| Long-term temperature and precipitation records in the Midwest are examined in order to determine if interdecadal variability associated with the Pacific Decadal Oscillation (PDO) acts to modulate the El Nino Southern Oscillation (ENSO) related interannual variability of Midwestern climates. Power spectrum analysis demonstrates that significant El Nino Southern Oscillation (ENSO) related variability between 3 and 7 years as well as significant interdecadal variability between 12--15 years and at approximately 21 year time periods exist within these time series. This interdecadal variability is suggested to represent the time periods in which the PDO acts to modulate the ENSO-related variability of Midwestern climates. In addition, it was determined in this study that the ENSO-related variability of Midwestern climates was very high during the PDO 1 periods (e.g., 1925--1946 and 1977--1999) and was much lower during the PDO 2 (e.g., 1900--1924, 1947--1976, and 2000 to present) periods. These results suggest that the ENSO-related impacts on Midwestern climates change on interdecadal time scales, further suggesting that the seasonal climates experienced during an ENSO event may not necessarily mimic those of another similar ENSO event in the future. So, from a forecasting point, in order to obtain more skillful seasonal long-term forecasts, the interdecadal variability should be considered as being superimposed upon the interannual variations. |
