scholarly journals Climatology and Meteorological Evolution of Major Wildfire Events over the Northeast United States

2013 ◽  
Vol 28 (1) ◽  
pp. 175-193 ◽  
Author(s):  
Joseph B. Pollina ◽  
Brian A. Colle ◽  
Joseph J. Charney
Keyword(s):  
United States ◽  
Coastal Plain ◽  
Large Scale ◽  
Trajectory Analysis ◽  
Synoptic Pattern ◽  
Pressure System ◽  
Northeast United States ◽  
The North ◽  
North American Regional Reanalysis ◽  
Regional Reanalysis

Abstract This study presents a spatial and temporal climatology of major wildfire events, defined as >100 acres burned (>40.47 ha, where 1 ha = 2.47 acre), in the northeast United States from 1999 to 2009 and the meteorological conditions associated with these events. The northeast United States is divided into two regions: region 1 is centered over the higher terrain of the northeast United States and region 2 is primarily over the coastal plain. About 59% of all wildfire events in these two regions occur in April and May, with ~76% in region 1 and ~53% in region 2. There is large interannual variability in wildfire frequency, with some years having 4–5 times more fire events than other years. The synoptic flow patterns associated with northeast United States wildfires are classified using the North American Regional Reanalysis. The most common synoptic pattern for region 1 is a surface high pressure system centered over the northern Appalachians, which occurred in approximately 46% of all events. For region 2, the prehigh anticyclone type extending from southeast Canada and the Great Lakes to the northeast United States is the most common pattern, occurring in about 46% of all events. A trajectory analysis highlights the influence of large-scale subsidence and decreasing relative humidity during the events, with the prehigh pattern showing the strongest subsidence and downslope drying in the lee of the Appalachians.

scholarly journals Representation of Terrestrial Hydrology and Large-Scale Drought of the Continental United States from the North American Regional Reanalysis

2012 ◽  
Vol 13 (3) ◽  
pp. 856-876 ◽  
Author(s):  
Justin Sheffield ◽  
Ben Livneh ◽  
Eric F. Wood
Keyword(s):  
United States ◽  
Soil Moisture ◽  
North American ◽  
Land Surface ◽  
Large Scale ◽  
State Of The Art ◽  
Vic Model ◽  
The North ◽  
North American Regional Reanalysis ◽  
Regional Reanalysis

Abstract The North American Regional Reanalysis (NARR) is a state-of-the-art land–atmosphere reanalysis product that provides improved representation of the terrestrial hydrologic cycle compared to previous global reanalyses, having the potential to provide an enhanced picture of hydrologic extremes such as floods and droughts and their driving mechanisms. This is partly because of the novel assimilation of observed precipitation, state-of-the-art land surface scheme, and higher spatial resolution. NARR is evaluated in terms of the terrestrial water budget and its depiction of drought at monthly to annual time scales against two offline land surface model [Noah v2.7.1 and Variable Infiltration Capacity (VIC)] simulations and observation-based runoff estimates over the continental United States for 1979–2003. An earlier version of the Noah model forms the land component of NARR and so the offline simulation provides an opportunity to diagnose NARR land surface variables independently of atmospheric feedbacks. The VIC model has been calibrated against measured streamflow and so provides a reasonable estimate of large-scale evapotranspiration. Despite similar precipitation, there are large differences in the partitioning of precipitation into evapotranspiration and runoff. Relative to VIC, NARR and Noah annual evapotranspiration is biased high by 28% and 24%, respectively, and the runoff ratios are 50% and 40% lower. This is confirmed by comparison with observation-based runoff estimates from 1130 small, relatively unmanaged basins across the continental United States. The overestimation of evapotranspiration by NARR is largely attributed to the evapotranspiration component of the Noah model, whereas other factors such as atmospheric forcings or biases induced by precipitation assimilation into NARR play only a minor role. A combination of differences in the parameterization of evapotranspiration and in particular low stomatal resistance values in NARR, the seasonality of vegetation characteristics, the near-surface radiation and meteorology, and the representation of soil moisture dynamics, including high infiltration rates and the relative coupling of soil moisture with baseflow in NARR, are responsible for the differences in the water budgets. Large-scale drought as quantified by soil moisture percentiles covaries closely over the continental United States between the three datasets, despite large differences in the seasonal water budgets. However, there are large regional differences, especially in the eastern United States where the VIC model shows higher variability in drought dynamics. This is mostly due to increased frequency of completely dry conditions in NARR that result from differences in soil depth, higher evapotranspiration, early snowmelt, and early peak runoff. In the western United States, differences in the precipitation forcing contribute to large discrepancies between NARR and Noah/VIC simulations in the representation of the early 2000s drought.

