scholarly journals Systematic assessment of the diabatic processes that modify low-level potential vorticity in extratropical cyclones

2021 ◽  
Author(s):  
Roman Attinger ◽  
Elisa Spreitzer ◽  
Maxi Boettcher ◽  
Heini Wernli ◽  
Hanna Joos
Keyword(s):  
Temperature Difference ◽  
Cold Front ◽  
Warm Season ◽  
Cold Season ◽  
Radiative Heating ◽  
Extratropical Cyclones ◽  
Sea Temperature ◽  
Long Wave ◽  
Warm Front ◽  
Diabatic Processes

Abstract. Diabatic processes significantly affect the development and structure of extratropical cyclones. Previous studies quantified the dynamical relevance of selected diabatic processes by studying their influence on potential vorticity (PV) in individual cyclones. However, a more general assessment of the relevance of all PV-modifying processes in a larger ensemble of cyclones is currently missing. Based on a series of twelve 35-day model simulations using the Integrated Forecasting System (IFS) of the European Centre for Medium-range Weather Forecasts (ECMWF), this study systematically quantifies the relevance of individual diabatic processes for the dynamics of 288 rapidly intensifying extratropical cyclones. To this end, PV tendencies associated with each parametrized process in the model are accumulated along 15 h backward trajectories. The investigation focuses on regions of high PV (≥ 1 PVU) along the cold front, warm front, and in the cyclone center, as well as of negative PV (≤ −0.1 PVU) along the cold and warm front in the lower troposphere. On average, the primary processes that modify PV during the 24 h period of most rapid cyclone intensification remain temporally consistent for all anomalies considered. However, a pronounced case-to-case variability is found when comparing the dominant processes across individual cyclones. Along the cold front, PV is primarily generated by condensation in half of the investigated cyclones. For the remaining cyclones, convection or long-wave radiative cooling become the dominant process depending on environmental conditions. Results are similar for both seasons, with a reduced role of convection for the generation of PV along the cold front in the warm season. Negative PV west of the cold front is produced by turbulent exchange of momentum and temperature as well as long-wave radiative heating. The relevance of long-wave radiative heating is reduced during summer. The positive PV anomaly at the warm front is predominantly generated by condensation in the cold season, whereas turbulent mixing becomes the prevalent process during the warm season. Convection only plays a minor role for the generation of PV at the warm front. Negative PV along the warm front is produced by long-wave radiative heating, turbulent temperature tendencies, or melting of snow in the cold season. Turbulent temperature tendencies become the dominant process decreasing PV at the warm front in the warm season, together with melting of snow and turbulent exchange of momentum. The positive PV anomaly in the cyclone center is primarily produced by condensation, with only few cyclones where PV production is mainly associated with turbulent mixing or convection. A composite analysis further reveals that PV anomalies generated by convection require a negative air-sea temperature difference in the warm sector of the cyclone, which promotes a heat flux directed into the atmosphere and destabilizes the boundary layer. These cyclones primarily occur over warm ocean currents in the cold season. On the other hand, cyclones that occur in a significantly colder environment are often associated with a positive air-sea temperature difference in the warm sector, leading to PV generation by long-wave radiative cooling. Finally, long-wave radiative heating due to a negative air-sea temperature difference in the cold sector can produce negative PV along the cold and warm front. The general agreement between accumulated PV tendencies and the net PV change along trajectories is good. Therefore, the approach used in this study yields valuable insight regarding the specific physical processes that modify low-level PV in rapidly deepening extratropical cyclones.

scholarly journals Systematic assessment of the diabatic processes that modify low-level potential vorticity in extratropical cyclones

2021 ◽  
Vol 2 (4) ◽  
pp. 1073-1091
Author(s):  
Roman Attinger ◽  
Elisa Spreitzer ◽  
Maxi Boettcher ◽  
Heini Wernli ◽  
Hanna Joos
Keyword(s):  
Surface Temperature ◽  
Temperature Difference ◽  
Turbulent Mixing ◽  
Warm Season ◽  
Cold Season ◽  
Radiative Heating ◽  
Long Wave ◽  
Warm Front ◽  
Diabatic Processes ◽  
Pv Generation

