The Pacific/ North American Teleconnection Pattern and United States Climate. Part I: Regional Temperature and Precipitation Associations

The Pacific/ North American (PNA) teleconnection index, a measure of the strength and phase of the PNA teleconnection pattern, is related to the variations of the surface climate of the United States from 1947 through 1982 for the autumn, winter, and spring months when the PNA is a main mode of Northern Hemisphere mid-tropospheric variability. The results demonstrate that the PNA index is highly correlated with both regional temperature and precipitation. The strongest, most extensive correlations between the index and temperature are observed in winter, but large areas of the country show important associations during the spring and autumn as well. Although the centers of highest correlation migrate systematically with changes in the circumpolar vortex over the course of the annual cycle, the southeastern and northwestern parts of the United States possess consistently high index- temperature correlations. Correlations between the PNA index and precipitation are weaker and less extensive than those for temperature, but large coherent regions of high correlations are observed across the nation. Winter and early spring exhibit the strongest relationships because spatially coherent synoptic-scale systems, related to the long-wave pattern, control precipitation. The late spring and early autumn seasons have the least extensive and weakest correlations due to the importance of less organized smaller-scale convective rainfall events

Discharge responses associated with rapid snow cover ablation events in the Susquehanna and Wabash River basins

In the mid-latitudes, snow plays a critical role in regional hydroclimate, with snow ablation variability in ephemeral regions representing an area of essential research. Due to a lack of historical snow-water-equivalent data in the eastern United States, recent research has substituted daily snow depth changes for ablation. These studies, however, do not explicitly examine if such a substitution yields a snowmelt hydrological signal, an important component of water resource management. As such, this study evaluates if ablation events, as defined as a daily snow depth decrease, subsequently result in increased river discharge within two similarly sized watersheds in the eastern United States: the Wabash and Susquehanna River basins. For both basins, \u3e75% of snow ablation events resulted in a positive river discharge response (increase in discharge) at a 3-day lag. Furthermore, results show a significant and positive relationship between ablation event frequency and seasonal discharge response, such that an increase (decrease) in seasonal snow ablation event frequency yields an increase (decrease) in associated seasonal river discharge at a 3-day lag. These relationships indicate that inter-diurnal decreases in snow depth do carry hydrological implications, adding confidence that such a definition of ablation is appropriate for climatological applications

Climatology of the daily temperature range annual cycle in the United States

Many researchers are presently interested in detecting long-term trends in annual or seasonal daily temperature range (DTR), and attributing these changes to anthropogenic origins. However, very little work has been done to confirm the mechanisms that are important to determining the long-term average annual cycle of the DTR. Therefore, the focus of this work is to examine the spatial and temporal difference in the DTR average annual cycle across the United States, and to associate the patterns of these cycles with potential causal variables. Three major types of DTR annual cycle exist in the United States: high sun season maximum (northern and western U.S.), low sun season maximum (south central and southeast U.S.), and transitional season maxima (middle latitude in the U.S.). The annual cycles of the DTR in the northern and western U.S. are well related to average annual cycles of cloud cover and dew point temperature; only areas to the west of the Rocky Mountains have a strong linkage between DTR and precipitation frequency annual cycles. Across the northern tier of the U.S., the loss of snow cover is important to DTR transitions during the spring season. However, the onset of snow cover in the fall does not appear to be the major factor in DTR variations, which are instead more strongly associated with cloud cover effects. As expected from their sinusoidal annual cycle, maximum and minimum temperature cycles are linearly related to the DTR in regions with a warm season or cold season DTR maximum, while non-linear relationships exist where the DTR annual cycle has maxima in the transition seasons

Effect of remote ischaemic conditioning on clinical outcomes in patients with acute myocardial infarction (CONDI-2/ERIC-PPCI): a single-blind randomised controlled trial.

