scholarly journals An Updated Synoptic Climatology of Lake Erie and Lake Ontario Heavy Lake-Effect Snow Events

Atmosphere ◽  
2020 ◽  
Vol 11 (8) ◽  
pp. 872
Author(s):  
Jake Wiley ◽  
Andrew Mercer
Keyword(s):  
Composite Structures ◽  
Large Scale ◽  
Wrf Model ◽  
Principal Component ◽  
Synoptic Climatology ◽  
Composite Support ◽  
The North ◽  
Lake Effect ◽  
Upper Level ◽  
Regional Reanalysis

Lake-effect snow (LES) storms pose numerous hazards, including extreme snowfall and blizzard conditions, and insight into the large-scale precursor conditions associated with LES can aid local forecasters and potentially allow risks to be mitigated. In this study, a synoptic climatology of severe LES events over Lakes Erie and Ontario was created using an updated methodology based on previous studies with similar research objectives. Principal component analysis (PCA) coupled with cluster analysis (CA) was performed on a case set of LES events from a study domain encompassing both lakes, grouping LES events with similar spatial characteristics into the primary composite structures for LES. Synoptic scale composites were constructed for each cluster using the North American Regional Reanalysis (NARR). Additionally, one case from each cluster was simulated using the Weather Research and Forecast (WRF) model to analyze mesoscale conditions associated with each of the clusters. Three synoptic setups were identified that consisted of discrepancies, mostly in the surface fields, from a common pattern previously identified as being conducive to LES, which features a dipole and upper-level low pressure anomaly located near the Hudson Bay. Mesoscale conditions associated with each composite support differing LES impacts constrained to individual lakes or a combination of both.

scholarly journals Synoptic Climatology of Lake-Effect Snow Events off the Western Great Lakes

Climate ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 43
Author(s):  
Jake Wiley ◽  
Andrew Mercer
Keyword(s):  
Great Lakes ◽  
Large Scale ◽  
Lake Michigan ◽  
Lake Superior ◽  
Principal Component ◽  
Forecast Model ◽  
Synoptic Climatology ◽  
Synoptic Scale ◽  
Ongoing Research ◽  
Lake Effect

As the mesoscale dynamics of lake-effect snow (LES) are becoming better understood, recent and ongoing research is beginning to focus on the large-scale environments conducive to LES. Synoptic-scale composites are constructed for Lake Michigan and Lake Superior LES events by employing an LES case repository for these regions within the U.S. North American Regional Reanalysis (NARR) data for each LES event were used to construct synoptic maps of dominant LES patterns for each lake. These maps were formulated using a previously implemented composite technique that blends principal component analysis with a k-means cluster analysis. A sample case from each resulting cluster was also selected and simulated using the Advanced Weather Research and Forecast model to obtain an example mesoscale depiction of the LES environment. The study revealed four synoptic setups for Lake Michigan and three for Lake Superior whose primary differences were discrepancies in a surface pressure dipole structure previously linked with Great Lakes LES. These subtle synoptic-scale differences suggested that while overall LES impacts were driven more by the mesoscale conditions for these lakes, synoptic-scale conditions still provided important insight into the character of LES forcing mechanisms, primarily the steering flow and air–lake thermodynamics.

scholarly journals Multi-Reanalysis Climatology of Intermountain Cyclones

2010 ◽  
Vol 138 (11) ◽  
pp. 4035-4053 ◽  
Author(s):  
Matthew E. Jeglum ◽  
W. James Steenburgh ◽  
Tiros P. Lee ◽  
Lance F. Bosart
Keyword(s):  
Sierra Nevada ◽  
Great Basin ◽  
Large Scale ◽  
Intermountain West ◽  
The North ◽  
Evolution Analysis ◽  
Flow Splitting ◽  
Monthly Distribution ◽  
Upper Level ◽  
Regional Reanalysis

