Search Results
You are looking at 1 - 5 of 5 items for
- Author or Editor: Jill S. M. Coleman x
- Refine by Access: All Content x
Abstract
Blizzards are extreme winter storms that are defined by strong winds and falling or blowing snow that significantly reduces visibility for an extended period of time. For the conterminous United States, blizzard occurrence by county was compiled from Storm Data for 55 winter seasons from 1959/60 to 2013/14. Spatiotemporal patterns were examined for blizzard seasons (September–August) at annual, decadal, and monthly frequencies. Linear regression and spectral analysis were used to detect any blizzard cycles or trends. Societal impacts such as fatalities, injuries, property damage, and federal disaster declarations were also tallied. Data revealed 713 blizzards over the 55 years, with a mean of 13 events per season. Seasonal blizzard frequency ranged from one blizzard in 1980/81 to 32 blizzards in 2007/08. The average area per blizzard was 83 474 km2, or approximately the size of South Carolina. Blizzard probabilities ranged from 1.8% to 76.4%, with a distinct blizzard zone in North Dakota, western Minnesota, and northern South Dakota. Every month except July, August, and September has reported blizzards with a peak occurrence in December and January. Federal disaster declarations resulting from blizzards totaled 57, with more than one-half of them occurring in the twenty-first century. Storm Data attributed 711 fatalities during the 55-yr study period, with an average of one individual per event; 2044 injuries were reported, with a mean of nearly three per blizzard. Property damage totaled approximately $9.11 billion in unadjusted dollars, with an approximate mean of $12.6 million per storm.
Abstract
Blizzards are extreme winter storms that are defined by strong winds and falling or blowing snow that significantly reduces visibility for an extended period of time. For the conterminous United States, blizzard occurrence by county was compiled from Storm Data for 55 winter seasons from 1959/60 to 2013/14. Spatiotemporal patterns were examined for blizzard seasons (September–August) at annual, decadal, and monthly frequencies. Linear regression and spectral analysis were used to detect any blizzard cycles or trends. Societal impacts such as fatalities, injuries, property damage, and federal disaster declarations were also tallied. Data revealed 713 blizzards over the 55 years, with a mean of 13 events per season. Seasonal blizzard frequency ranged from one blizzard in 1980/81 to 32 blizzards in 2007/08. The average area per blizzard was 83 474 km2, or approximately the size of South Carolina. Blizzard probabilities ranged from 1.8% to 76.4%, with a distinct blizzard zone in North Dakota, western Minnesota, and northern South Dakota. Every month except July, August, and September has reported blizzards with a peak occurrence in December and January. Federal disaster declarations resulting from blizzards totaled 57, with more than one-half of them occurring in the twenty-first century. Storm Data attributed 711 fatalities during the 55-yr study period, with an average of one individual per event; 2044 injuries were reported, with a mean of nearly three per blizzard. Property damage totaled approximately $9.11 billion in unadjusted dollars, with an approximate mean of $12.6 million per storm.
Abstract
The relationship between the Pacific–North American (PNA) teleconnection pattern and Ohio River Valley (ORV) winter precipitation and hydrology is described. The PNA is significantly linked to moisture variability in an area extending from southeastern Missouri, northeastward over states adjacent to the Ohio River through Ohio. Maximum correlation between the PNA index and station precipitation peaks in southern Indiana at r = −0.71, making the circulation/climate teleconnection one of the strongest in the Northern Hemisphere. The North Pacific index (NPI), a Pacific basin sea level pressure index that is highly correlated to the PNA, confirms a strong circulation–ORV precipitation relationship extending back to 1899. In contrast, measures such as the Tahiti–Darwin Southern Oscillation index (SOI) and Niño-3.4 (5°S–5°N, 120°–170°W) sea temperatures are not significantly correlated to ORV winter precipitation. Wettest (driest) winters occur with zonal (meridional) flow with the PNA negative (positive) and North Pacific sea level pressure anomalously high (low). Moisture flux convergence extends much farther north from the Gulf of Mexico in the wet winters, compared to dry, and excess of precipitation over evaporation (moisture budget) is over 100 mm larger throughout much of the ORV. Wet winters, particularly those of 1949 and 1950 changed the ORV hydrology to one of extensive wet conditions, as measured by the Palmer hydrologic drought index (PHDI). Unusually dry winters, however, appear to have less impact on the index; many ORV climate divisions remain moist through the winter despite low precipitation. Winter mean streamflow along the Ohio River and its tributaries varies significantly between PNA extremes, with river discharges up to 100% higher in PNA-negative winters as opposed to PNA-positive winters.
Abstract
The relationship between the Pacific–North American (PNA) teleconnection pattern and Ohio River Valley (ORV) winter precipitation and hydrology is described. The PNA is significantly linked to moisture variability in an area extending from southeastern Missouri, northeastward over states adjacent to the Ohio River through Ohio. Maximum correlation between the PNA index and station precipitation peaks in southern Indiana at r = −0.71, making the circulation/climate teleconnection one of the strongest in the Northern Hemisphere. The North Pacific index (NPI), a Pacific basin sea level pressure index that is highly correlated to the PNA, confirms a strong circulation–ORV precipitation relationship extending back to 1899. In contrast, measures such as the Tahiti–Darwin Southern Oscillation index (SOI) and Niño-3.4 (5°S–5°N, 120°–170°W) sea temperatures are not significantly correlated to ORV winter precipitation. Wettest (driest) winters occur with zonal (meridional) flow with the PNA negative (positive) and North Pacific sea level pressure anomalously high (low). Moisture flux convergence extends much farther north from the Gulf of Mexico in the wet winters, compared to dry, and excess of precipitation over evaporation (moisture budget) is over 100 mm larger throughout much of the ORV. Wet winters, particularly those of 1949 and 1950 changed the ORV hydrology to one of extensive wet conditions, as measured by the Palmer hydrologic drought index (PHDI). Unusually dry winters, however, appear to have less impact on the index; many ORV climate divisions remain moist through the winter despite low precipitation. Winter mean streamflow along the Ohio River and its tributaries varies significantly between PNA extremes, with river discharges up to 100% higher in PNA-negative winters as opposed to PNA-positive winters.
