scholarly journals Searching for the Elusive Cold-Type Occluded Front

2014 ◽  
Vol 142 (8) ◽  
pp. 2565-2570 ◽  
Author(s):  
David M. Schultz ◽  
Bogdan Antonescu ◽  
Alessandro Chiariello
Keyword(s):  
Temperature Difference ◽  
Cross Sections ◽  
Frontal Zone ◽  
North Atlantic Ocean ◽  
Air Mass ◽  
Cold Air ◽  
Weather Forecasts ◽  
The North ◽  
Medium Range ◽  
Frontal Zones

Abstract According to the Norwegian cyclone model, whether a warm-type or cold-type occluded front forms depends upon which cold air mass is colder: the prewarm-frontal air mass or the postcold-frontal air mass. For example, a cold-type occlusion is said to occur when the occluded front slopes rearward with height because the prewarm-frontal air mass is warmer than the postcold-frontal air mass. This temperature difference and the resulting occluded-frontal structure in the Norwegian cyclone model is part of what is called the temperature rule. Paradoxically, no clear example of a rearward-sloping, cold-type occluded front has been found in the literature, even though the required temperature difference has been documented in several cases. This article presents the first documented, rearward-sloping, cold-type occluded front. This occluded front forms in a cyclone over the North Atlantic Ocean on 3–5 January 2003 and is documented in model output from the European Centre for Medium-Range Weather Forecasts. Cross sections through the evolving cyclone show the occluded front forms as the less statically stable warm-frontal zone ascends over the more stable cold-frontal zone. Such a stability difference between the cold- and warm-frontal zones is consistent with a previously published hypothesis that the less stable air is lifted by the more stable air to form occluded fronts, in disagreement with the temperature rule. Because warm-frontal zones and the cold air underneath tend to be more stable than cold-frontal zones and the postcold-frontal air, warm-type occluded fronts are much more common than cold-type occluded fronts, explaining why well-defined, rearward-sloping, cold-type occluded fronts are not common in the meteorological literature.

Investigation of the Capacity Factor of Weather-Routed Energy Ships Deployed in the Near-Shore

2021 ◽  
Author(s):  
Roshamida Abd Jamil ◽  
Jean-Christophe Gilloteaux ◽  
Philippe Lelong ◽  
Aurélien Babarit
Keyword(s):  
Wind Power ◽  
North Atlantic Ocean ◽  
Capacity Factor ◽  
Offshore Wind ◽  
Power Performance ◽  
Weather Forecasts ◽  
The North ◽  
Weather Routing ◽  
Near Shore ◽  
Water Turbines

Abstract The energy ship concept has been proposed as an alternative wind power conversion system to harvest offshore wind energy. Energy ships are ships propelled by the wind and which generate electricity by means of water turbines attached underneath their hull, The generated electricity is stored on-board (batteries, hydrogen, etc.) It has been shown that energy ships deployed far-offshore in the North Atlantic Ocean may achieve capacity factors over 80% using weather-routing. The present paper complements this research by investigating the capacity factors of energy ships harvesting wind power in the near-shore. Two case studies are considered: the French islands of Saint-Pierre et-Miquelon, near Canada, and Ile de Sein, near metropolitan France. The methodology is as follows. First, the design of the energy ship considered in this study is presented. It was developed using an in-house Velocity, and Power Performance Program (VPPP) developed at LHEEA. The velocity and power production polar plots of the ship were used as input to a modified version of the weather-routing software QtVlm. This software was then used for capacity factor optimization using 10m altitude wind data analysis which was extracted from the ERA-Interim dataset provided by the European Centre for Medium-Range Weather Forecasts (ECMWF). Three years (2015, 2016, and 2017) data are considered. The results show that average capacity factors of approximately 40% and 40% can be achieved at Ile de Sein and Saint-Pierre-et-Miquelon with considered energy ship design.

scholarly journals Isentropic Analysis of Polar Cold Airmass Streams in the Northern Hemispheric Winter

2014 ◽  
Vol 71 (6) ◽  
pp. 2230-2243 ◽  
Author(s):  
Toshiki Iwasaki ◽  
Takamichi Shoji ◽  
Yuki Kanno ◽  
Masahiro Sawada ◽  
Masashi Ujiie ◽  
...  
Keyword(s):  
North Atlantic Ocean ◽  
North Pacific Ocean ◽  
Potential Temperature ◽  
Heat Content ◽  
The Arctic ◽  
Eastern Coast ◽  
Mean Flow ◽  
Air Mass ◽  
Cold Air ◽  
Northern Hemispheric