Abstract The topography in and around the Intermountain West strongly affects the genesis, migration, and lysis of extratropical cyclones. Here intermountain (i.e., Nevada or Great Basin) cyclone (IC) activity and evolution are examined using the ECMWF Re-Analysis Interim (ERA-Interim) the North American Regional Reanalysis (NARR), and the NCEP–NCAR reanalysis from 1989 to 2008, the period during which all three are available. The ICs are defined and tracked objectively as 850-hPa geopotential height depressions of ≥40 m that persist for ≥12 h. The monthly distribution of IC center and genesis frequency in all three reanalyses is bimodal with spring (absolute) and fall (secondary) maxima. Although the results are sensitive to differences in resolution, topographic representation, and reanalysis methodology, both the ERA-Interim and NARR produce frequent IC centers and genesis in the Great Basin cyclone region, which extends from the southern “high” Sierra to northwest Utah, and the Canyonlands cyclone region, which lies over the upper Colorado River basin of southeast Utah. The NCEP–NCAR reanalysis fails to resolve these two distinct cyclone regions and produces less frequent IC centers and genesis than the ERA-Interim and NARR. An ERA-Interim-based composite of strong ICs generated in cross-Sierra (210°–300°) 500-hPa flow shows that cyclogenesis is preceded by the development of the Great Basin confluence zone (GBCZ), a regional airstream boundary that extends downstream from the Sierra Nevada across the Intermountain West. Cyclogenesis occurs along the GBCZ as large-scale ascent develops over the Intermountain West in advance of an approaching upper-level trough. Flow splitting around the high Sierra and the presence of low-level baroclinicity along the GBCZ suggest that IC evolution may be better conceptualized from a potential vorticity perspective than from traditional quasigeostrophic models of lee cyclogenesis. Although these results provide new insights into IC activity and evolution, analysis uncertainty and the cyclone identification criteria are important sources of ambiguity that cannot be fully eliminated.

scholarly journals The OWLeS IOP2b Lake-Effect Snowstorm: Shoreline Geometry and the Mesoscale Forcing of Precipitation

2017 ◽  
Vol 145 (7) ◽  
pp. 2421-2436 ◽  
Author(s):  
W. James Steenburgh ◽  
Leah S. Campbell
Keyword(s):  
New York ◽  
Large Scale ◽  
Model Simulation ◽  
System Development ◽  
Wrf Model ◽  
Lake Ontario ◽  
Land Breeze ◽  
Primary Role ◽  
The North ◽  
Lake Effect

Long-lake-axis-parallel (LLAP) lake-effect precipitation systems that form when the flow is parallel to the long axis of an elongated body of water frequently produce intense, highly localized snowfall. Conceptual models of these LLAP systems typically emphasize the role of thermally forced land breezes from the flanking shorelines, with low-level convergence and ascent centered near the lake axis. In reality, other factors such as shoreline geometry and differential surface roughness can strongly influence LLAP systems. Here a WRF Model simulation is used to examine the mesoscale forcing of lake-effect precipitation over Lake Ontario during IOP2b of the Ontario Winter Lake-effect Systems (OWLeS) field campaign. In the simulation, the large-scale flow, shoreline geometry, and differential surface heating and roughness contribute to the development of three major airmass boundaries. The first is a land-breeze front that forms along a bulge in the south shoreline between St. Catharines, Ontario, Canada, and Thirty Mile Point, New York; extends downstream over eastern Lake Ontario; and plays a primary role in the LLAP system development. The second is a land-breeze front that forms along the southeast shoreline near Oswego, New York; extends downstream and obliquely across the LLAP system near Tug Hill; and influences inland precipitation processes. The third is a convergence zone that extends downstream from the north shoreline near Point Petre, Ontario, Canada; and contributes to the intermittent development of lake-effect precipitation north of the primary LLAP system. These results highlight the multifaceted nature of LLAP system development over Lake Ontario, especially the contributions of shoreline geometry and mesoscale airmass boundaries.

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.

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.

scholarly journals Barotropic Regeneration of Upper-Level Synoptic Disturbances in Different Configurations of the Zonal Weather Regime

2008 ◽  
Vol 65 (10) ◽  
pp. 3159-3178 ◽  
Author(s):  
Gwendal Rivière
Keyword(s):  
Large Scale ◽  
Deformation Field ◽  
Regeneration Process ◽  
Barotropic Model ◽  
Weather Regime ◽  
The North ◽  
The Difference ◽  
Upper Level ◽  
Composite Maps ◽  
Large Scale Flow