Recurrent Supersynoptic Evolution of the Great Plains Low-Level Jet

2011 ◽  
Vol 24 (2) ◽  
pp. 575-582 ◽  
Author(s):  
Scott J. Weaver ◽  
Sumant Nigam
Keyword(s):  
Great Plains ◽  
Large Scale ◽  
Large Scale Circulation ◽  
Low Level ◽  
The North ◽  
Analysis Strategy ◽  
Precipitation Anomalies ◽  
North American Regional Reanalysis ◽  
Low Level Jet ◽  
Regional Reanalysis

Abstract The evolution of supersynoptic (i.e., pentad) Great Plains low-level jet (GPLLJ) variability, its precipitation impacts, and large-scale circulation context are analyzed in the North American Regional Reanalysis (NARR)—a high-resolution precipitation-assimilating dataset—and the NCEP–NCAR reanalysis. The analysis strategy leans on the extended EOF technique, which targets both spatial and temporal recurrence of a variability episode. Pentad GPLLJ variability structures are found to be spatially similar to those in the monthly analysis. The temporal evolution of the supersynoptic GPLLJ-induced precipitation anomalies reveal interesting lead and lag relationships highlighted by GPLLJ variability-leading precipitation anomalies. Interestingly, similar temporal phasing of the GPLLJ and precipitation anomalies were operative during the 1993 (1988) floods (drought) over the Great Plains, indicating the importance of these submonthly GPLLJ variability modes in the instigation of extreme hydroclimatic episodes. The northward-shifted (dry) GPLLJ variability mode is linked to large-scale circulation variations emanating from remote regions that are modified by interaction with the Rocky Mountains, suggesting that the supersynoptic GPLLJ fluctuations may have their origin in orographic modulation of baroclinic development.

A Brief Evaluation of Precipitation from the North American Regional Reanalysis

2007 ◽  
Vol 8 (4) ◽  
pp. 837-846 ◽  
Author(s):  
Melissa S. Bukovsky ◽  
David J. Karoly
Keyword(s):  
United States ◽  
Spatial Distribution ◽  
Diurnal Cycle ◽  
Annual Cycle ◽  
North American ◽  
The United States ◽  
The Other ◽  
The North ◽  
North American Regional Reanalysis ◽  
Regional Reanalysis

Abstract Several aspects of the precipitation climatology from the North American Regional Reanalysis (NARR) are analyzed and compared with two other reanalyses and one set of gridded observations over a domain encompassing the United States. The spatial distribution, diurnal cycle, and annual cycle of precipitation are explored to establish the reliability of the reanalyses and to judge their usefulness. While the NARR provides a much improved representation of precipitation over that of the other reanalyses examined, some inaccuracies are found and have been highlighted as a warning to potential users of the data.

scholarly journals Understanding the Characteristics of Daily Precipitation over the United States Using the North American Regional Reanalysis

2009 ◽  
Vol 22 (23) ◽  
pp. 6268-6286 ◽  
Author(s):  
Emily J. Becker ◽  
Ernesto Hugo Berbery ◽  
R. Wayne Higgins
Keyword(s):  
United States ◽  
Extreme Events ◽  
Daily Precipitation ◽  
Precipitable Water ◽  
Moisture Flux ◽  
The United States ◽  
Moisture Flux Convergence ◽  
The North ◽  
North American Regional Reanalysis ◽  
Regional Reanalysis

Abstract This study examines the seasonal characteristics of daily precipitation over the United States using the North American Regional Reanalysis (NARR). To help understand the physical mechanisms that contribute to changes in the characteristics of daily precipitation, vertically integrated moisture flux convergence (MFC) and precipitable water were included in the study. First, an analysis of the NARR precipitation was carried out because while observed precipitation is indirectly assimilated in the system, differences exist. The NARR mean seasonal amount is very close to that of observations throughout the year, although NARR exhibits a slight systematic bias toward more-frequent, lighter precipitation. Particularly during summer, the precipitation intensity and the probability distribution function (PDF) indicate that NARR somewhat underestimates extremes and overestimates lighter events in the eastern half of the United States. The intensity and PDF of moisture flux convergence exhibit a strong similarity to those of precipitation, suggesting a link between strong MFC and precipitation extremes. On the other hand, the relationship between the precipitable water and precipitation PDFs is weaker, based on the lack of agreement of their gamma distribution parameters. The dependence of the precipitation PDF on the lower-frequency modulation of ENSO was examined. During El Niño winters, the Southwest and central United States, Gulf of Mexico region, and southeastern coast have greater precipitation intensity and extremes than during La Niña, and the Ohio River and Red River basins have lower intensity and fewer extreme events. During summer, the northern Rocky Mountains receive higher intensity precipitation with more extreme events. Most areas where the change in the daily mean precipitation between ENSO phases is large have greater shifts in the extreme tail of the PDF. The ENSO-related response of moisture flux convergence is similar to that of precipitation. ENSO-related shifts in the precipitation PDF do not appear to have a strong relationship to the shifts in precipitable water.