BACKGROUND: Remote ischaemic conditioning with transient ischaemia and reperfusion applied to the arm has been shown to reduce myocardial infarct size in patients with ST-elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PPCI). We investigated whether remote ischaemic conditioning could reduce the incidence of cardiac death and hospitalisation for heart failure at 12 months. METHODS: We did an international investigator-initiated, prospective, single-blind, randomised controlled trial (CONDI-2/ERIC-PPCI) at 33 centres across the UK, Denmark, Spain, and Serbia. Patients (age >18 years) with suspected STEMI and who were eligible for PPCI were randomly allocated (1:1, stratified by centre with a permuted block method) to receive standard treatment (including a sham simulated remote ischaemic conditioning intervention at UK sites only) or remote ischaemic conditioning treatment (intermittent ischaemia and reperfusion applied to the arm through four cycles of 5-min inflation and 5-min deflation of an automated cuff device) before PPCI. Investigators responsible for data collection and outcome assessment were masked to treatment allocation. The primary combined endpoint was cardiac death or hospitalisation for heart failure at 12 months in the intention-to-treat population. This trial is registered with ClinicalTrials.gov (NCT02342522) and is completed. FINDINGS: Between Nov 6, 2013, and March 31, 2018, 5401 patients were randomly allocated to either the control group (n=2701) or the remote ischaemic conditioning group (n=2700). After exclusion of patients upon hospital arrival or loss to follow-up, 2569 patients in the control group and 2546 in the intervention group were included in the intention-to-treat analysis. At 12 months post-PPCI, the Kaplan-Meier-estimated frequencies of cardiac death or hospitalisation for heart failure (the primary endpoint) were 220 (8·6%) patients in the control group and 239 (9·4%) in the remote ischaemic conditioning group (hazard ratio 1·10 [95% CI 0·91-1·32], p=0·32 for intervention versus control). No important unexpected adverse events or side effects of remote ischaemic conditioning were observed. INTERPRETATION: Remote ischaemic conditioning does not improve clinical outcomes (cardiac death or hospitalisation for heart failure) at 12 months in patients with STEMI undergoing PPCI. FUNDING: British Heart Foundation, University College London Hospitals/University College London Biomedical Research Centre, Danish Innovation Foundation, Novo Nordisk Foundation, TrygFonden

Relationships between 700 mb Circulation Variations and Great Plains Climate

The relationship between monthly midtropospheric circulation variations, occurring in the North American sector, and surface temperature and precipitation across the Great Plains is evaluated for the middle month of each season (January, April, July, and October). The results demonstrate that monthly Great Plains temperature variability is strongly associated with the major pattems of midtropospheric circulation variation during all months considered. Temporally, the strongest associations are observed during October. However, January, July, and April also exhibit spatially coherent regions of strong association. Spatially, the relationship tends to be strongest in the northern Plains, with decreasing association to the south. Precipitation-midtroposphere relationships are weaker than those for temperature during all months. The association between the midtroposphere and precipitation is relatively strong from late fall through late spring. However, the convective nature of precipitation in the region during the summer months limits any strong relationships in July. In a spatial sense, no preferred regions of precipitation explanation were indicated in the analysis

The Pacific/ North American Teleconnection Pattern and United States Climate. Part I: Regional Temperature and Precipitation Associations

The Pacific/ North American (PNA) teleconnection index, a measure of the strength and phase of the PNA teleconnection pattern, is related to the variations of the surface climate of the United States from 1947 through 1982 for the autumn, winter, and spring months when the PNA is a main mode of Northern Hemisphere mid-tropospheric variability. The results demonstrate that the PNA index is highly correlated with both regional temperature and precipitation. The strongest, most extensive correlations between the index and temperature are observed in winter, but large areas of the country show important associations during the spring and autumn as well. Although the centers of highest correlation migrate systematically with changes in the circumpolar vortex over the course of the annual cycle, the southeastern and northwestern parts of the United States possess consistently high index- temperature correlations. Correlations between the PNA index and precipitation are weaker and less extensive than those for temperature, but large coherent regions of high correlations are observed across the nation. Winter and early spring exhibit the strongest relationships because spatially coherent synoptic-scale systems, related to the long-wave pattern, control precipitation. The late spring and early autumn seasons have the least extensive and weakest correlations due to the importance of less organized smaller-scale convective rainfall events

Climatology of the daily temperature range annual cycle in the United States

Many researchers are presently interested in detecting long-term trends in annual or seasonal daily temperature range (DTR), and attributing these changes to anthropogenic origins. However, very little work has been done to confirm the mechanisms that are important to determining the long-term average annual cycle of the DTR. Therefore, the focus of this work is to examine the spatial and temporal difference in the DTR average annual cycle across the United States, and to associate the patterns of these cycles with potential causal variables. Three major types of DTR annual cycle exist in the United States: high sun season maximum (northern and western U.S.), low sun season maximum (south central and southeast U.S.), and transitional season maxima (middle latitude in the U.S.). The annual cycles of the DTR in the northern and western U.S. are well related to average annual cycles of cloud cover and dew point temperature; only areas to the west of the Rocky Mountains have a strong linkage between DTR and precipitation frequency annual cycles. Across the northern tier of the U.S., the loss of snow cover is important to DTR transitions during the spring season. However, the onset of snow cover in the fall does not appear to be the major factor in DTR variations, which are instead more strongly associated with cloud cover effects. As expected from their sinusoidal annual cycle, maximum and minimum temperature cycles are linearly related to the DTR in regions with a warm season or cold season DTR maximum, while non-linear relationships exist where the DTR annual cycle has maxima in the transition seasons

