A Long-Term Climatology of Southerly and Northerly Low-Level Jets for the Central United States

Climate change is having a significant effect on many allergenic plants resulting in increased pollen production and shifts in plant phenology. Although these effects have been well-studied in some areas of the world, few studies have focused on long-term changes in allergenic pollen in the South Central United States. This study examined airborne pollen, temperature, and precipitation in Tulsa, Oklahoma over 25 to 34 years. Pollen was monitored with a Hirst-type spore trap on the roof of a building at the University of Tulsa and meteorology data were obtained from the National Weather Service. Changes in total pollen intensity were examined along with detailed analyses of the eight most abundant pollen types in the Tulsa atmosphere. In addition to pollen intensity, changes in pollen season start date, end date, peak date and season duration were also analyzed. Results show a trend to increasing temperatures with a significant increase in annual maximum temperature. There was a non-significant trend toward increasing total pollen and a significant increase in tree pollen over time. Several individual taxa showed significant increases in pollen intensity over the study period including spring Cupressaceae and Quercus pollen, while Ambrosia pollen showed a significant decrease. Data from the current study also indicated that the pollen season started earlier for spring pollinating trees and Poaceae. Significant correlations with preseason temperature may explain the earlier pollen season start dates along with a trend toward increasing March temperatures. More research is needed to understand the global impact of climate change on allergenic species, especially from other regions that have not been studied.

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Tornadoes with Cold Core 500-mb Lows

Weather and Forecasting ◽

10.1175/waf967.1 ◽

2006 ◽

Vol 21 (6) ◽

pp. 1051-1062 ◽

Cited By ~ 7

Author(s):

Jonathan M. Davies

Keyword(s):

United States ◽

Severe Weather ◽

Surface Heating ◽

Vertical Shear ◽

Cold Temperatures ◽

Low Level ◽

Close Proximity ◽

Central United States ◽

Surface Patterns ◽

Cold Core

Abstract Tornadoes that occur in close proximity to midlevel closed lows with a core of cold temperatures aloft are not uncommon, particularly in the central United States. Although several informal studies have shown that severe weather and tornadoes can occur with these midlevel lows, little in the way of formal work has been published documenting features and ingredients of such systems, especially those that produce what are sometimes called cold core tornadoes. Of particular concern is that these tornadoes can be associated with surface and low-level moisture that appears deceptively small or marginal regarding severe weather potential, yet on occasion tornadoes of F2 or greater intensity can develop. In other cases, vertical shear may appear relatively weak at locations close to the midlevel low, suggesting little potential for tornadoes. These “atypical” characteristics can result in poor anticipation by forecasters of tornado events associated with closed 500-mb lows. This note documents some synoptic and mesoscale features commonly associated with tornado events in close proximity to cold core 500-mb lows using four tornadic cases in Kansas as examples, including photographs to show the small nature of storms associated with such systems. Recognition of surface patterns with a particular organization of boundaries and surface heating positioned near midlevel lows, along with the presence of some amount of buoyancy, can help with the operational awareness of the potential for tornadoes in many 500-mb closed low settings.

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Low-Level Jets in the North American Regional Reanalysis (NARR): A Comparison with Rawinsonde Observations

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-13-0364.1 ◽

2014 ◽

Vol 53 (9) ◽

pp. 2093-2113 ◽

Cited By ~ 21

Author(s):

Claudia K. Walters ◽

Julie A. Winkler ◽

Sara Husseini ◽

Ryan Keeling ◽

Jovanka Nikolic ◽

...

Keyword(s):

Temporal Resolution ◽

North American ◽

Low Level ◽

The North ◽

Central United States ◽

North American Regional Reanalysis ◽

Low Level Jets ◽

Regional Reanalysis ◽

Wind Profiles ◽

Fine Resolution

AbstractClimatological analyses of low-level jets (LLJs) can be negatively influenced by the coarse spatial and temporal resolution and frequent changes in observing and archiving protocols of rawinsonde observations (raobs). The introduction of reanalysis datasets, such as the North American Regional Reanalysis (NARR), provides new resources for climatological research with finer spatial and temporal resolution and potentially fewer inhomogeneities. To assess the compatibility of LLJ characteristics identified from NARR wind profiles with those obtained from raob profiles, LLJs were extracted using standard jet definitions from NARR and raobs at 12 locations in the central United States for four representative years that reflect different rawinsonde protocols. LLJ characteristics (e.g., between-station differences in relative frequency, diurnal fluctuations, and mean speed and elevation) are generally consistent, although absolute frequencies are smaller for NARR relative to raobs at most stations. LLJs are concurrently identified in the NARR and raob wind profiles on less than 60% of the observation times with LLJ activity. Variations are seen between analysis years and locations. Of particular note is the substantial increase in LLJ frequency seen in raobs since the introduction of the Radiosonde Replacement System, which has led to a greater discrepancy in jet frequency between the NARR and raob datasets. The analyses suggest that NARR is a viable additional resource for climatological analyses of LLJs. Many of the findings are likely applicable for other fine-resolution reanalysis datasets, although differences between reanalyses require that each be carefully evaluated before its use in climatological analyses of wind maxima.