scholarly journals Trends in Wind Speed at Wind Turbine Height of 80 m over the Contiguous United States Using the North American Regional Reanalysis (NARR)

2012 ◽  
Vol 51 (12) ◽  
pp. 2188-2202 ◽  
Author(s):  
Eric Holt ◽  
Jun Wang
Keyword(s):  
United States ◽  
Wind Speed ◽  
Wind Turbine ◽  
Power Law ◽  
North American ◽  
The North ◽  
Spatial Coverage ◽  
Increasing Trend ◽  
North American Regional Reanalysis ◽  
Regional Reanalysis

AbstractThe trends in wind speed at a typical wind turbine hub height (80 m) are analyzed using the North American Regional Reanalysis (NARR) dataset for 1979–2009. A method, assuming the wind profile in the lower boundary layer as power-law functions of altitude, is developed to invert the power exponent (in the power-law equation) from the NARR data and to compute the following variables at 80 m that are needed for the estimation and interpretation of the trend in wind speed: air density, zonal wind u, meridional wind υ, and wind speed. Statistically significant and positive annual trends are found to be predominant over the contiguous United States, with spring and winter being the two largest contributing seasons. Positive trends in surface wind speed are generally smaller than those at 80 m, with less spatial coverage, reflecting stronger increases in wind speed at altitudes above the 80-m level. Large and positive trends in winds over the southeastern region and high-mountain region are primarily due to the increasing trend in southerly wind, while the trends over the northern states (near the Canadian border) are primarily due to the increasing trend in westerly wind. Trends in the 90th percentile of the annual wind speed, a better indicator for the trend in wind power recourses, are 40%–50% larger than but geographically similar to the trends in the annual mean wind speed. The probable climatic drivers for change in wind speed and direction are discussed, and further studies are needed to evaluate the fidelity of wind speed and direction in the NARR.

Spurious Grid-Scale Precipitation in the North American Regional Reanalysis

2007 ◽  
Vol 135 (6) ◽  
pp. 2168-2184 ◽  
Author(s):  
Gregory L. West ◽  
W. James Steenburgh ◽  
William Y. Y. Cheng
Keyword(s):  
North American ◽  
Prediction Models ◽  
Weather Prediction ◽  
Regional Climate ◽  
Potential Temperature ◽  
Climate Data ◽  
The North ◽  
North American Regional Reanalysis ◽  
Upper Level ◽  
Regional Reanalysis

Abstract Spurious grid-scale precipitation (SGSP) occurs in many mesoscale numerical weather prediction models when the simulated atmosphere becomes convectively unstable and the convective parameterization fails to relieve the instability. Case studies presented in this paper illustrate that SGSP events are also found in the North American Regional Reanalysis (NARR) and are accompanied by excessive maxima in grid-scale precipitation, vertical velocity, moisture variables (e.g., relative humidity and precipitable water), mid- and upper-level equivalent potential temperature, and mid- and upper-level absolute vorticity. SGSP events in environments favorable for high-based convection can also feature low-level cold pools and sea level pressure maxima. Prior to 2003, retrospectively generated NARR analyses feature an average of approximately 370 SGSP events annually. Beginning in 2003, however, NARR analyses are generated in near–real time by the Regional Climate Data Assimilation System (R-CDAS), which is identical to the retrospective NARR analysis system except for the input precipitation and ice cover datasets. Analyses produced by the R-CDAS feature a substantially larger number of SGSP events with more than 4000 occurring in the original 2003 analyses. An oceanic precipitation data processing error, which resulted in a reprocessing of NARR analyses from 2003 to 2005, only partially explains this increase since the reprocessed analyses still produce approximately 2000 SGSP events annually. These results suggest that many NARR SGSP events are not produced by shortcomings in the underlying Eta Model, but by the specification of anomalous latent heating when there is a strong mismatch between modeled and assimilated precipitation. NARR users should ensure that they are using the reprocessed NARR analyses from 2003 to 2005 and consider the possible influence of SGSP on their findings, particularly after the transition to the R-CDAS.