Barotropic dynamics of upper-tropospheric midlatitude disturbances evolving in different configurations of the zonal weather regime (i.e., in different zonal-like large-scale flows) were studied using observational analyses and barotropic model experiments. The contraction stage of upper-level disturbances that follows their elongation stage leads to an increase of eddy kinetic energy that is called the barotropic regeneration process in this text. This barotropic mechanism is studied through notions of barotropic critical regions (BtCRs) and effective deformation that have been introduced in a previous paper. The effective deformation field is equal to the difference between the square of the large-scale deformation magnitude and the square of the large-scale vorticity. Regions where the effective deformation is positive correspond to regions where the large-scale flow tends to strongly stretch synoptic disturbances. A BtCR is an area separating two large-scale regions of positive effective deformation, one located upstream and on the south side of the jet and the other downstream and on the north side. Such a region presents a discontinuity in the orientation of the dilatation axes and is a potential area where the barotropic regeneration process may occur. Winter days presenting a zonal weather regime in the 40-yr ECMWF Re-Analysis dataset are decomposed, via a partitioning algorithm, into different configurations of the effective deformation field at 300 hPa. A six-cluster partition is obtained. Composite maps of the barotropic generation rate for each cluster exhibit a succession of negative and positive values on both sides of the BtCRs. It confirms statistically that the barotropic regeneration mechanism occurs preferentially about BtCRs. Numerical experiments using a forced barotropic model on the sphere are performed. Each experiment consists of adding a synoptic-scale perturbation to one of the zonal-like jet configurations found in observations, which is kept fixed with time. The combined effects of the effective deformation and nonlinearities are shown to be crucial to reproduce the barotropic regeneration process about BtCRs.

scholarly journals The Ancient City of Babylon

2020 ◽  
Vol 2 (40) ◽  
pp. 617-656
Author(s):  
Mohammed S. Mahan ◽  
Ghassan Muslim Hamza
Keyword(s):  
Historical Development ◽  
Large Scale ◽  
Building Materials ◽  
Large City ◽  
Aerial Photos ◽  
The North ◽  
City Gates ◽  
Upper Level ◽  
Materials Used ◽  
The City

       Babylon during Nebuchadnezzar II (604-562 BC) was a great city. It had been a large city since Old Babylonian times, but Nebuchadnezzar’s expansion of the city and large-scale rebuilding of important buildings with good baked brick instead of the traditional unbaked mudbrick created something exceptional. Babylon now was larger than Nineveh had been and larger than any of the cities in the known world. The political and economic base for this development was of course that it was the centre of the Neo-Babylonian empire created by Nebuchadnezzar’s father Nabopolassar (625–605 BC) and succeeding the Neo Assyrian empire as the main political entity in the Middle East.         An attempt for the first time to bring together the main results of the German excavations in Babylon with the main results from the Iraqi excavations there and thereby make use of the available cuneiform documentation and a selected use of the best of the classical tradition. With the help of a GIS software (QGIS) and a BIM program (ArchiCAD) the use of satellite images and aerial photos combined with inspection on the site, the historical development of the site has been studied and a digital research model of Babylon for different periods of the city’s history has been created.          Only main buildings and constructions have been considered and placed in the appropriate historical and archaeological context. Part 1 includes some information about the historical development of buildings and nature in Babylon, the rivers and groundwater in Baybylon, as well as basics about the building materials used in Babylon. Part 2 discuss the city walls and city gates, introductory matters about the history, excavation and other documentations of the walls and gates. The chapter also includes presentation of the walls and gates during Nabopolassar followed by a detailed discussion of the walls and gates during Nebuchadnezzar. The Ištar gate and the area around it with the different levels and the upper level glazed decoration have been treated separately. Detailed interpretations about the palaces, development of the main traditional South Palace and the new constructed North are discussed in part 3. Reasonable suggestions for the Hanging Gardens in the North Palace have be provided.          The temples are discussed in part 4 detailing the Marduk temple and the zikkurrat. The historical development of the four temples reconstructed on the site in Babylon on their old foundations, i.e. Nabû, Ištar, Ašratum, and Ninmaḫ temples, is discussed with indication which levels have been used for the reconstructions. The historical development of the other excavated temples, i.e. the Ninurta and Išḫara temples, are discussed in a similar way. Attention will be paid to the remains of wall decorations in the temples.  

scholarly journals Contrasting stable water isotope signals from convective and large-scale precipitation phases of a heavy precipitation event in southern Italy during HyMeX IOP 13: a modelling perspective

2019 ◽  
Vol 19 (11) ◽  
pp. 7487-7506
Author(s):  
Keun-Ok Lee ◽  
Franziska Aemisegger ◽  
Stephan Pfahl ◽  
Cyrille Flamant ◽  
Jean-Lionel Lacour ◽  
...  
Keyword(s):  
Large Scale ◽  
Cold Front ◽  
Heavy Precipitation ◽  
Convective Precipitation ◽  
Water Isotopes ◽  
Precipitation Event ◽  
Stable Water Isotopes ◽  
Heavy Precipitation Event ◽  
The North ◽  
Upper Level

