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In this study, a North American Regional Reanalysis (NARR)‐based climate dataset of wind and Pasquill stability class is developed for the North American Great Lakes region. Motivated by the need to update the limited wind and Pasquill stability class climatology previously incorporated into a livestock odour nuisance‐mitigation application used in Michigan, this study is motivated more generally by the lack of a long‐term climate dataset suitable for studies of atmospheric dispersion in the Great Lakes region. As a preliminary step, NARR 10‐m wind speed, 10‐m wind direction, and 2‐m temperature are evaluated at eight weather stations in Michigan and northern Indiana, and the wind speed variable is subsequently bias‐corrected. To derive a Pasquill stability class dataset from the NARR variables, an existing empirical relationship between Pasquill stability class and Richardson number is applied to a previously developed NARR‐derived Richardson number dataset covering the period 1979–2008. Pasquill stability class frequency in NARR is subsequently evaluated using observations at two flux towers in Illinois. Although a tendency is noted for the NARR‐derived Pasquill stability class dataset to underestimate the frequency of stable and unstable conditions, and overestimate the frequency of neutral conditions, the analysis shows that the 10‐m wind speed bias‐correction procedure yields a frequency distribution that is in better agreement with the observations than the non‐bias‐corrected dataset. Finally, an analysis of the spatial and temporal variability of livestock odour dispersion potential in Michigan is provided as an example application of the NARR‐based wind and Pasquill stability class climate dataset. [ABSTRACT FROM AUTHOR]

Wildfire regimes respond to atmospheric variability on multiple time scales from interannual variations of drought to daily fluctuations of humidity and wind. Synoptic weather patterns effectively link both short- and long-term atmospheric variability, and thus, understanding fire-prone synoptic patterns is an integral part of fire management programs. Different analysis procedures of varying complexity have been used to identify the most common synoptic weather patterns conducive to wildfires. In this study, we examine the utility of three synoptic-pattern classification methodologies, namely Composite, Empirical Orthogonal Function (EOF), and Self Organizing Map (SOM). We focused on the synoptic weather patterns associated with 203 wildfires that burned 50,000 acres (20,250 ha) or more and 80 wildfires that burned 100,000 acres (40,500 ha) or more in the Northwestern United States between 1984 and 2014. The basic 500-hPa geopotential height patterns identified by the three analysis methods were found to be similar for the two fire-size categories, but the strengths of the geopotential height anomalies were larger for the larger size fires. All three methods were able to consistently identify the dominant pattern with only small differences in strength and position of the anomalies, but the EOF and SOM methods yielded other less dominant, but still important, patterns. Particularly, the SOM method captured transitional synoptic patterns that may account for 20–30% of these large wildfires. [ABSTRACT FROM AUTHOR]

ABSTRACT The mean climatology, seasonal and interannual variability and trend of wind speeds at the hub height (80 m) of modern wind turbines over China and its surrounding regions are revisited using 33-year (1979-2011) wind data from the Climate Forecast System Reanalysis ( CFSR) that has many improvements including higher spatial resolution over previous global reanalysis products. Mean 80-m wind speeds are consistently higher over China Seas and the ocean areas than over land, and inside China high winds are found in areas of Inner Mongolia and the Tibetan Plateau. There is a considerable seasonal variability that reflects primarily the influence of East and Southeast Asia Monsoon with generally higher speeds in winter followed by summer, and weaker winds in autumn, followed by spring. There is also a strong interannual variability, and regions of larger amplitude of variability coincide with regions of higher mean winds. A decreasing trend, dominated by a sharp decline beginning in 2005, is seen across China and the surrounding seas in summer and autumn, and the summer trends over land and over ocean appear to be related respectively to the Pacific Decadal Oscillation ( PDO) and the East Asian summer monsoon. Trends are not consistent across the region in spring and winter, however, with positive trends over some areas in northeastern and northwestern China, Mongolia and tropical oceans whereas negative trends in other regions. Nearly all areas of China experience mean annual 80-m wind speed less than 6.9 m s−1 (wind power classes of 1-2) except for some areas of Inner Mongolia where mean annual 80-m wind speeds exceed 6.9 m s−1 (Classes 3 or higher, suitable for wind energy development). China Seas and ocean areas generally fall in Class 3 or above, with the Taiwan and Luzon Straights reaching the highest Class 7. [ABSTRACT FROM AUTHOR]