Abstract. Diabatic processes significantly affect the development and structure of extratropical cyclones. Previous studies quantified the dynamical relevance of selected diabatic processes by studying their influence on potential vorticity (PV) in individual cyclones. However, a more general assessment of the relevance of all PV-modifying processes in a larger ensemble of cyclones is currently missing. Based on a series of twelve 35 d model simulations using the Integrated Forecasting System of the European Centre for Medium-Range Weather Forecasts, this study systematically quantifies the diabatic modification of positive and negative low-level PV anomalies along the cold front, warm front, and in the center of 288 rapidly intensifying extratropical cyclones. Diabatic PV modification is assessed by accumulating PV tendencies associated with each parametrized process along 15 h backward trajectories. The primary processes that modify PV typically remain temporally consistent during cyclone intensification. However, a pronounced case-to-case variability is found when comparing the most important processes across individual cyclones. Along the cold front, PV is primarily generated by condensation in half of the investigated cyclones in the cold season (October to March). For most of the remaining cyclones, convection or long-wave radiative cooling is the most important process. Similar results are found in the warm season (April to September); however, the fraction of cyclones with PV generation by convection as the most important process is reduced. Negative PV west of the cold front is primarily produced by turbulent mixing of momentum, long-wave radiative heating, or turbulent mixing of temperature. The positive PV anomaly at the warm front is most often primarily generated by condensation in the cold season and by turbulent mixing of momentum in the warm season. Convection is the most important process only in a few cyclones. Negative PV along the warm front is primarily produced by long-wave radiative heating, turbulent mixing of temperature, or melting of snow in the cold season. Turbulent mixing of temperature becomes the primary process in the warm season, followed by melting of snow and turbulent mixing of momentum. The positive PV anomaly in the cyclone center is primarily produced by condensation in most cyclones, with only few cases primarily associated with turbulent mixing or convection. A composite analysis further reveals that cyclones primarily associated with PV generation by convection exhibit a negative air–surface temperature difference in the warm sector, which promotes a heat flux directed into the atmosphere. These cyclones generally occur over warm ocean currents in the cold season. On the other hand, cyclones that occur in a significantly colder environment are often associated with a positive air–surface temperature difference in the warm sector, leading to PV generation by long-wave radiative cooling. Finally, long-wave radiative heating due to a negative air–surface temperature difference in the cold sector produces negative PV along the cold and warm front, in particular in the cold season.

5. Weather systems

2017 ◽  
Author(s):  
Storm Dunlop
Keyword(s):  
High Pressure ◽  
Cold Front ◽  
Low Pressure ◽  
Extratropical Cyclones ◽  
British Isles ◽  
Polar Lows ◽  
Atmospheric Rivers ◽  
Warm Sector ◽  
Warm Front ◽  
Low Pressure Systems

At temperate latitudes, such as those of the British Isles, the most significant changes in the weather, with major changes in wind strength and direction, as well as rainfall, are associated with the passage of depressions (low-pressure systems), more formally known as extratropical cyclones. ‘Weather systems’ describes the development of depressions, the different features within them (the warm front, the warm sector, the cold front, and the occluded front), and the likely weather produced. It also looks at isolated fronts, the sudden deepening of depressions, thermal and polar lows, atmospheric rivers, and the much quieter weather of high-pressure systems.

scholarly journals Characteristics of extratropical cyclones and precursors to windstorms in Northern Europe

2021 ◽  
Author(s):  
Terhi K. Laurila ◽  
Hilppa Gregow ◽  
Joona Cornér ◽  
Victoria A. Sinclair
Keyword(s):  
Potential Temperature ◽  
Storm Track ◽  
Warm Season ◽  
Cold Season ◽  
Northern Europe ◽  
Annual Number ◽  
Extratropical Cyclones ◽  
Maximum Wind ◽  
The North ◽  
Wind Gusts