Abstract An analysis method is proposed for polar cold airmass streams from generation to disappearance. It designates a threshold potential temperature θT at around the turning point of the extratropical direct (ETD) meridional circulation from downward to equatorward in the mass-weighted isentropic zonal mean (MIM) and clarifies the geographical distributions of the cold air mass, the negative heat content (NHC), their horizontal fluxes, and their diabatic change rates on the basis of conservation relations of the air mass and thermodynamic energy. In the Northern Hemispheric winter, the polar cold air mass below θT = 280 K has two main streams: the East Asian stream and the North American stream. The former grows over the northern part of the Eurasian continent, flows eastward, turns down southeastward toward East Asia via Siberia, and disappears over the western North Pacific Ocean. The latter grows over the Arctic Ocean, flows toward the eastern coast of North America via Hudson Bay, and disappears over the western North Atlantic Ocean. In their exit regions, wave–mean flow interactions are considered to transfer the angular momentum from the cold airstreams to the upward Eliassen–Palm flux and convert the available potential energy to wave energy.

scholarly journals A Multifaceted Climatology of Atmospheric Blocking and Its Recent Linear Trend

2007 ◽  
Vol 20 (4) ◽  
pp. 633-649 ◽  
Author(s):  
M. Croci-Maspoli ◽  
C. Schwierz ◽  
H. C. Davies
Keyword(s):  
North Pacific ◽  
Linear Trend ◽  
Age Distribution ◽  
Atmospheric Blocking ◽  
Weather Forecasts ◽  
The North ◽  
Four Seasons ◽  
Medium Range ◽  
The Mean ◽  
The North Pacific

Abstract A dynamically based climatology is derived for Northern Hemisphere atmospheric blocking events. Blocks are viewed as large amplitude, long-lasting, and negative potential vorticity (PV) anomalies located beneath the dynamical tropopause. The derived climatology [based on the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40)] provides a concise, coherent, and illuminating description of the main physical characteristics of blocks and the accompanying linear trends. The latitude–longitude distribution of blocking frequency captures the standard bimodal geographical distribution with major peaks over the North Atlantic and eastern North Pacific in all four seasons. The accompanying pattern for the age distribution, the genesis–lysis regions, and the track of blocks reveals that 1) younger blocks (1–4 days) are more prevalent at lower latitudes whereas significantly older blocks (up to 12 days) are located at higher latitudes; 2) genesis is confined predominantly to the two major ocean basins and in a zonal band between 40° and 50°N latitude, whereas lysis is more dispersed but with clear preference to higher latitudes; and 3) the general northeastward–west-northwest movement of blocks in the genesis–lysis phase also exhibits subtle seasonal and intra- and interbasin differences. Examination of the intensity and spatial-scale changes during the blocking life cycle suggests that in the mean a block’s evolution is independent of the genesis region and its eventual duration. A novel analysis of blocking trends reveals significant negative trends in winter over Greenland and in spring over the North Pacific. It is shown that the changes over Greenland are linked to the number of blocking episodes, whereas a neighboring trend signal to the south is linked to higher-frequency anticyclonic systems. Furthermore, evidence is adduced that changes in blocking frequency contribute seminally to tropopause height trends.

Potential Temperature and Potential Vorticity Inversion: Complementary Approaches

2010 ◽  
Vol 67 (12) ◽  
pp. 4001-4016 ◽  
Author(s):  
Joseph Egger ◽  
Klaus-Peter Hoinka
Keyword(s):  
North Atlantic ◽  
Potential Vorticity ◽  
Potential Temperature ◽  
Storm Track ◽  
Temperature Inversion ◽  
Weather Forecasts ◽  
The North ◽  
Potential Vorticity Inversion ◽  
Medium Range ◽  
Balanced Flow

Abstract Given the distribution of one atmospheric variable, that of nearly all others can be derived in balanced flow. In particular, potential vorticity inversion (PVI) selects potential vorticity (PV) to derive pressure, winds, and potential temperature θ. Potential temperature inversion (PTI) starts from available θ fields to derive pressure, winds, and PV. While PVI has been applied extensively, PTI has hardly been used as a research tool although the related technical steps are well known and simpler than those needed in PVI. Two idealized examples of PTI and PVI are compared. The 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) datasets are used to determine typical anomalies of PV and θ in the North Atlantic storm-track region. Statistical forms of PVI and PTI are applied to these anomalies. The inversions are equivalent but the results of PTI are generally easier to understand than those of PVI. The issues of attribution and piecewise inversion are discussed.

