Austral Summer Droughts and their Driving Mechanisms in Observations and Present-day Climate Simulations across Malawi

2021 ◽  
Author(s):  
Emmanuel Likoya ◽  
Cathryn Birch ◽  
Sarah Chapman ◽  
Andrew Dougill
Keyword(s):  
Atmospheric Circulation ◽  
Climate Models ◽  
Moisture Flux ◽  
Development Planning ◽  
Global Climate Models ◽  
Cmip5 Models ◽  
Atmospheric Circulation Patterns ◽  
Societal Relevance ◽  
Circulation Patterns ◽  
Moisture Fluxes

<p>The societal relevance of droughts in Africa underscores the need for improved understanding of the atmospheric processes that drive them. This study examined drought characteristics across Malawi, and the associated atmospheric circulation patterns, in observations, reanalysis and global climate models. Droughts were identified using the Standardised Precipitation and Evapotranspiration Index (SPEI) for the period 1965 to 2018. Atmospheric circulation patterns during droughts were examined and the main moisture fluxes into Malawi were identified. Despite differences in the frequency, and events being asynchronous at times, droughts exhibited characteristics that were statistically similar between northern and southern Malawi. Droughts in both regions were associated with anomalous circulation that typically worked to diminish moisture advection and thus convection. Differences in the structure of the anomalies were indicative of differences in mechanisms associated with droughts in the north and south of Malawi. Three main moisture flux pathways were identified, and categorized as northeasterly, southeasterly, and northwesterly, each with a unique correlation structure with precipitation and global SSTs. Positive and negative biases of varying magnitudes were noted for drought and rainfall characteristics across the range of CMIP5 models. Such biases can be attributed to biases in moisture fluxes whose variability was found to be a key driver of summer precipitation variability across Malawi. Despite biases in moisture fluxes and their influence on precipitation biases, the majority of models exhibited moisture flux-precipitation correlations consistent with observations and reanalysis. Results from the study highlight the extent to which climate models are reliable in simulating droughts and therefore of value in developing narratives of climate variability essential for long-term development planning.</p>

scholarly journals Characteristics of Observed Atmospheric Circulation Patterns Associated with Temperature Extremes over North America

2012 ◽  
Vol 25 (20) ◽  
pp. 7266-7281 ◽  
Author(s):  
Paul C. Loikith ◽  
Anthony J. Broccoli
Keyword(s):  
North America ◽  
Atmospheric Circulation ◽  
Large Scale ◽  
Climate Models ◽  
Extreme Temperature ◽  
Future Climate Change ◽  
Temperature Extremes ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
Patterns And Processes

Abstract Motivated by a desire to understand the physical mechanisms involved in future anthropogenic changes in extreme temperature events, the key atmospheric circulation patterns associated with extreme daily temperatures over North America in the current climate are identified. The findings show that warm extremes at most locations are associated with positive 500-hPa geopotential height and sea level pressure anomalies just downstream with negative anomalies farther upstream. The orientation, physical characteristics, and spatial scale of these circulation patterns vary based on latitude, season, and proximity to important geographic features (i.e., mountains, coastlines). The anomaly patterns associated with extreme cold events tend to be similar to, but opposite in sign of, those associated with extreme warm events, especially within the westerlies, and tend to scale with temperature in the same locations. Circulation patterns aloft are more coherent across the continent than those at the surface where local surface features influence the occurrence of and patterns associated with extreme temperature days. Temperature extremes may be more sensitive to small shifts in circulation at locations where temperature is strongly influenced by mountains or large water bodies, or at the margins of important large-scale circulation patterns making such locations more susceptible to nonlinear responses to future climate change. The identification of these patterns and processes will allow for a thorough evaluation of the ability of climate models to realistically simulate extreme temperatures and their future trends.

scholarly journals Dominant Modes of Moisture Flux Anomalies over North America

2005 ◽  
Vol 6 (2) ◽  
pp. 194-209 ◽  
Author(s):  
Francina Dominguez ◽  
Praveen Kumar
Keyword(s):  
United States ◽  
North America ◽  
Atmospheric Circulation ◽  
Moisture Flux ◽  
Eof Analysis ◽  
Anomaly Field ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
Complex Eof ◽  
Precipitation Events