Abstract. Extratropical cyclones play a major role in the atmospheric circulation, weather variability and can cause damage to society. Extratropical cyclones in Northern Europe, which is located at the end of the North Atlantic storm track, have been less studied than extratropical cyclones elsewhere. Our study investigates extratropical cyclones and windstorms in Northern Europe (which in this study covers Norway, Sweden, Finland, Estonia and parts of the Baltic, Norwegian and Barents Seas) by analysing their characteristics, spatial and temporal evolution and precursors. We examine cold and warm seasons separately to determine seasonal differences. We track all extratropical cyclones in Northern Europe, create cyclone composites and use an ensemble sensitivity method to analyse the precursors. The ensemble sensitivity analysis is a novel method in cyclone studies where linear regression is used to statistically identify what variables possibly influence the subsequent evolution of extratropical cyclones. We investigate windstorm precursors for both the minimum mean sea level pressure (MSLP) and for the maximum 10-m wind gusts. The annual number of extratropical cyclones and windstorms have a large inter-annual variability and no significant linear trends during 1980–2019. Windstorms originate and occur over the Barents and Norwegian Seas whereas weaker extratropical cyclones originate and occur over land areas in Northern Europe. During the windstorm evolution, the maximum wind gusts move from the warm sector to behind the cold front following the strongest pressure gradient. Windstorms in both seasons are located on the poleward side of the jet stream. The maximum wind gusts occur nearly at the same time than the minimum MSLP occurs. The cold season windstorms have higher sensitivities and thus are potentially better predictable than warm season windstorms, and the minimum MSLP has higher sensitivities than the maximum wind gusts. Of the four examined precursors, both the minimum MSLP and the maximum wind gusts are the most sensitive to the 850-hPa potential temperature anomaly i.e. the temperature gradient. Hence, this parameter is likely important when predicting windstorms in Northern Europe.

scholarly journals Characteristics of extratropical cyclones and precursors to windstorms in northern Europe

2021 ◽  
Vol 2 (4) ◽  
pp. 1111-1130
Author(s):  
Terhi K. Laurila ◽  
Hilppa Gregow ◽  
Joona Cornér ◽  
Victoria A. Sinclair
Keyword(s):  
Potential Temperature ◽  
Storm Track ◽  
Warm Season ◽  
Cold Season ◽  
Northern Europe ◽  
Annual Number ◽  
Extratropical Cyclones ◽  
Maximum Wind ◽  
The North ◽  
Wind Gusts

Abstract. Extratropical cyclones play a major role in the atmospheric circulation and weather variability and can cause widespread damage and destruction. Extratropical cyclones in northern Europe, which is located at the end of the North Atlantic storm track, have been less studied than extratropical cyclones elsewhere. Our study investigates extratropical cyclones and windstorms in northern Europe (which in this study covers Norway; Sweden; Finland; Estonia; and parts of the Baltic, Norwegian, and Barents seas) by analysing their characteristics, spatial and temporal evolution, and precursors. We examine cold and warm seasons separately to determine seasonal differences. We track all extratropical cyclones in northern Europe, create cyclone composites, and use an ensemble sensitivity method to analyse the precursors. The ensemble sensitivity analysis is a novel method in cyclone studies where linear regression is used to statistically identify what variables possibly influence the subsequent evolution of extratropical cyclones. We investigate windstorm precursors for both the minimum mean sea level pressure (MSLP) and for the maximum 10 m wind gusts. The annual number of extratropical cyclones and windstorms has a large inter-annual variability and no significant linear trends during 1980–2019. Windstorms originate and occur over the Barents and Norwegian seas, whereas weaker extratropical cyclones originate and occur over land areas in northern Europe. During the windstorm evolution, the maximum wind gusts move from the warm sector to behind the cold front following the strongest pressure gradient. Windstorms in both seasons are located on the poleward side of the jet stream. The maximum wind gusts occur nearly at the same time as the minimum MSLP occurs. The cold-season windstorms have higher sensitivities and thus are potentially better predictable than warm-season windstorms, and the minimum MSLP has higher sensitivities than the maximum wind gusts. Of the four examined precursors, both the minimum MSLP and the maximum wind gusts are the most sensitive to the 850 hPa potential temperature anomaly, i.e. the temperature gradient. Hence, this parameter is likely important when predicting windstorms in northern Europe.

