Subseasonal climate variability for North Carolina, United States

Subseasonal trends in climate variability for maximum temperature (T-max), minimum temperature (T-min) and precipitation were evaluated for 249 ground-based stations in North Carolina for 1950-2009. The magnitude and significance of the trends at all stations were determined using the non-parametric Theil-Sen Approach (TSA) and the Mann-Kendall (MK) test, respectively. The Sequential Mann-Kendall (SQMK) test was also applied to find the initiation of abrupt trend changes. The lag-1 serial correlation and double mass curve were employed to address the data independency and homogeneity. Using the MK trend test, statistically significant (confidence level >= 95% in two-tailed test) decreasing (increasing) trends by 44% (45%) of stations were found in May (June). In general, trends were decreased in T-max and increased in T-min data series in subseasonal scale. Using the TSA method, the magnitude of lowest (highest) decreasing (increasing) trend in T-max is -0.050 degrees C/year (+0.052 degrees C/year) in the monthly series for May (March) and for T-min is -0.055 degrees C/year (+0.075 degrees C/year) in February (December). For the precipitation time series using the TSA method, it was found that the highest (lowest) magnitude of 1.00 mm/year (-1.20 mm/year) is in September (February). The overall trends in precipitation data series were not significant at the 95% confidence level except that 17% of stations were found to have significant (confidence level >= 95% in two-tailed test) decreasing trends in February. The statistically significant trend test results were used to develop a spatial distribution of trends: May for T-max, June for T-min, and February for precipitation. A correlative analysis of significant temperature and precipitation trend results was examined with respect to large scale circulation modes (North Atlantic Oscillation (NAO) and Southern Oscillation Index (SOI)). A negative NAO index (positive-EI Nino Southern Oscillation (ENSO) index) was found to be associated with the decreasing precipitation in February during 1960-1980 (2000-2009). The incremental trend in T-min in the inter-seasonal (April-October) time scale can be associated with the positive NAO index during 1970-2000. (C) 2014 Elsevier B.V. All rights reserved.