Recent research suggests that high levels of ambient near-surface atmospheric turbulence are often associated with rapid and sometimes erratic wildland fire spread that may eventually lead to large burn areas. Previous research has also examined the feasibility of using near-surface atmospheric turbulent kinetic energy (TKE s) alone or in combination with the Haines index (HI) as an additional indicator of anomalous atmospheric conditions conducive to erratic or extreme fire behavior. However, the application of TKE s-based indices for operational fire-weather predictions in the United States on a regional or national basis first requires a climatic assessment of the spatial and temporal patterns of the indices that can then be used for testing their operational effectiveness. This study provides an initial examination of some of the spatial and temporal variability patterns across the United States of TKE s and the product of HI and TKE s (HITKE s) using data from the North American Regional Reanalysis dataset covering the 1979-2008 period. The analyses suggest that there are regional differences in the behavior of these indices and that regionally dependent threshold values for TKE s and HITKE s may be needed for their potential use as operational indicators of anomalous atmospheric turbulence conditions conducive to erratic fire behavior. The analyses also indicate that broad areas within the northeastern, southeastern, and southwestern regions of the United States have experienced statistically significant positive trends in TKE s and HITKE s values over the 1979-2008 period, with the most substantial increases in values occurring over the 1994-2008 period. [ABSTRACT FROM AUTHOR]

The hydroclimate of the western United States is influenced by strong interannual variability of atmospheric circulation, much of which is associated with the El Niño-Southern Oscillation (ENSO). Precipitation anomalies during ENSO often show opposite and spatially coherent dry and wet patterns in the Northwest and California or vice versa. The role of orography in establishing mesoscale ENSO anomalies in the western United States is examined based on observed precipitation and temperature data at 1/88 spatial resolution and a regional climate simulation at 40-km spatial resolution. Results show that during El Niño or La Niña winters, strong precipitation anomalies are found in northern California, along the southern California coast, and in the northwest mountains such as the Olympic Mountains, the Cascades, and the northern Rockies. These spatial features, which are strongly affected by topography, are surprisingly well reproduced by the regional climate simulation. A spatial feature investigated further is the positive-negative-positive precipitation anomaly found during El Niño years in the Olympic Mountains, and on the west side and east side of the Cascades in both observations and regional simulation. Observed streamflows of river basins located in those areas are found to be consistent with the precipitation anomalies. The spatial distribution of the precipitation anomalies is investigated by relating flow direction and moisture to the orientation of mountains and orographic precipitation. On the west side of the north-south-oriented Cascade Range, the increase in atmospheric moisture is not enough to compensate for the loss of orographic precipitation associated with a change in flow direction toward the southwest during El Niño years. In California, both the increase in atmospheric moisture and shift in wind direction toward the southwest enhance precipitation along the Sierra, which is oriented northwest to... [ABSTRACT FROM AUTHOR]

This paper investigates the diurnal evolution of thermally driven plain-mountain winds, up- and down-valley winds, up- and downslope winds, and land-lake breezes for summer fair weather conditions in four regions of the Intermountain West where dense wind networks have been operated. Because of the diverse topography in these regions, the results are expected to be broadly representative of thermally driven wind climates in the Intermountain West. The regions include the Wasatch Front Valleys of northern Utah, the Snake River Plain of Idaho, the southern Nevada basin and range province, and central Arizona. The analysis examines wind characteristics, including the regularity of the winds and interactionsof the four types of thermally driven winds, using meteorological data from the University of Utah's MesoWest network. In general, on fair weather days, winds in all four regions exhibit a consistent direction from day to day at a given hour. A measure of this wind consistency is defined. The nighttime hours exhibit a generally higher consistency than thedaytime hours. Lower consistency during the day-night and night-day transition periods reflects day-to-day variations in the timing of wind system reversals. Thermally driven circulations are similar in the four regions, but the WasatchFront Valleys are influenced by lake breezes from the adjacent Great Salt Lake, the Snake River Plain is influenced by along-plain circulations and localized outflow from the Central Idaho Mountains, and winds in both southern Nevada and central Arizona are influenced by plain-mountain circulations associated with regionalscale contrasts in elevation andsurface heating. [ABSTRACT FROM AUTHOR]