scholarly journals Occluded Fronts and the Occlusion Process: A Fresh Look at Conventional Wisdom

2011 ◽  
Vol 92 (4) ◽  
pp. 443-466 ◽  
Author(s):  
David M. Schultz ◽  
Geraint Vaughan
Keyword(s):  
Frontal Zone ◽  
Cold Front ◽  
Heavy Precipitation ◽  
Conventional Wisdom ◽  
The Other ◽  
Extratropical Cyclones ◽  
New Paradigm ◽  
Warm Front ◽  
Catch Up ◽  
By Catch

Traditionally, the formation of an occluded front during the occlusion process in extratropical cyclones has been viewed as the catch-up of a faster-moving cold front to a slower-moving warm front separating the warm-sector air from the low center, as first described in the Norwegian cyclone model over 90 yr ago. In this article, the conventional wisdom, or the commonly held beliefs originating from the Norwegian cyclone model, about occluded fronts and the occlusion process are critically examined. The following four tenets of this conventional wisdom are addressed. First, the occlusion process is better described not by catch-up, but by the wrapping up and lengthening of the warm-air tongue as a result of deformation and rotation around the low center. Second, the merger of the cold front and warm front does not result in the frontal zone with the warmer air ascending over the other frontal zone. Instead, the occluded frontal zone tilts over the more statically stable frontal zone. Because a warmfrontal zone tends to be more stable than a cold-frontal zone, this process usually produces a warm-type occlusion, confirming that cold-type occlusions are less common than warm-type occlusions. Third, occlusion does not mean that the cyclone has stopped deepening, because many cyclones continue to deepen 10–30 mb for 12–36 h after the formation of the occluded front. Fourth, clouds and precipitation associated with occluded fronts differ from their widespread stratiform depiction in textbooks. Embedded precipitation bands may be parallel to the front, and little relationship may exist between the fronts and the cloud mass. These four tenets help to explain anomalies in the Norwegian cyclone model, such as how occluded fronts that spiral around the low center do not require catch-up to form, how Shapiro–Keyser cyclones undergo occlusion, why some cyclones do not form occluded fronts, how some cyclones deepen after occlusion, why few cold-type occlusions have been observed, and why occluded cyclones are often associated with heavy precipitation. This reexamination of conventional wisdom leads to a new paradigm for occluded fronts and occluded cyclones. A supplement to this article is available online: DOI: 10.1175/2010BAMS3057.2

scholarly journals Temperature and Relative Humidity Profile Retrieval from Fengyun-3D/HIRAS in the Arctic Region

2021 ◽  
Vol 13 (10) ◽  
pp. 1884
Author(s):  
Jingjing Hu ◽  
Yansong Bao ◽  
Jian Liu ◽  
Hui Liu ◽  
George P. Petropoulos ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Real Time ◽  
Wide Spectrum ◽  
Warm Season ◽  
Arctic Region ◽  
Cold Season ◽  
The Arctic ◽  
Practical Applications ◽  
A New Technique ◽  
The Arctic Region

