Role of the Low-Frequency Deformation Field on the Explosive Growth of Extratropical Cyclones at the Jet Exit. Part I: Barotropic Critical Region

2006 ◽  
Vol 63 (8) ◽  
pp. 1965-1981 ◽  
Author(s):  
G. Rivière ◽  
A. Joly
Keyword(s):  
Critical Region ◽  
Large Scale ◽  
Sudden Change ◽  
Storm Track ◽  
Low Frequency ◽  
Reanalysis Data ◽  
Deformation Field ◽  
Extratropical Cyclones ◽  
Exit Region

Abstract By using new theoretical results on perturbation growth in spatially and temporally complex quasigeostrophic flows, this paper investigates the role of the large-scale deformation field on extratropical cyclones and especially on their explosive growth in the jet-exit region. Theoretical ideas are tested by decomposing the atmospheric flow into a high- and a low-frequency part and by analyzing four-dimensional variational data assimilation (4DVAR) reanalysis data of the Fronts and Atlantic Storm-Track Experiment (FASTEX) during February 1997 as well as reanalysis data for the end of December 1999. Regions where the low-frequency deformation magnitude is greater than the absolute value of the low-frequency vorticity are shown to correspond to regions where synoptic disturbances at the same level tend to be located. These regions in the upper troposphere are intrinsically related to the horizontal inhomogeneities of the low-frequency large-scale upper-tropospheric jet but cannot be detected by looking separately at the deformation or vorticity. Transitions from one such large-scale region to the next furthermore can be accompanied by a sudden change of the dilatation axes orientation: this combination defines a barotropic critical region (BtCR). Reasons why a BtCR is a specific place where barotropic development is likely to occur are exposed. Two very differently located BtCR regions in two apparently similar zonal-like weather regimes are shown to be the preferred regions where synoptic eddies tend to cross the jet from the south to the north. BtCRs are also special regions where constructive association between barotropic and baroclinic processes is favored, indeed constrained to cooperate. This is illustrated through the detailed analysis of the last growth stage of Intensive Observation Period 17 (IOP17) of FASTEX. It happens precisely around a BtCR area located in the jet-exit region. Two processes explain this IOP17 development; one involves the barotropic generation rate resulting from the low crossing the BtCR and the other one is baroclinic interaction, which is strongly maintained far away from the baroclinicity maximum because of the new favorable baroclinic configuration resulting from the first process.

Drivers of biases in the extratropical storm tracks in CMIP6

2020 ◽  
Author(s):  
Matthew Priestley ◽  
Duncan Ackerley ◽  
Jennifer Catto ◽  
Kevin Hodges ◽  
Ruth McDonald ◽  
...  
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Storm Track ◽  
Storm Tracks ◽  
Extratropical Cyclones ◽  
Ocean Coupling ◽  
Coupled Climate Models ◽  
The Mean ◽  
The Impact

<p>Extratropical cyclones are the leading driver of the day-to-day weather variability and wintertime losses for Europe. In the latest generation of coupled climate models, CMIP6, it is hoped that with improved modelling capabilities come improvements in the structure of the storm track and the associated cyclones. Using an objective cyclone identification and tracking algorithm the mean state of the storm tracks in the CMIP6 models is assessed as well as the representation of explosively deepening cyclones. Any developments and improvements since the previous generation of models in CMIP5 are discussed, with focus on the impact of model resolution on storm track representation. Furthermore, large-scale drivers of any biases are investigated, with particular focus on the role of atmosphere-ocean coupling via associated AMIP simulations and also the influence of large-scale dynamical and thermodynamical features.</p>

scholarly journals Role of the Low-Frequency Deformation Field on the Explosive Growth of Extratropical Cyclones at the Jet Exit. Part II: Baroclinic Critical Region

2006 ◽  
Vol 63 (8) ◽  
pp. 1982-1995 ◽  
Author(s):  
G. Rivière ◽  
A. Joly
Keyword(s):  
Critical Region ◽  
High Frequency ◽  
Large Scale ◽  
Intermediate Phase ◽  
Low Frequency ◽  
Atmospheric Flow ◽  
Upper Level ◽  
Large Scale Flow ◽  
Upper Level Jet