scholarly journals Subseasonal Variations of Wintertime North Pacific Evaporation, Cold Air Surges, and Water Vapor Transport

2017 ◽  
Vol 30 (23) ◽  
pp. 9475-9491 ◽  
Author(s):  
Xuejuan Ren ◽  
Xiu-Qun Yang ◽  
Haibo Hu
Keyword(s):  
Water Vapor ◽  
North Pacific ◽  
Wave Train ◽  
Vapor Transport ◽  
Specific Humidity ◽  
Water Vapor Transport ◽  
Vapor Source ◽  
Air Mass ◽  
Cold Air ◽  
The North

This study addresses subseasonal variations of oceanic evaporation E over the North Pacific during winter and the connection with the cold air surges (CASs) and atmospheric water vapor transport using the OAFlux and ERA-Interim daily data. By performing an empirical orthogonal function (EOF) analysis, two dominant modes of subseasonal evaporation anomaly E′ are identified: a zonal wave train–like pattern (EOF1) and an east negative–west positive dipolar pattern (EOF2) in the midlatitude basin. Further analyses yield the following conclusions. 1) The Siberian high (SH)-related CAS has a crucial role in generation of the EOF1 mode of E′. When the dry and cold air mass passes the region of the warm Kuroshio and its extension [Kuroshio–Oyashio Extension (KOE)], the increased air–sea temperature and moisture differences and intensified wind speed lead to the above-normal oceanic E, and vice versa. 2) The Aleutian low (AL)-related CAS contributes to the EOF2 mode of E′. The intensified AL transports a dramatically colder and drier air mass toward the KOE region and a slightly warmer and wetter one toward the west coast of North America, leading to the east negative–west positive structure of E′ in the midlatitude basin. 3) A quasi-linear relationship exists between E′ and divergent water vapor transport anomalies over the KOE region. Positive (negative) E′ is generally accompanied by anomalous vapor source (sink). 4) The divergent water vapor transport anomalies associated with the two EOFs are preliminarily decided by their individual lower-level wind field anomalies and second by the meridional inhomogeneity of subseasonal specific humidity anomalies. Hydroclimate effects on precipitation over the pan–North Pacific region are also discussed.

Aerosol black carbon and radon as tracers for air mass origin over the North Atlantic Ocean

1990 ◽  
Vol 4 (2) ◽  
pp. 189-199 ◽  
Author(s):  
A. D. A. Hansen ◽  
R. S. Artz ◽  
A. A. P. Pszenny ◽  
R. E. Larson
Keyword(s):  
Atlantic Ocean ◽  
Black Carbon ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Air Mass ◽  
The North ◽  
The North Atlantic ◽  
Air Mass Origin

scholarly journals An Examination of Tropical Cyclone Position, Intensity, and Intensity Life Cycle within Atmospheric Reanalysis Datasets

2012 ◽  
Vol 25 (10) ◽  
pp. 3453-3475 ◽  
Author(s):  
Benjamin A. Schenkel ◽  
Robert E. Hart
Keyword(s):  
Life Cycle ◽  
North Pacific ◽  
Strongly Correlated ◽  
Sea Level Pressure ◽  
Climate Forecast System Reanalysis ◽  
Weather Forecasts ◽  
The North ◽  
Medium Range ◽  
The Mean ◽  
Modern Era

Abstract The following study examines the position and intensity differences of tropical cyclones (TCs) among the Best-Track and five atmospheric reanalysis datasets to evaluate the degree to which reanalyses are appropriate for studying TCs. While significant differences are found in both reanalysis TC intensity and position, the representation of TC intensity within reanalyses is found to be most problematic owing to its underestimation beyond what can be attributed solely to the coarse grid resolution. Moreover, the mean life cycle of normalized TC intensity within reanalyses reveals an underestimation of both prepeak intensification rates as well as a delay in peak intensity relative to the Best-Track. These discrepancies between Best-Track and reanalysis TC intensity and position can further be described through correlations with such parameters as Best-Track TC age, Best-Track TC intensity, Best-Track TC location, and the extended Best-Track TC size. Specifically, TC position differences within the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40), ECMWF Interim Re-Analysis (ERA-I), and Modern Era Retrospective-Analysis for Research and Applications (MERRA) exhibit statistically significant correlations (0.27 ≤ R ≤ 0.38) with the proximity of TCs to observation dense areas in the North Atlantic (NATL) and western North Pacific (WPAC). Reanalysis TC intensity is found to be most strongly correlated with Best-Track TC size (0.53 ≤ R ≤ 0.70 for maximum 10-m wind speed; −0.71 ≤ R ≤ −0.53 for minimum mean sea level pressure) while exhibiting smaller, yet significant, correlations with Best-Track TC age, Best-Track TC intensity, and Best-Track TC latitude. Of the three basins examined, the eastern North Pacific (EPAC) has the largest reanalysis TC position differences and weakest intensities possibly due to a relative dearth of observations, the strong nearby terrain gradient, and the movement of TCs away from the most observation dense portion of the basin over time. The smaller mean Best-Track size and shorter mean lifespan of Best-Track EPAC TCs may also yield weaker reanalysis TC intensities. Of the five reanalyses, the smaller position differences and stronger intensities found in the Climate Forecast System Reanalysis (CFSR) and Japanese 25-year Reanalysis (JRA-25) are attributed to the use of vortex relocation and TC wind profile retrievals, respectively. The discrepancies in TC position between the Best-Track and reanalyses combined with the muted magnitude of TC intensity and its partially nonphysical life cycle within reanalyses suggests that caution should be exercised when utilizing these datasets for studies that rely either on TC intensity (raw or normalized) or track. Finally, several cases of nonphysical TC structure also argue that further work is needed to improve TC representation while implying that studies focusing solely on TC intensity and track do not necessarily extend to other aspects of TC representation.

