigate the occurrence rate and characteristics of multi-year dry and pluvial episodes. Such episodes are defined as having the same sign rainfall anomalies for the whole of their durations. Episodes of 5-, 8-and 10-year durations are shown to occur all over the globe. The occurrence rates are approximately in agreement with probabilistic expectations, although there are spatial variations associated with El Nino Southern Oscillation (ENSO) influences. The impacts of the dry and pluvial episodes are considerable, with 10-year duration dry episodes resulting in a loss of at least one year's rainfall over the oceans and much larger losses over arid regions. Similar but positive outcomes are associated with pluvial episodes. Accumulated rainfall anomalies over various multi-decadal periods indicate that regions with persistent features can occur, implying longer term impacts than might have been expected from a succession of dry and pluvial episodes. Time series of these episodes for individual model gridboxes highlight a disparity between the occurrence rates of dry and pluvial episodes and the lack of synchronicity of these episodes at the various gridboxes. These time series also clearly illustrate the rapid fall-off in the occurrence rates of the episodes as their durations are increased. Despite claims in the literature that 'megadroughts' are typically associated with extended ENSO events, it is shown that for a very extended La Nina event the rainfall anomalies in a number of ENSO-sensitive regions experienced interannual variability rather than a persistent anomaly. The role of a number of large-scale oscillations in generating rainfall anomalies is examined, but it is concluded that stochastic processes are needed to account for the extended duration of dry and pluvial episodes, in addition to any forcing associated with such oscillations. This adds a random aspect to the determination of whether any given, say, ENSO event will become a dry or pluvial episode.

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Section: Spatial Patternssupporting

confidence: 83%

Section: Model Description and Experimental Detailsmentioning

confidence: 81%

Global characteristics of pluvial and dry multi‐year episodes, with emphasis on megadroughts

Hunt

2011

Intl Journal of Climatology

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“…This is most easily exemplified by consideration of the meridional wind distribution. Figure 6a illustrates the annual mean surface meridional wind distribution for year 7375 (this pattern is essentially invariant with time for the contour intervals used in the figure (see Hunt, 2004)). The important features of this figure as regards the present study are the large, topographically-constrained wind maxima off the west and east coasts of the Americas.…”

Section: Simulated Yucatan Climatologymentioning

confidence: 98%

A Simulation of the Climatic Conditions Associated with the Collapse of the Maya Civilization

Hunt

Elliott

2005

Climatic Change

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It has been speculated that the collapse of the Maya civilization in the Yucatan region of Mexico around 900 AD was caused by drought. A 10,000-year simulation with the CSIRO Mark 2 coupled global climatic model has been used to investigate such a possibility. The model replicates sporadic, severe drought over the Yucatan consistent with the above speculation. It was found that these droughts were specifically constrained to the Central American area, with no obvious linkages to other regions. An investigation of the mechanisms associated with rainfall fluctuations over the Yucatan indicates that these were not caused by sea surface temperature variations. Fluctuations in the intensity of the topographically constrained meridional wind systems located on both the western and eastern coasts of the Americas were found to be the dominant influence. The sensitivity of the Yucatan to drought episodes arises from its location at the convergence zone of these wind systems. It is concluded that the severe drought episodes in this region are a consequence of stochastic fluctuations of these wind systems and that external influences are not necessary.

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“…Model outputs were stored at monthly intervals, as means or accumulations, for a wide range of atmospheric, sea-ice and oceanic variables. The model did not experience any climatic drift during the 10 000-year run; annual mean, globally averaged individual climatic variables were time-invariant to within 1-2% (see Hunt (2004) for an analysis of this aspect of the simulation).…”

Section: Model Descriptionmentioning

confidence: 99%

Climatic outliers

Hunt¹

2006

Intl Journal of Climatology

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Abstract:A 10 000-year simulation for 'present' climate has been generated with the CSIRO Mark 2 coupled climatic model. In this paper the model output has been analysed to produce a climatology of climatic outliers and to assess the role of such outliers in climatic variability. An assessment of the frequency of occurrence of outliers, compared with the statistical expectation from a Gaussian distribution, indicates that over most of the globe the surface temperature conforms to this distribution, but this is not the case for rainfall. Among the issues considered are the spatial occurrence rates over the globe of normalised climatic anomalies of various magnitudes, the temporal variability of outliers, the seasonal variability for a given outlier year, the spatial characteristics of outliers and the question of precursors to outliers. The relationship of outliers to the El Niño/Southern Oscillation, the Pacific Decadal Oscillation and the North Atlantic Oscillation is also considered. A case study examining the relative severities of an outlier drought to a severe drought is also undertaken. Finally, the role of outliers and the greenhouse effect is considered. It is concluded that outliers are a manifestation of stochastic forcing.

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The stationarity of global mean climate

Cited by 22 publications

References 16 publications

Global characteristics of pluvial and dry multi‐year episodes, with emphasis on megadroughts

Global characteristics of pluvial and dry multi‐year episodes, with emphasis on megadroughts

A Simulation of the Climatic Conditions Associated with the Collapse of the Maya Civilization

Climatic outliers

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