Abstract
A synoptic climatological weather classification scheme incorporating both surface and upper-air data is developed for the central United States based on an automated two-step cluster analysis. It employs daily NCEP–NCAR reanalysis data over all seasons of 57 yr (1948–2004) in creating synoptic types from surface and upper-air (925, 850, 700, and 500 hPa) temperature and humidity data as well as sea level pressure, geopotential heights, and winds aloft. The cluster analysis creates 10 synoptic types exhibiting distinct seasonal preferences, with three each that occur primarily in summer and winter, and four that occur primarily in winter and the transition seasons, particularly spring. The typing scheme generates synoptic patterns largely characterized by distinctive surface circulations, baroclinic vertical structure, and thermal advection. Interannual variations occur in the frequencies of the synoptic types, some of which are out of phase with each other. The annual frequencies of two winter synoptic types, associated respectively with strong zonal and meridional flow, are highly correlated (r ≫ 0.63–0.73) to the phase of the Pacific–North American teleconnection pattern, while Niño-3.4 equatorial Pacific sea surface temperatures are linked to a synoptic type producing low pressure around the Gulf Coast.
Abstract
A synoptic climatological weather classification scheme incorporating both surface and upper-air data is developed for the central United States based on an automated two-step cluster analysis. It employs daily NCEP–NCAR reanalysis data over all seasons of 57 yr (1948–2004) in creating synoptic types from surface and upper-air (925, 850, 700, and 500 hPa) temperature and humidity data as well as sea level pressure, geopotential heights, and winds aloft. The cluster analysis creates 10 synoptic types exhibiting distinct seasonal preferences, with three each that occur primarily in summer and winter, and four that occur primarily in winter and the transition seasons, particularly spring. The typing scheme generates synoptic patterns largely characterized by distinctive surface circulations, baroclinic vertical structure, and thermal advection. Interannual variations occur in the frequencies of the synoptic types, some of which are out of phase with each other. The annual frequencies of two winter synoptic types, associated respectively with strong zonal and meridional flow, are highly correlated (r ≫ 0.63–0.73) to the phase of the Pacific–North American teleconnection pattern, while Niño-3.4 equatorial Pacific sea surface temperatures are linked to a synoptic type producing low pressure around the Gulf Coast.
Abstract
A 124 (1882–2005) summer record of total surface energy content consisting of time series of surface equivalent temperature (TE ) and its components T (mean air temperature) and Lq/cp (moist enthalpy, denoted Lq) is developed, quality controlled, and analyzed for Columbus, Ohio, where long records of monthly dewpoint temperature are available. The analysis shows that the highest TE occurs during the summer of 1995 when both T and Lq were very high, associated with a severe midwestern heat wave. That year contrasts with the hot summers of 1930–36, when Lq and TE had relatively low or negative anomalies (low humidity) compared to those of T. Following the 1930–36 summers, T and Lq departures are much more typically the same sign in individual summers, and the two parameters develop a statistically significant high positive correlation into the twenty-first century. Mean T and Lq departures from the long-term normal have opposite signs, however, when summers are stratified either by seasonal total rainfall amounts or by the Palmer drought severity soil moisture index. Normalized trends of T, Lq, and TE are downward from 1940 to 1964 with those of TE exceeding T. Since 1965, however, significant positive T trends slightly exceed TE in magnitude and those of dewpoint temperature and Lq are comparatively lower. A highly significant upward trend in minimum temperatures especially dominates the T variability, creating a significant downward trend in the temperature range that dominates recent summer climate variability more than moisture trends. Regional moisture flux variations are largest away from Columbus, over the upper Midwest and western Atlantic Ocean, during its seasonal extremes in total surface energy.
Abstract
A 124 (1882–2005) summer record of total surface energy content consisting of time series of surface equivalent temperature (TE ) and its components T (mean air temperature) and Lq/cp (moist enthalpy, denoted Lq) is developed, quality controlled, and analyzed for Columbus, Ohio, where long records of monthly dewpoint temperature are available. The analysis shows that the highest TE occurs during the summer of 1995 when both T and Lq were very high, associated with a severe midwestern heat wave. That year contrasts with the hot summers of 1930–36, when Lq and TE had relatively low or negative anomalies (low humidity) compared to those of T. Following the 1930–36 summers, T and Lq departures are much more typically the same sign in individual summers, and the two parameters develop a statistically significant high positive correlation into the twenty-first century. Mean T and Lq departures from the long-term normal have opposite signs, however, when summers are stratified either by seasonal total rainfall amounts or by the Palmer drought severity soil moisture index. Normalized trends of T, Lq, and TE are downward from 1940 to 1964 with those of TE exceeding T. Since 1965, however, significant positive T trends slightly exceed TE in magnitude and those of dewpoint temperature and Lq are comparatively lower. A highly significant upward trend in minimum temperatures especially dominates the T variability, creating a significant downward trend in the temperature range that dominates recent summer climate variability more than moisture trends. Regional moisture flux variations are largest away from Columbus, over the upper Midwest and western Atlantic Ocean, during its seasonal extremes in total surface energy.
