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Multi-Decadal Variability in the Southeastern United States

Multi-Decadal Variability in the Southeastern United States. Marcus D. Williams March 15, 2010. Multidecadal Variability in the Southeast. Alabama Annual Temperature. Warm period 1920-1957. Cold period 1958-1998. Same multi-decadal pattern is displayed in the raw, unadjusted station data

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Multi-Decadal Variability in the Southeastern United States

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  1. Multi-Decadal Variability in the Southeastern United States Marcus D. Williams March 15, 2010

  2. Multidecadal Variability in the Southeast Alabama Annual Temperature Warm period 1920-1957 Cold period 1958-1998

  3. Same multi-decadal pattern is displayed in the raw, unadjusted station data • 1920-1957: Warm regime (WR) • 1958-1998: Cold regime (CR) Cold period 1958-1998 Warm period 1920-1957

  4. Objectives • Characterize the nature of multi-decadal temperature variability in the Southeastern United States • Seasonality • Spatial Coherence • Extremes • Magnitude in comparison to other variability • Is the signal of the variability more prevalent in any particular season • Is the variability affecting the occurrence of temperature extremes

  5. Seasonality • To examine the regime shift, Probability Distribution Function (PDF) plots where created for all seasons at each station • The PDF plots allow examination of the regime shift at all ranges of temperatures as well as the mean for the chosen season. • Winter and Summer max and min temperatures show the strongest signal. Signal present in Spring and Fall, although not as strong and consistent as Winter and Summer. • Signal weak in Florida Summer max and min temperatures • Signal also dampened by proximity of station to water and in the mountain regions

  6. Chapel Hill, NC

  7. Camp Hill, AL

  8. Difference in Mean • Difference in the mean temperatures between the CR and WR

  9. Difference in Mean

  10. Shift in occurrences of extremes • With the shift displayed in the temperature PDF’s, one would expect an increased occurrence of temperatures at the tails of the distribution • Thresholds were set at 32°F and 95°F and counts of occurrences per year where made. • As expected there was a difference in the in the occurrence of 32°F and 95°F between the warm and cold regime. • Talladega (AL), Lake City (FL), and Chapel Hill (NC) will be used as examples to illustrate this point

  11. Talladega, AL • Substantial shift in the number of days temperature reached 95°F or higher

  12. Lake City, FL

  13. Chapel Hill, NC

  14. Summary • Clear shift in temperature regime between the periods 1920-1957 (WR) and 1958-1998 (CR) • Signal strongest during winter season and slightly damped by proximity to mountains and bodies of water • Why? • Continental Air masses from upstream contributing to variability (Anthony Arguiez) • Signal damped during the summer season in Florida because of tropical climate dominated by the Bermuda High ( guesswork) • Number of days at or above 95°F increased for the WR • Number of days at or below 32°F increased for the CR • Questions to be answered • Test the independence of data to verify statistical significance of regime shift • What are the causes for this multi-decadal shift in temperatures and is the signal present in future regions of the Southeastern U.S.

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