Abstract This study investigates the principal modes of seasonal moisture flux transport over North America, analyzing their possible dependence on large-scale atmospheric circulation patterns. It uses 23 yr (1979–2001) of 6-hourly data from the NCEP–NCAR reanalysis I project. Complex empirical orthogonal function (complex-EOF) analysis is implemented on the vertically integrated and seasonally averaged moisture flux, to identify the dominant modes. For every season, the characteristic spatial pattern of the two most dominant modes is compared to the geopotential height anomaly field and precipitation anomaly field using correlation analysis. The two dominant winter modes capture the variability in the moisture flux field associated with extreme precipitation events over the western coast of the United States. The first winter mode captures 52% of the variability of the season and is related to the strong ENSO events of 1982/83 and 1997/98 (El Niño) and 1989 (La Niña). The second winter mode captures anomalous high moisture flux over the southwest related to the east Pacific teleconnection pattern. The intense moisture transport associated with high-precipitation events in the central United States (including the 1993 flood) is captured by summer mode 1, while the second mode of the summer season captures the moisture flux variability related to the 1983 and 1988 droughts. The results show that these summer flood and drought events are characterized by very different moisture flux anomalies and are not the positive and negative phases of a given mode. The use of complex-EOF analysis captures extreme hydrologic events as characteristic modes of interannual variability and allows a better understanding of the atmospheric circulation patterns associated with these events.

scholarly journals Antarctic moisture flux and net accumulation from global atmospheric analyses

1995 ◽  
Vol 21 ◽  
pp. 149-156 ◽  
Author(s):  
W.F. Budd ◽  
P. A. Reid ◽  
L.J. Minty
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Moisture Flux ◽  
Global Climate Models ◽  
Atmospheric Moisture ◽  
Prediction Scheme ◽  
Moisture Fluxes ◽  
New Generation ◽  
The Antarctic

Previous attempts to derive the Antarctic surface net accumulation distribution from atmospheric-moisture fluxes, in reasonable agreement with the observed distribution, have encountered many difficulties. The present analysis uses the Australian Bureau of Meteorology Global Atmospheric Assimilation and Prediction Scheme (GASP), which has been operational since 1989, to derive the net air-mass and moisture fluxes over the Antarctic. It is shown that the annual mean net surface accumulation closely resembles the glaciologically observed distribution and provides a physical basis for the observed pattern, through the moisture transports. The variations with latitude and elevation and through the annual cycle are also well reproduced. Although some mass-closure errors still exist, they are expected to become insignificant with the new generation of improved analysis schemes. Consequently the atmospheric analyses can provide a sound basis for both assessing the performance of global climate models in simulating Antarctic accumulation rates and monitoring long-term changes which may occur with global warming.

scholarly journals Antarctic moisture flux and net accumulation from global atmospheric analyses

1995 ◽  
Vol 21 ◽  
pp. 149-156 ◽  
Author(s):  
W.F. Budd ◽  
P. A. Reid ◽  
L.J. Minty
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Moisture Flux ◽  
Global Climate Models ◽  
Atmospheric Moisture ◽  
Prediction Scheme ◽  
Moisture Fluxes ◽  
New Generation ◽  
The Antarctic

Previous attempts to derive the Antarctic surface net accumulation distribution from atmospheric-moisture fluxes, in reasonable agreement with the observed distribution, have encountered many difficulties. The present analysis uses the Australian Bureau of Meteorology Global Atmospheric Assimilation and Prediction Scheme (GASP), which has been operational since 1989, to derive the net air-mass and moisture fluxes over the Antarctic. It is shown that the annual mean net surface accumulation closely resembles the glaciologically observed distribution and provides a physical basis for the observed pattern, through the moisture transports. The variations with latitude and elevation and through the annual cycle are also well reproduced. Although some mass-closure errors still exist, they are expected to become insignificant with the new generation of improved analysis schemes. Consequently the atmospheric analyses can provide a sound basis for both assessing the performance of global climate models in simulating Antarctic accumulation rates and monitoring long-term changes which may occur with global warming.