Abstract Midlatitude cyclones tend to develop strongly in specific locations relative to the large-scale flow, such as jet-exit zones. Here, the approach developed in Part I that highlights the role of large-scale deformation in constraining the location of such events is continued. The atmospheric flow is decomposed into a high- and low-frequency part separating large and synoptic scales. A new low-frequency diagnostic has been introduced, called effective deformation Δm. It is defined as σ2m − ζ2m, where σm is the low-frequency deformation magnitude and ζm is the low-frequency vorticity. While Part I focused on large-scale conditions inducing an intermediate phase of barotropic growth, the present paper concentrates on other configurations that rather prevent this phase from happening. This large-scale circulation is characterized by the presence of a strong zonal upper-level jet and a lower-level jet that are meridionally quite far from each other over the Atlantic but close to one another in the eastern Atlantic region. As high-frequency disturbances are trapped by the effective deformation of the low-frequency jets, the increasing closeness of the two jets associated with that of the two effective deformation fields computed in the lower and upper levels defines a region called the baroclinic critical region where upper high-frequency disturbances and surface cyclones may strongly interact baroclinically. The increased baroclinic energy collection resulting from this constrained configuration change is outlined. An analysis of the explosive growth of the Christmas wind storms of 1999 and of mid-December 2004 provides different realizations of this configuration and associated mechanism.

Depth-integrated equation for hydro-acoustic waves with bottom damping

2015 ◽  
Vol 766 ◽  
Author(s):  
Ali Abdolali ◽  
James T. Kirby ◽  
Giorgio Bellotti
Keyword(s):  
Acoustic Waves ◽  
Large Scale ◽  
Model Equation ◽  
Low Frequency ◽  
3D Models ◽  
Sediment Layer ◽  
Sea Bed ◽  
Weakly Compressible ◽  
Acoustic Wave Generation

AbstractWe present a depth-integrated equation for the mechanics of generation, propagation and dissipation of low-frequency hydro-acoustic waves due to sudden bottom displacement in a weakly compressible ocean overlying a weakly compressible viscous sediment layer. The model is validated against a full 3D computational model. Physical properties of these waves are studied and compared with those for waves over a rigid sea bed, revealing changes in the frequency spectrum and modal peaks. The resulting model equation can be used for numerical prediction in large-scale domains, overcoming the computational difficulties of 3D models while taking into account the role of bottom dissipation on hydro-acoustic wave generation and propagation.

scholarly journals Contribution of low-frequency climatic–oceanic oscillations to streamflow variability in small, coastal rivers of the Sierra Nevada de Santa Marta (Colombia)

2019 ◽  
Vol 23 (5) ◽  
pp. 2379-2400 ◽  
Author(s):  
Juan Camilo Restrepo ◽  
Aldemar Higgins ◽  
Jaime Escobar ◽  
Silvio Ospino ◽  
Natalia Hoyos
Keyword(s):  
Energy Spectrum ◽  
Sierra Nevada ◽  
Large Scale ◽  
Low Frequency ◽  
Maximum Power ◽  
Simultaneous Occurrence ◽  
Atmospheric Processes ◽  
Low Frequency Oscillations ◽  
Streamflow Variability

Abstract. This study evaluated the influence of low-frequency oscillations, that are linked to large-scale oceanographic–atmospheric processes, on streamflow variability in small tropical coastal mountain rivers of the Sierra Nevada de Santa Marta, Colombia. We used data from six rivers that had > 32 years of complete, continuous monthly streamflow records. This investigation employed spectral analyses to (1) explore temporal characteristics of streamflow variability, (2) estimate the net contribution to the energy spectrum of low-frequency oscillations to streamflow anomalies, and (3) analyze the linkages between streamflow anomalies and large-scale, low-frequency oceanographic–atmospheric processes. Wavelet analyses indicate that the 8–12-year component exhibited a quasi-stationary state, with a peak of maximum power between 1985 and 2005. These oscillations were nearly in phase in all rivers. Maximum power peaks occurred for the Palomino and Rancheria rivers in 1985 and 1995, respectively. The wavelet spectrum highlights a change in river variability patterns between 1995 and 2015, characterized by a shift towards the low-frequency oscillations' domain (8–12 years). The net contribution of these oscillations to the energy spectrum was as high as 51 %, a value much larger than previously thought for rivers in northwestern South America. The simultaneous occurrence of hydrologic oscillations, as well as the increase in the amplitude of the 8–12-year band, defined periods of extremely anomalous wet seasons during 1989–1990, 1998–2002 and 2010–2011, reflecting the role of low-frequency oscillations in modulating streamflow variability in these rivers. Cross-wavelet transform and wavelet coherence revealed high common powers and significant coherences in low-frequency bands (>96 months) between streamflow anomalies and Atlantic Meridional Oscillation (AMO), Pacific Decadal Oscillation (PDO) and the Tropical North Atlantic Index (TNA). These results show the role of large-scale, low-frequency oceanographic–climate processes in modulating the long-term hydrological variability of these rivers.

