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In South Africa cold spells are defined as 3 or more consecutive days with minimum temperatures below 2.5 degree Celsius, severe cold spells are 3 or more consecutive days with minima below freezing point, i.e. 0 degree Celsius, while extreme cold spells are defined as 3 or more consecutive days with temperatures below -2.5 degree Celsius. In South Africa the main causes of cold spells are outbreaks of Antarctic air which follow cold fronts, and in the southern hemisphere with its vast tracts of oceans, these cold fronts are frequently well developed. Cold spells affect many sectors, including health, especially exposure to low temperatures, energy, with marked increases in electricity consumption for heating purposes. In agriculture some consequences of cold spells include frost and freeze impacts, especially if the cold spells occur early or livestock losses, where the livestock has not been protected from the cold. The temperature database created for South Africa by Schulze and Maharaj (2004) was used to compute frequencies of cold spells. In this temperature database daily maximum and minimum temperatures were generated for the 50 year period 1950 - 1999 at 429 - 700 one arc minute grid points covering the area, by using observed daily temperatures of varying durations from 973 temperature stations with quality controlled data which were infilled and extended to the common 50 year period by techniques outlined in Schulze and Maharaj (2004) and interpolated/extrapolated using regional and monthly temperature lapse rates. What was not accounted for in mapping cold spell occurrences at each of the grid points was whether a point was located in a valley, and therefore subject to cross-sectional nocturnal cold air drainage from crest to valley bottom in the winter months, or on a crest. Schulze and Maharaj (2004) found some differences between minimum temperatures from stations located in valleys vs those on crests, but were not able to map such temperature differences because of the complex dynamics of determining longitudinal cold air drainage within a valley, i.e. from higher altitudes of the upper valley to the lower altitudes of the lower valley |
| summary:
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In South Africa cold spells are defined as 3 or more consecutive days with minimum temperatures below 2.5 degree Celsius, severe cold spells are 3 or more consecutive days with minima below freezing point, i.e. 0 degree Celsius, while extreme cold spells are defined as 3 or more consecutive days with temperatures below -2.5 degree Celsius. In South Africa the main causes of cold spells are outbreaks of Antarctic air which follow cold fronts, and in the southern hemisphere with its vast tracts of oceans, these cold fronts are frequently well developed. Cold spells affect many sectors, including health, especially exposure to low temperatures, energy, with marked increases in electricity consumption for heating purposes. In agriculture some consequences of cold spells include frost and freeze impacts, especially if the cold spells occur early or livestock losses, where the livestock has not been protected from the cold. The temperature database created for South Africa by Schulze and Maharaj (2004) was used to compute frequencies of cold spells. In this temperature database daily maximum and minimum temperatures were generated for the 50 year period 1950 - 1999 at 429 - 700 one arc minute grid points covering the area, by using observed daily temperatures of varying durations from 973 temperature stations with quality controlled data which were infilled and extended to the common 50 year period by techniques outlined in Schulze and Maharaj (2004) and interpolated/extrapolated using regional and monthly temperature lapse rates. What was not accounted for in mapping cold spell occurrences at each of the grid points was whether a point was located in a valley, and therefore subject to cross-sectional nocturnal cold air drainage from crest to valley bottom in the winter months, or on a crest. Schulze and Maharaj (2004) found some differences between minimum temperatures from stations located in valleys vs those on crests, but were not able to map such temperature differences because of the complex dynamics of determining longitudinal cold air drainage within a valley, i.e. from higher altitudes of the upper valley to the lower altitudes of the lower valley |
| extent:
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[[16,-34],[32,-22]] |
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thumbnail/thumbnail.png |
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1 |
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["Data","Service","Map Service","ArcGIS Server"] |
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| catalogPath:
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| title:
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Map |
| type:
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Map Service |
| url:
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| tags:
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["cold spells","severe weather","Weather and climate","minimum temperature"] |
| culture:
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en-US |
| name:
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coldspells2 |
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5A2AE501-5478-4B02-B027-37668CE8478B |
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0 |
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WGS_1984_Web_Mercator_Auxiliary_Sphere |