scholarly journals Daily Atmospheric Circulation Patterns and Their Influence on Dry/Wet Events in Iran

Atmosphere ◽  
2022 ◽  
Vol 13 (1) ◽  
pp. 81
Author(s):  
Zahra Ghassabi ◽  
Ebrahim Fattahi ◽  
Maral Habibi
Keyword(s):  
Atmospheric Circulation ◽  
Red Sea ◽  
Principal Component ◽  
Moisture Flux ◽  
The South ◽  
Flux Divergence ◽  
Atmospheric Circulation Patterns ◽  
Pressure Surface ◽  
Pi Index ◽  
Circulation Patterns

Analyzing atmospheric circulation patterns characterize prevailing weather in a region. The method of principal component analysis and clustering was used to classify daily atmospheric circulation patterns. The average daily geopotential height of 500 hPa with 0.5° resolution of the ECMWF (1990–2019) were extracted from the Middle East. The S array was used to identify air types, and k-means clustering was used to classify daily air types. All days were divided into eighteen groups. Then, the surface maps and moisture flux divergence at the 850-hPa level of each pattern were studied. The, the connection between circulation patterns and precipitation occurrence is investigated by the PI index. The existence of a variety of precipitation and temperature regimes and consequent dry/wet periods is related to the type and frequency of the circulation patterns. In patterns with south to southwesterly currents, the low-pressure surface center extends from the south of the Red Sea to southern Turkey and is associated with the mid-level trough, where the moisture fluxes converge in the south of the Red Sea, southwest/south of Iran, and east of the Mediterranean Sea. Therefore, according to the intensity of the patterns, the most precipitation falls in the country’s western half, and the Zagros Mountain’s wind side. With the eastward movement of the Cyclonic patterns, the rainfall area extends to the eastern half of the country. With the pattern that the thermal low surface pressure extends to 35 °N latitude and is associated with the mid-level subtropical high, almost no rain occurs in the country.

scholarly journals Comparison between Observed and Model-Simulated Atmospheric Circulation Patterns Associated with Extreme Temperature Days over North America Using CMIP5 Historical Simulations

2015 ◽  
Vol 28 (5) ◽  
pp. 2063-2079 ◽  
Author(s):  
Paul C. Loikith ◽  
Anthony J. Broccoli
Keyword(s):  
North America ◽  
Atmospheric Circulation ◽  
General Circulation ◽  
Climate Models ◽  
Extreme Temperature ◽  
Coupled Model ◽  
General Circulation Models ◽  
Multimodel Ensemble ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns

Abstract Circulation patterns associated with extreme temperature days over North America, as simulated by a suite of climate models, are compared with those obtained from observations. The authors analyze 17 coupled atmosphere–ocean general circulation models contributing to the fifth phase of the Coupled Model Intercomparison Project. Circulation patterns are defined as composites of anomalies in sea level pressure and 500-hPa geopotential height concurrent with days in the tails of temperature distribution. Several metrics used to systematically describe circulation patterns associated with extreme temperature days are applied to both the observed and model-simulated data. Additionally, self-organizing maps are employed as a means of comparing observed and model-simulated circulation patterns across the North American domain. In general, the multimodel ensemble resembles the observed patterns well, especially in areas removed from complex geographic features (e.g., mountains and coastlines). Individual model results vary; however, the majority of models capture the major features observed. The multimodel ensemble captures several key features, including regional variations in the strength and orientation of atmospheric circulation patterns associated with extreme temperatures, both near the surface and aloft, as well as variations with latitude and season. The results from this work suggest that these models can be used to comprehensively examine the role that changes in atmospheric circulation will play in projected changes in temperature extremes because of future anthropogenic climate warming.

Sign in / Sign up

Export Citation Format

Share Document