scholarly journals Atmospheric Forcing of Debris Flows in the Southern Swiss Alps

2013 ◽  
Vol 52 (7) ◽  
pp. 1554-1560 ◽  
Author(s):  
Andrea Toreti ◽  
Michelle Schneuwly-Bollschweiler ◽  
Markus Stoffel ◽  
Jürg Luterbacher
Keyword(s):  
Time Series ◽  
Debris Flow ◽  
Debris Flows ◽  
Large Scale ◽  
Reanalysis Data ◽  
Swiss Alps ◽  
Classification Algorithms ◽  
Precipitation Series ◽  
Large Scale Circulation

AbstractThis article addresses the role of large-scale circulation and thermodynamical features in the release of past debris flows in the Swiss Alps by using classification algorithms, potential instability, and convective time scale. The study is based on a uniquely dense dendrogeomorphic time series of debris flows covering the period 1872–2008, reanalysis data, instrumental time series, and gridded hourly precipitation series (1992–2006) over the area. Results highlight the crucial role of synoptic and mesoscale forcing as well as of convective equilibrium on triggering rainfalls. Two midtropospheric synoptic patterns favor anomalous southwesterly flow toward the area and high potential instability. These findings imply a certain degree of predictability of debris-flow events and can therefore be used to improve existing alert systems.

scholarly journals The Role of Extratropical Cyclones and Fronts for Southern Ocean Freshwater Fluxes

2014 ◽  
Vol 27 (16) ◽  
pp. 6205-6224 ◽  
Author(s):  
Lukas Papritz ◽  
Stephan Pfahl ◽  
Irina Rudeva ◽  
Ian Simmonds ◽  
Harald Sodemann ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Interannual Variability ◽  
High Latitude ◽  
Storm Track ◽  
Extratropical Cyclones ◽  
Freshwater Flux ◽  
Freshwater Fluxes ◽  
South Indian ◽  
The Pacific

Abstract In this study, the important role of extratropical cyclones and fronts for the atmospheric freshwater flux over the Southern Ocean is analyzed. Based on the Interim ECMWF Re-Analysis (ERA-Interim), the freshwater flux associated with cyclones is quantified and it is revealed that the structure of the Southern Hemispheric storm track is strongly imprinted on the climatological freshwater flux. In particular, during austral winter the spiraliform shape of the storm track leads to a band of negative freshwater flux bending toward and around Antarctica, complemented by a strong freshwater input into the midlatitude Pacific, associated with the split storm track. The interannual variability of the wintertime high-latitude freshwater flux is shown to be largely determined by the variability of strong precipitation (>75th percentile). Using a novel and comprehensive method to attribute strong precipitation uniquely to cyclones and fronts, it is demonstrated that over the Southern Ocean between 60% and 90% of the strong precipitation events are due to these synoptic systems. Cyclones are the dominant cause of strong precipitation around Antarctica and in the midlatitudes of the Atlantic and the Pacific, while in the south Indian Ocean and the eastern Atlantic fronts bring most of the strong precipitation. A detailed analysis of the spatial variations of intense front and cyclone precipitation associated with the interannual variability of the wintertime frequency of cyclones in the midlatitude and high-latitude branches of the Pacific storm track underpins the importance of considering both fronts and cyclones in the analysis of the interannual variability of freshwater fluxes.

scholarly journals North Atlantic midwinter storm track suppression and the European weather response in ERA5 reanalysis