The acquisition of real-time temperature and relative humidity (RH) profiles in the Arctic is of great significance for the study of the Arctic’s climate and Arctic scientific research. However, the operational algorithm of Fengyun-3D only takes into account areas within 60°N, the innovation of this work is that a new technique based on Neural Network (NN) algorithm was proposed, which can retrieve these parameters in real time from the Fengyun-3D Hyperspectral Infrared Radiation Atmospheric Sounding (HIRAS) observations in the Arctic region. Considering the difficulty of obtaining a large amount of actual observation (such as radiosonde) in the Arctic region, collocated ERA5 data from European Centre for Medium-Range Weather Forecasts (ECMWF) and HIRAS observations were used to train the neural networks (NNs). Brightness temperature and training targets were classified using two variables: season (warm season and cold season) and surface type (ocean and land). NNs-based retrievals were compared with ERA5 data and radiosonde observations (RAOBs) independent of the NN training sets. Results showed that (1) the NNs retrievals accuracy is generally higher on warm season and ocean; (2) the root-mean-square error (RMSE) of retrieved profiles is generally slightly higher in the RAOB comparisons than in the ERA5 comparisons, but the variation trend of errors with height is consistent; (3) the retrieved profiles by the NN method are closer to ERA5, comparing with the AIRS products. All the results demonstrated the potential value in time and space of NN algorithm in retrieving temperature and relative humidity profiles of the Arctic region from HIRAS observations under clear-sky conditions. As such, the proposed NN algorithm provides a valuable pathway for retrieving reliably temperature and RH profiles from HIRAS observations in the Arctic region, providing information of practical value in a wide spectrum of practical applications and research investigations alike.All in all, our work has important implications in broadening Fengyun-3D’s operational implementation range from within 60°N to the Arctic region.

scholarly journals Late Dorset architecture on Little Cornwallis Island, Nunavut

2005 ◽  
Vol 27 (1-2) ◽  
pp. 255-280 ◽  
Author(s):  
Genevieve LeMoine ◽  
James Helmer ◽  
Bjarne Grønnow
Keyword(s):  
Warm Season ◽  
Cold Season ◽  
Nuclear Families ◽  
Construction Techniques ◽  
Architectural Features ◽  
Size Number ◽  
Cornwallis Island

Abstract Late Dorset dwellings from two sites on Little Cornwallis Island (Nunavut) illustrate the diversity of architectural forms from this period. Ten architectural features are described. They include five tent rings, ascribed to warm season occupations, and five rectangular semi-subterranean houses with axial features, including one exceptionally well-preserved example, ascribed to cold season occupations. Variations in size, number of hearths, and construction techniques are examined and the use of both types of structures to house multiple nuclear families is suggested.

scholarly journals Protozooplankton characterization of two contrasting sites in a tropical coastal ecosystem (Guanabara Bay, RJ)

2007 ◽  
Vol 55 (1) ◽  
pp. 29-38 ◽  
Author(s):  
Eli Ana Traversim Gomes ◽  
Viviane Severiano dos Santos ◽  
Denise Rivera Tenenbaum ◽  
Maria Célia Villac
Keyword(s):  
Water Quality ◽  
Surface Water ◽  
Food Web ◽  
Warm Season ◽  
Descriptive Study ◽  
Cold Season ◽  
Guanabara Bay ◽  
Trophic Conditions ◽  
Plankton Dynamics

Much time and resources have been invested in understanding plankton dynamics in Guanabara Bay (Brazil), but no attention has been devoted to the protozooplankton. To fulfill this lacuna, abundance and composition of protozooplankton were investigated from January to December - 2000 in fortnightly surface water samplings at two distinct water quality sites (Urca - closer to the bay entrance, more saline and cleaner waters; Ramos - inner reaches, hypereutrophic waters). The density at Urca (10³ - 10(5) cell.l-1) was one to three orders of magnitude lower than at Ramos (10(4) - 10(5) cell.l-1). A seasonal trend for nanoplankton and protozooplankton was more evident at Urca, but both sites had lower densities during the colder period. Small heterotrophic dinoflagellates (20-30 mm) were dominant in over 50% of the samples. The protozooplankton abundance and composition reflected the distinct trophic conditions states found at the bay. During the wet-warm season, non-oligotrich ciliates were representative of Ramos site with Gymnodiniaceae dinoflagellates, while tintinnids and heterotrophic dinoflagellates were predominantly found at Urca mainly during the dry-cold season. This first descriptive study towards the understanding of the intricate relationships among the microbial food web components reveals that protozooplankton can be a good indicator of water quality conditions at the bay.

scholarly journals Diet composition and feeding habits of the eyespot skate, Atlantoraja cyclophora (Elasmobranchii: Arhynchobatidae), off Uruguay and northern Argentina