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Hydrodynamics of the Caribbean Low-Level Jet and Its Relationship to Precipitation

Journal of Climate ◽

10.1175/2009jcli3210.1 ◽

2010 ◽

Vol 23 (6) ◽

pp. 1477-1494 ◽

Cited By ~ 79

Author(s):

Kerry H. Cook ◽

Edward K. Vizy

Keyword(s):

United States ◽

South America ◽

The United States ◽

Caribbean Basin ◽

Low Level ◽

The North ◽

South Central ◽

Central United States ◽

Low Level Jet ◽

The Caribbean

Abstract The easterly Caribbean low-level jet (CLLJ) is a prominent climate feature over the Intra-America Seas, and it is associated with much of the water vapor transport from the tropical Atlantic into the Caribbean Basin. In this study, the North American Regional Reanalysis (NARR) is analyzed to improve the understanding of the dynamics of the CLLJ and its relationship to regional rainfall variations. Horizontal momentum balances are examined to understand how jet variations on both diurnal and seasonal time scales are controlled. The jet is geostrophic to the first order. Its previously documented semidiurnal cycle (with minima at about 0400 and 1600 LT) is caused by semidiurnal cycling of the meridional geopotential height gradient in association with changes in the westward extension of the North Atlantic subtropical high (NASH). A diurnal cycle is superimposed, associated with a meridional land–sea breeze (solenoidal circulation) onto the north coast of South America, so that the weakest jet velocities occur at 1600 LT. The CLLJ is present throughout the year, and it is known to vary in strength semiannually. Peak magnitudes in July are related to the seasonal cycle of the NASH, and a second maximum in February is caused by heating over northern South America. From May through September, zonal geopotential gradients associated with summer heating over Central America and Mexico induce meridional flow. The CLLJ splits into two branches, including a southerly branch that connects with the Great Plains low-level jet (GPLLJ) bringing moisture into the central United States. During the rest of the year, the flow remains essentially zonal across the Caribbean Basin and into the Pacific. A strong (weak) CLLJ is associated with reduced (enhanced) rainfall over the Caribbean Sea throughout the year in the NARR. The relationship with precipitation over land depends on the season. Despite the fact that the southerly branch of the CLLJ feeds into the meridional GPLLJ in May through September, variations in the CLLJ strength during these months do not impact U.S. precipitation, because the CLLJ strength is varying in response to regional-scale forcing and not to changes in the large-scale circulation. During the cool season, there are statistically significant correlations between the CLLJ index and rainfall over the United States. When the CLLJ is strong, there is anomalous northward moisture transport across the Gulf of Mexico into the central United States and pronounced rainfall increases over Louisiana and Texas. A weak jet is associated with anomalous westerly flow across the southern Caribbean region and significantly reduced rainfall over the south-central United States. No connection between the intensity of the CLLJ and drought over the central United States is found. There are only three drought summers in the NARR period (1980, 1988, and 2006), and the CLLJ was extremely weak in 1988 but not in 1980 or 2006.

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The Low-Level Structure and Evolution of a Dry Arctic Front over the Central United States. Part II: Comparison with Theory

Monthly Weather Review ◽

10.1175/1520-0493(1996)124<1676:tllsae>2.0.co;2 ◽

1996 ◽

Vol 124 (8) ◽

pp. 1676-1692 ◽

Cited By ~ 5

Author(s):

William Blumen ◽

Nimal Gamage ◽

Robert L. Grossman ◽

Margaret A. LeMone ◽

L. Jay Miller

Keyword(s):

United States ◽

Level Structure ◽

Low Level ◽

Central United States ◽

Arctic Front

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Understanding recurrent land use processes and long-term transitions in the dynamic south-central United States, c. 1800 to 2006

Land Use Policy ◽

10.1016/j.landusepol.2017.07.061 ◽

2017 ◽

Vol 68 ◽

pp. 345-354 ◽

Cited By ~ 2

Author(s):

Mark A. Drummond ◽

Glenn E. Griffith ◽

Roger F. Auch ◽

Michael P. Stier ◽

Janis L. Taylor ◽

...

Keyword(s):

United States ◽

Land Use ◽

South Central ◽

Central United States

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A Water Balance–Based, Spatiotemporal Evaluation of Terrestrial Evapotranspiration Products across the Contiguous United States

Journal of Hydrometeorology ◽

10.1175/jhm-d-17-0186.1 ◽

2018 ◽

Vol 19 (5) ◽

pp. 891-905 ◽

Cited By ~ 3

Author(s):

Elizabeth Carter ◽

Christopher Hain ◽

Martha Anderson ◽

Scott Steinschneider

Keyword(s):

United States ◽

Energy Balance ◽

Interannual Variability ◽

Water Budget ◽

Water Budgets ◽

Central United States ◽

Precipitation Estimates ◽

Terrestrial Water ◽

Gauged Basins

Abstract Accurate gridded estimates of evapotranspiration (ET) are essential to the analysis of terrestrial water budgets. In this study, ET estimates from three gridded energy balance–based products (ETEB) with independent model formations and data forcings are evaluated for their ability to capture long-term climatology and interannual variability in ET derived from a terrestrial water budget (ETWB) for 671 gauged basins across the contiguous United States. All three ETEB products have low spatial bias and accurately capture interannual variability of ETWB in the central United States, where ETEB and ancillary estimates of change in total surface water storage (ΔTWS) from the GRACE satellite project appear to close terrestrial water budgets. In humid regions, ETEB products exhibit higher long-term bias, and the covariability of ETEB and ETWB decreases significantly. Several factors related to either failure of ETWB, such as errors in ΔTWS and precipitation, or failure of ETEB, such as treatment of snowfall and horizontal heat advection, explain some of these discrepancies. These results mirror and build on conclusions from other studies: on interannual time scales, ΔTWS and error in precipitation estimates are nonnegligible uncertainties in ET estimates based on a terrestrial water budget, and this confounds their comparison to energy balance ET models. However, there is also evidence that in at least some regions, climate and landscape features may also influence the accuracy and long-term bias of ET estimates from energy balance models, and these potential errors should be considered when using these gridded products in hydrologic applications.

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