2021 ◽  
Author(s):  
Estefania Montoya Duque ◽  
Frank Lunkeit ◽  
Richard Blender
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Storm Track ◽  
Reanalysis Data ◽  
Band Pass Filter ◽  
Pass Filter ◽  
The North ◽  
Temperature And Precipitation ◽  
Precipitation Increase ◽  
Precipitation Anomalies

AbstractIn this study, we analyse the influence of North Atlantic midwinter storm track suppressions on European synoptic temperature and precipitation anomalies to determine the large-scale conditions relevant for the so-called Christmas thaw. We diagnose this relation in daily ERA5 reanalysis data in the spatial resolution of 0.25∘ between 1979 and 2018. To access synoptic time scales, a 3–10-day band-pass filter is applied. An index for the suppression is defined by the upper tropospheric Eddy Kinetic Energy (EKE) anomalies in the North Atlantic. We define the strong jet stream years as the year exceeding the 75% of the winter seasonal values at 250 hPa. In winters with strong jet activity, the storm track suppression is found, in agreement with the barotropic governor mechanism. Composites of European surface temperature and precipitation for low index values reveal weakly warmer conditions during winter (DJF) in Central Europe and the British Isles and a distinct cooling in Northern Europe. In the 1-month interval during December 15 to January 15, the warming is more pronounced. The clearest signal is the precipitation increase with a magnitude of 1 mm/day in the Mediterranean region.

scholarly journals The role of North Atlantic-European weather regimes in the surface impact of sudden stratospheric warming events

2020 ◽  
Author(s):  
Daniela I. V. Domeisen ◽  
Christian M. Grams ◽  
Lukas Papritz
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Western Europe ◽  
Storm Track ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Weather Regimes ◽  
The North ◽  
The North Atlantic

Abstract. Sudden stratospheric warming (SSW) events can significantly impact tropospheric weather for a period of several weeks, in particular over the North Atlantic and Europe. However, not all SSW events exhibit the same tropospheric response, if any, and it remains an open question what determines the existence, location, timing, and strength of the downward impact. We here explore the role of the state of the tropospheric flow in the North Atlantic region at the onset of SSW events for determining the subsequent surface impact. A refined definition of seven North Atlantic tropospheric weather regimes indicates the Greenland blocking (GL) and Atlantic Trough (AT) regimes as the most frequent large-scale patterns following the weeks after an SSW. While GL is dominated by high pressure over Greenland, AT is dominated by a southeastward shifted storm track in the North Atlantic. We find that a blocking situation over western Europe and the North Sea (European Blocking) at the time of the SSW onset favours the GL response and the associated cold conditions over Europe. In contrast, an AT response and mild conditions are more likely if GL occurs already at SSW onset. For the remaining tropospheric flow regimes during SSW onset, we find no clear response. The results indicate that the tropospheric impact of SSW events critically depends on the tropospheric state during the onset of the SSW, which could provide crucial guidance for subseasonal prediction.

scholarly journals Svalbard’s Mesoscale Environmental Factor Impact on the Wind Field

Atmosphere ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1165
Author(s):  
Małgorzata Kitowska ◽  
Tomasz Petelski
Keyword(s):  
Large Scale ◽  
Sea Breeze ◽  
Reanalysis Data ◽  
Atmospheric Measurements ◽  
Atmospheric Circulation Patterns ◽  
Wind Speeds ◽  
Circulation Types ◽  
Circulation Patterns ◽  
The Difference

The mesoscale circulation along the west shore of Spitsbergen is largely controlled by the difference in temperature between the glaciers and surface sea temperatures. We describe how the mesoscale effect influences the atmospheric circulation patterns. The conducted research was based on reanalysis data, model data, and atmospheric measurements; wind data from different sources and scales were compared and analysed. We discuss the situations wherein the mesoscale effect can be identified by analysing the wind direction or its velocity. This study shows the role of the mesoscale effect on the wind in the Svalbard region. Different situations according to the atmospheric patterns taken from a catalogue of 21 circulation types for each day created for Svalbard are analysed and compared with cases of land-sea breeze type circulation for the 20-year period between 1994 and 2013. It is proved that even if it is not possible to distinguish this mesoscale effect based on the difference between local and large-scale wind directions, this factor can be observed by studying the wind speeds. It is claimed that as long as there are glaciers on Spitsbergen, there will be a mesoscale land-sea breeze type circulation controlled by the difference in air temperature over land and water.

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