2016 ◽  
Vol 14 (3) ◽  
Author(s):  
Santiago A. Barbini ◽  
Luis O. Lucifora
Keyword(s):  
Body Size ◽  
Diet Composition ◽  
Prey Size ◽  
Prey Availability ◽  
Feeding Habits ◽  
Warm Season ◽  
Cold Season ◽  
The North ◽  
Multiple Hypothesis ◽  
Modelling Approach

ABSTRACT The eyespot skate, Atlantoraja cyclophora, is an endemic species from the southwestern Atlantic, occurring from Rio de Janeiro, Brazil, to northern Patagonia, Argentina. The feeding habits of this species, from off Uruguay and north Argentina, were evaluated using a multiple hypothesis modelling approach. In general, the diet was composed mainly of decapod crustaceans, followed by teleost fishes. Molluscs, mysidaceans, amphipods, isopods, lancelets and elasmobranchs were consumed in lower proportion. The consumption of shrimps drecreased with increasing body size of A. cyclophora. On the other hand, the consumption of teleosts increased with body size. Mature individuals preyed more heavily on crabs than immature individuals. Teleosts were consumed more in the south region (34º - 38ºS) and crabs in the north region (38º - 41ºS). Shrimps were eaten more in the warm season than in the cold season. Prey size increased with increasing body size of A. cyclophora , but large individuals also consumed small teleosts and crabs. Atlantoraja cyclophora has demersal-benthic feeding habits, shifts its diet with increasing body size and in response to seasonal and regional changes in prey availability and distribution.

scholarly journals Annual cycles of organochlorine pesticide enantiomers in Arctic air suggest changing sources and pathways

2015 ◽  
Vol 15 (3) ◽  
pp. 1411-1420 ◽  
Author(s):  
T. F. Bidleman ◽  
L. M. Jantunen ◽  
H. Hung ◽  
J. Ma ◽  
G. A. Stern ◽  
...  
Keyword(s):  
Warm Season ◽  
Open Water ◽  
Cold Season ◽  
Secondary Emission ◽  
Air Monitoring ◽  
The Arctic ◽  
Gas Chromatography Mass Spectrometry ◽  
Annual Cycles ◽  
Digital Filtration ◽  
Peak Areas

Abstract. Air samples collected during 1994–2000 at the Canadian Arctic air monitoring station Alert (82°30' N, 62°20' W) were analysed by enantiospecific gas chromatography–mass spectrometry for α-hexachlorocyclohexane (α-HCH), trans-chlordane (TC) and cis-chlordane (CC). Results were expressed as enantiomer fractions (EF = peak areas of (+)/[(+) + (−)] enantiomers), where EFs = 0.5, < 0.5 and > 0.5 indicate racemic composition, and preferential depletion of (+) and (−) enantiomers, respectively. Long-term average EFs were close to racemic values for α -HCH (0.504 ± 0.004, n = 197) and CC (0.505 ± 0.004, n = 162), and deviated farther from racemic for TC (0.470 ± 0.013, n = 165). Digital filtration analysis revealed annual cycles of lower α-HCH EFs in summer–fall and higher EFs in winter–spring. These cycles suggest volatilization of partially degraded α-HCH with EF < 0.5 from open water and advection to Alert during the warm season, and background transport of α-HCH with EF > 0.5 during the cold season. The contribution of sea-volatilized α-HCH was only 11% at Alert, vs. 32% at Resolute Bay (74.68° N, 94.90° W) in 1999. EFs of TC also followed annual cycles of lower and higher values in the warm and cold seasons. These were in phase with low and high cycles of the TC/CC ratio (expressed as FTC = TC/(TC+CC)), which suggests greater contribution of microbially "weathered" TC in summer–fall versus winter–spring. CC was closer to racemic than TC and displayed seasonal cycles only in 1997–1998. EF profiles are likely to change with rising contribution of secondary emission sources, weathering of residues in the environment, and loss of ice cover in the Arctic. Enantiomer-specific analysis could provide added forensic capability to air monitoring programs.

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