Seasonal Predictability of Wintertime mid-latitude Cyclonic Activity over the North Atlantic and Europe

2021 ◽  
Author(s):  
Alvise Aranyossy ◽  
Sebastian Brune ◽  
Lara Hellmich ◽  
Johanna Baehr
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Jet Stream ◽  
Cyclonic Activity ◽  
Max Planck ◽  
Pressure System ◽  
Wind Speeds ◽  
Average Lifespan ◽  
The North ◽  
The North Atlantic

<p>We analyse the connections between the wintertime North Atlantic Oscillation (NAO), the eddy-driven jet stream with the mid-latitude cyclonic activity over the North Atlantic and Europe. We investigate, through the comparison against ECMWF ERA5 and hindcast simulations from the Max Planck Institute Earth System Model (MPI-ESM), the potential for enhancement of the seasonal prediction skill of the Eddy Kinetic Energy (EKE) by accounting for the connections between large-scale climate and the regional cyclonic activity. Our analysis focuses on the wintertime months (December-March) in the 1979-2019 period, with seasonal predictions initialized every November 1st. We calculate EKE from wind speeds at 250 hPa, which we use as a proxy for cyclonic activity. The zonal and meridional wind speeds are bandpass filtered with a cut-off at 3-10 days to fit with the average lifespan of mid-latitude cyclones. </p><p>Preliminary results suggest that in ERA5, major positive anomalies in EKE, both in quantity and duration, are correlated with a northern position of the jet stream and a positive phase of the NAO. Apparently, a deepened Icelandic low-pressure system offers favourable conditions for mid-latitude cyclones in terms of growth and average lifespan. In contrast, negative anomalies in EKE over the North Atlantic and Central Europe are associated with a more equatorward jet stream, these are also linked to a negative phase of the NAO.  Thus, in ERA5, the eddy-driven jet stream and the NAO play a significant role in the spatial and temporal distribution of wintertime mid-latitude cyclonic activity over the North Atlantic and Europe. We extend this connection to the MPI-ESM hindcast simulations and present an analysis of their predictive skill of EKE for wintertime months.</p>

scholarly journals North American Supercell Environments in Atmospheric Reanalyses and RUC-2

2019 ◽  
Vol 58 (1) ◽  
pp. 71-92 ◽  
Author(s):  
Austin T. King ◽  
Aaron D. Kennedy
Keyword(s):  
North American ◽  
Grid Point ◽  
Convective Available Potential Energy ◽  
Kinematic Parameters ◽  
The North ◽  
Composite Parameter ◽  
Analysis Package ◽  
North American Regional Reanalysis ◽  
Regional Reanalysis ◽  
Effective Layer

AbstractA suite of modern atmospheric reanalyses is analyzed to determine how they represent North American supercell environments. This analysis is performed by comparing a database of Rapid Update Cycle (RUC-2) proximity soundings with profiles derived from the nearest grid point in each reanalysis. Parameters are calculated using the Sounding and Hodograph Analysis and Research Program in Python (SHARPpy), an open-source Python sounding-analysis package. Representation of supercell environments varies across the reanalyses, and the results have ramifications for climatological studies that use these datasets. In particular, thermodynamic parameters such as the convective available potential energy (CAPE) show the widest range in biases, with reanalyses falling into two camps. The North American Regional Reanalysis (NARR) and the Japanese 55-year Reanalysis (JRA-55) are similar to RUC-2, but other reanalyses have a substantial negative bias. The reasons for these biases vary and range from thermodynamic biases at the surface to evidence of convective contamination. Overall, it is found that thermodynamic biases feed back to other convective parameters that incorporate CAPE directly or indirectly via the effective layer. As a result, significant negative biases are found for indices such as the supercell composite parameter. These biases are smallest for NARR and JRA-55. Kinematic parameters are more consistent across the reanalyses. Given the issues with thermodynamic properties, better segregation of soundings by storm type is found for fixed-layer parameters than for effective-layer shear parameters. Although no reanalysis can exactly reproduce the results of earlier RUC-2 studies, many of the reanalyses can broadly distinguish between environments that are significantly tornadic versus nontornadic.

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