Do Storm Synoptic Patterns Affect Biogeochemical Fluxes From Temperate Deciduous Forest Canopies?

The volumetric quantity and biogeochemical quality of throughfall and stemflow in forested ecosystems are influenced by biological characteristics as well environmental and storm meteorological conditions. Previous attempts at connecting forest water and nutrient cycles to storm characteristics have focused on individual meteorological variables, but we propose a unified approach by examining the storm system in its entirety. In this study, we use methods from synoptic climatology to distinguish sub-canopy biogeochemical fluxes between storm events to understand the response of forest ecosystems to daily weather patterns. For solute inputs tied to atmospheric deposition (NH4+, NO3−, SO42−, Na+, Cl−), stagnant air masses resulted in high inputs in rainfall (273.42, 81.81, 52.30, 156.99, 128.70 μmol L−1), throughfall (355.05, 130.66, 83.24, 239.55, 261.32 μmol L−1), and stemflow (338.34, 182.75, 153.74, 125.75, 272.88 μmol L−1). For inputs tied to canopy exchange (DOC, K+, Ca2+, Mg2+), a clear distinction was observed between throughfall and stemflow pathways. The largest throughfall concentrations were in the Great Lakes Low (1794.80, 352.96, 72.75, 74.37 μmol L−1) while the largest stemflow concentrations were in the Weak Upper Trough (3681.78, 497.34, 82.36, 72.46 μmol L−1). Stemflow leaching is likely derived from a larger reservoir of leachable cations in the tree canopy than throughfall, with stemflow fluxes maximized during synoptic types with greater rainfall amounts and throughfall fluxes diluted. For flux-based enrichment ratios, water volume, storm magnitude, antecedent dry period, and seasonality were important factors, further illustrating the influence of synoptic characteristics on wash-off, leaching and, ultimately, dilution processes within the canopy

Identifying Patterns of Forest Hydrologic and Biogeochemical Fluxes Using Weather Map Classification in a Mid-atlantic Deciduous Forest

The partitioning of precipitation within the forest canopy into throughfall and stemflow is controlled by biotic and abiotic factors, which include storm characteristics (e.g., intensity, duration, and magnitude) and canopy structural parameters. Our research uses novel applications of weather map classification to relate synoptic scale weather patterns to the surface environment. A daily synoptic calendar was developed in the Mid-Atlantic (USA) to categorize the subcanopy hydrologic and biogeochemical fluxes during storm events in an eastern deciduous forest. Synoptic classification identified 6 low pressure systems, 4 high pressure systems, 1 cold front, 3 northerly flow regimes, 3 southerly flow regimes, and 5 weak patterns across 4 seasons. The low pressure systems were commonly associated with the largest average flux-based enrichment ratios of solutes in throughfall and stemflow compared to rainfall solute concentrations. Low pressures such as the Weak Coastal Low, centered off the Mid-Atlantic coast with easterly winds over the study region, were associated with large rainfall events with moderate intensities falling over a long period of time. This combination of meteorological conditions allowed complete washoff of antecedent atmospheric deposition and maximum canopy leaching as storm systems of this magnitude were able to wet the entire canopy. The lowest flux-based enrichment ratios occurred during the passage of cold fronts and under weak southwest flow regimes, which were both characterized by moderately high rainfall amounts that occurred over short periods of time (i.e., \u3c 0.5 days) with high intensities (i.e., \u3e 5 mm h-1). As a result, the water from these storm systems passed through the forest canopy very quickly and with minimal contact time thus resulting in minimal enrichment of throughfall and stemflow. The distinct chemical signatures of synoptic types provide evidence that this novel application of storm classification in forest hydrology is useful for estimating hydrologic and nutrient fluxes in eastern forests and modeling forest water and nutrient budgets in response to changing precipitation characteristics in the region