scholarly journals The Impact of Analysis Error on Medium-Range Weather Forecasts

2008 ◽  
Vol 136 (9) ◽  
pp. 3425-3431 ◽  
Author(s):  
Kyle L. Swanson ◽  
Paul J. Roebber
Keyword(s):  
North Pacific Ocean ◽  
Forecast Skill ◽  
Ensemble Spread ◽  
Weather Forecasts ◽  
The North ◽  
Medium Range ◽  
Difference Fields ◽  
Height Fields ◽  
Analysis Error ◽  
The Impact

Abstract All meteorological analyzed fields contain errors, the magnitude of which ultimately determines the point at which a given forecast will fail. Here, the authors explore the extent to which analysis difference fields capture certain aspects of the actual but unknowable flow-dependent analysis error. The analysis difference fields considered here are obtained by subtracting the NCEP and ECMWF reanalysis 500-hPa height fields. It is shown that the magnitude of this 500-hPa analysis difference averaged over the North Pacific Ocean has a statistically significant impact on forecast skill over the continental United States well into the medium range (5 days). Further, it is shown that the impact of this analysis difference on forecast skill is similar to that of ensemble spread well into the medium range, a measure of forecast uncertainty currently used in the operational setting. Finally, the analysis difference and ensemble spread are shown to be independent; hence, the impact of these two quantities upon forecast skill is additive.

Effects of Different Configurations of the East Asian Subtropical and Polar Front Jets on Precipitation during the Mei-Yu Season

2014 ◽  
Vol 27 (17) ◽  
pp. 6660-6672 ◽  
Author(s):  
Li Li ◽  
Yaocun Zhang
Keyword(s):  
East Asian ◽  
Polar Front ◽  
Moist Air ◽  
Air Mass ◽  
Cold Air ◽  
Air Masses ◽  
The North ◽  
Huai River ◽  
Intensity Changes ◽  
East Asian Jet Stream

Abstract Observational analysis indicates that the East Asian jet stream consists of two separate branches: the East Asian subtropical jet (EASJ) and the East Asian polar front jet (EAPJ). The impacts of different intensity configurations of the EASJ and EAPJ on precipitation during the mei-yu season are investigated using the NCEP–NCAR Reanalysis Project (NNRP) dataset and daily gauge observations in East China. The intensity and location of precipitation are associated with different configurations of the EASJ and EAPJ. Precipitation intensity increases with intensification of the EASJ and EAPJ. The rainband is located to the north of the mei-yu region when the EASJ intensifies and the EAPJ weakens. Further analyses indicate that the intensity changes of the EASJ and EAPJ are linked to the cold and warm airmass activities. For cases with strong EASJ and EAPJ, both the warm-moist and cold air masses are active. When the warm-moist and cold air masses meet near 30°N, abundant precipitation occurs in the Yangtze-Huai River basin (YHRB). For cases with weak EASJ and EAPJ, both the cold and warm-moist air masses are inactive, and no significant precipitation occurs in the YHRB. For cases with strong EASJ and weak EAPJ, the warm-moist air mass moves northward while the cold air mass is weak. Precipitation concentrates to the north of YHRB. For cases with weak EASJ and strong EAPJ, cold air extends farther south while the warm-moist air mass is inactive. Precipitation occurs to the south of YHRB.

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