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Twentieth century trends in dew point temperature throughout the Upper Midwest

Twentieth century trends in dew point temperature throughout the Upper Midwest. Jesse Wartman. Mentors: Daryl Herzmann and Dr. Eugene Takle. Why are dew-point temperatures important?. Important in forecasting Used for specific and relative humidities

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Twentieth century trends in dew point temperature throughout the Upper Midwest

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  1. Twentieth century trends in dew point temperature throughout the Upper Midwest Jesse Wartman Mentors: Daryl Herzmann and Dr. Eugene Takle

  2. Why are dew-point temperatures important? • Important in forecasting • Used for specific and relative humidities • Regulate transpiration and evaporation processes • Key factors in the surface energy and hydrological budgets • Water vapor is the strongest contribution to the greenhouse effect

  3. Past Studies • Gaffen and Ross (1999) • Increase through spring and fall • Robinson (1998) • Dew points were lower in the Upper Midwest during the winter • Robinson (2000) • Increase of 0.9°F per 100 years over U.S. • Increase over spring and fall

  4. Possible Errors • Non-uniform stations • Technology and instrument changes • 1950s - sling psychrometers • 1960s – dial hygrothermometers • Most recent – HO-83 dial hygrothermometer (NWS)

  5. Hypotheses • Dew-point temperatures have experienced significant, positive trends over the past 44 years in the Upper Midwest. • Those dew-point temperature tendencies are no different from trends that have been found across the rest of the United States in past studies.

  6. Data and Methods • Hourly obs through IEM from the NCDC • 1961-2005 • Monthly • Seasonal • Winter - December, January, & February • Spring - March, April & May • Summer - June, July & August • Fall - September, October, & November • Yearly • Decadal

  7. Observation Stations Legend of Cities • St. Louis • Kansas City • Omaha • Des Moines • Sioux Falls • Minneapolis

  8. Missing Data • Sioux Falls – 0% • Minneapolis – 18% - data gap – decadal averages were substituted in, no significant change so left out • Omaha – 30.11% - no data before 1974 • Des Moines – 1.33% - data gap • Kansas City – 27.27% - no data before 1973 • St. Louis – 27.27% - no data before 1973

  9. Significance • Significant if P-value < 0.05 • Semi-significant if P-value < 0.1 • P-Value – calculated in JMP, observed significance probability from t-ratios • T-ratio – tests hypothesis that each parameter is zero, ratio of the parameter estimate to its standard error

  10. RESULTS Monthly Climatic Trends Seasonal climatic trends Yearly average climatic trends Decadal climatic trends Twenty-two year climatic trends Extreme days Precipitable water

  11. Monthly Climatic TrendsP-Value < 0.05–P-value < 0.1

  12. Seasonal Climatic Trends Td (°F)

  13. Seasonal Climatic Trends Td (°F)

  14. Seasonal Climatic Trends Td (°F)

  15. Seasonal Climatic Trends Td (°F)

  16. Yearly Average Climatic Trends Td (°F)

  17. Yearly Climatic Trends • Averages • Kansas City: .128* • Sioux Falls: .1* • Minneapolis: .083* • Des Moines: .077* • Omaha: .064 • St. Louis: .0084 • Total ~ 7.54°F per 100 years • 0.9°F per 100 years (Robinson, 2000)

  18. Decadal Climatic Trends Td (°F) Td (°F)

  19. Decadal Climatic Trends Td (°F) Td (°F)

  20. 1961-1983 Omaha: -64°F* St. Louis: -13°F Des Moines: -5 °F Minneapolis: -4°F Kansas City: -3°F Sioux Falls: 4°F 1984-2005 Omaha: 12°F * St. Louis: 13°F * Des Moines: 11°F * Minneapolis: 13°F * Kansas City: 14°F Sioux Falls: 11°F Twenty-two year trends

  21. Twenty-two year trends

  22. 4 2 0 -2 -4 Monthly temperature anomaly (°C) Years Monthly values for the PDO index (Jan. 1955-Oct. 2006) (Mantua, 2000) Pacific Decadal Oscillation (PDO)

  23. Extreme days: dew points over 70°F

  24. Extreme days: dew points over 75°F

  25. Precipitable Water • Surface Vapor Pressure: • Po= 1mb*e {1.81+(17.27*D)/(D+237.3)} • Precipitable Water: • h = Po/(ρw*g)

  26. Precipitable Water

  27. Implications

  28. Implications • Precipitation • Heat stress • Crop production • Soil errosion • Water supplies • Human health • Heat waves

  29. Concluding Remarks • Shift from negative trend to positive trend • Positive overall trend • Hypotheses • Dew-point temperatures have experienced significant, positive trends over the past 44 years in the Upper Midwest. -> TRUE • Those dew-point temperature tendencies are no different from trends that have been found across the rest of the United States in past studies. -> FALSE • 7.54°F over 100 years in Upper Midwest • 0.9°F over 100 years in United States

  30. Future Work • Modelling studies • Future increases? • Increase in greenhouse gases • PDO • El Niño • Atlantic Oscillation • Other factors

  31. Acknowledgements • Daryl E. Herzmann • Eugene S. Takle • Jon Hobbs

  32. Questions? • jwartman@iastate.edu • http://www.meteor.iastate.edu/~jwartman/portfolio/project.html

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