Abstract. The dynamical context and moisture transport pathways embedded in large-scale flow and associated with a heavy precipitation event (HPE) in southern Italy (SI) are investigated with the help of stable water isotopes (SWIs) based on a purely numerical framework. The event occurred during the Intensive Observation Period (IOP) 13 of the field campaign of the Hydrological Cycle in the Mediterranean Experiment (HyMeX) on 15 and 16 October 2012, and SI experienced intense rainfall of 62.4 mm over 27 h with two precipitation phases during this event. The first one (P1) was induced by convective precipitation ahead of a cold front, while the second one (P2) was mainly associated with precipitation induced by large-scale uplift. The moisture transport and processes responsible for the HPE are analysed using a simulation with the isotope-enabled regional numerical model COSMOiso. The simulation at a horizontal grid spacing of about 7 km over a large domain (about 4300 km ×3500 km) allows the isotopes signal to be distinguished due to local processes or large-scale advection. Backward trajectory analyses based on this simulation show that the air parcels arriving in SI during P1 originate from the North Atlantic and descend within an upper-level trough over the north-western Mediterranean. The descending air parcels reach elevations below 1 km over the sea and bring dry and isotopically depleted air (median δ18O ≤-25 ‰, water vapour mixing ratio q≤2 g kg−1) close to the surface, which induces strong surface evaporation. These air parcels are rapidly enriched in SWIs (δ18O ≥-14 ‰) and moistened (q≥8 g kg−1) over the Tyrrhenian Sea by taking up moisture from surface evaporation and potentially from evaporation of frontal precipitation. Thereafter, the SWI-enriched low-level air masses arriving upstream of SI are convectively pumped to higher altitudes, and the SWI-depleted moisture from higher levels is transported towards the surface within the downdrafts ahead of the cold front over SI, producing a large amount of convective precipitation in SI. Most of the moisture processes (i.e. evaporation, convective mixing) related to the HPE take place during the 18 h before P1 over SI. A period of 4 h later, during the second precipitation phase P2, the air parcels arriving over SI mainly originate from north Africa. The strong cyclonic flow around the eastward-moving upper-level trough induces the advection of a SWI-enriched African moisture plume towards SI and leads to large-scale uplift of the warm air mass along the cold front. This lifts moist and SWI-enriched air (median δ18O ≥-16 ‰, median q≥6 g kg−1) and leads to gradual rain out of the air parcels over Italy. Large-scale ascent in the warm sector ahead of the cold front takes place during the 72 h preceding P2 in SI. This work demonstrates how stable water isotopes can yield additional insights into the variety of thermodynamic mechanisms occurring at the mesoscale and synoptic scale during the formation of a HPE.

Do Statistical Pattern Corrections Improve Seasonal Climate Predictions in the North American Multimodel Ensemble Models?

2017 ◽  
Vol 30 (20) ◽  
pp. 8335-8355 ◽  
Author(s):  
Anthony G. Barnston ◽  
Michael K. Tippett
Keyword(s):  
North American ◽  
Large Scale ◽  
Climate Model ◽  
Principal Component ◽  
Eastern Africa ◽  
Multimodel Ensemble ◽  
Anomaly Correlation ◽  
The North ◽  
The Individual ◽  
North American Multimodel Ensemble

Abstract Canonical correlation analysis (CCA)-based statistical corrections are applied to seasonal mean precipitation and temperature hindcasts of the individual models from the North American Multimodel Ensemble project to correct biases in the positions and amplitudes of the predicted large-scale anomaly patterns. Corrections are applied in 15 individual regions and then merged into globally corrected forecasts. The CCA correction dramatically improves the RMS error skill score, demonstrating that model predictions contain correctable systematic biases in mean and amplitude. However, the corrections do not materially improve the anomaly correlation skills of the individual models for most regions, seasons, and lead times, with the exception of October–December precipitation in Indonesia and eastern Africa. Models with lower uncorrected correlation skill tend to benefit more from the correction, suggesting that their lower skills may be due to correctable systematic errors. Unexpectedly, corrections for the globe as a single region tend to improve the anomaly correlation at least as much as the merged corrections to the individual regions for temperature, and more so for precipitation, perhaps due to better noise filtering. The lack of overall improvement in correlation may imply relatively mild errors in large-scale anomaly patterns. Alternatively, there may be such errors, but the period of record is too short to identify them effectively but long enough to find local biases in mean and amplitude. Therefore, statistical correction methods treating individual locations (e.g., multiple regression or principal component regression) may be recommended for today’s coupled climate model forecasts. The findings highlight that the performance of statistical postprocessing can be grossly overestimated without thorough cross validation or evaluation on independent data.

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.

Sign in / Sign up

Export Citation Format

Share Document