Distribution of Jet Streams in the North Atlantic, Europe and the Mediterranean, 1957–8

1961 ◽  
Vol 14 (4) ◽  
pp. 432-445
Author(s):  
A. F. Crossley
Keyword(s):  
North Atlantic ◽  
Critical Speed ◽  
Jet Stream ◽  
Jet Streams ◽  
Once Daily ◽  
Upper Troposphere ◽  
The North ◽  
Four Seasons ◽  
The North Atlantic ◽  
The Mediterranean

From an inspection of upper-air contour charts for 300 and 200 mb., the location of the axis of jet streams of 80 kt. or more has been assessed once daily over the two years 1957–8. Results are presented for each of the four seasons by means of isopleths of frequency (Fig. 1) and also by means of frequency-roses in areas of 5 degrees of latitude by 10 degrees of longitude (Figs. 2–5); each rose shows the number of occasions of direction of the axis from the eight compass points. The area covered extends from latitude 30° N. to 70° N., and from longitude 60° W. to 30° E. An Appendix contains some discussion of the technique of locating the axis of jet streams on contour charts.The characteristics of jet streams were described in a paper by Chambers in this Journal for July/October 1959. The present paper goes a stage further by giving the number of occurrences of jet streams per season over a two-year period in an area from the North Atlantic to the Mediterranean. The number of occurrences depends very much on the chosen definition, about which there is no general agreement. Whilst a jet stream may be fairly described as a fast-moving stream of air in the upper troposphere with great extension in the direction of the wind and persistence of the order of days, for statistical purposes it is necessary to be more precise. In this paper a critical speed of 80 kt. is required at the 300- or 200-mb. level in order that the stream shall qualify as a jet stream. Further discussion of this point is given in the Appendix, but any definition is largely subjective and it does not matter a great deal what definition is used provided the reader is aware of the limits to which the statistics refer.

Distribution of Jet Streams at 200 mb. in the Middle East

1967 ◽  
Vol 20 (4) ◽  
pp. 397-404
Author(s):  
A. F. Crossley ◽  
I. N. Parkinson
Keyword(s):  
Middle East ◽  
North Atlantic ◽  
Eastern Mediterranean ◽  
Jet Streams ◽  
North West ◽  
The North ◽  
European Area ◽  
The North Atlantic ◽  
The Mediterranean ◽  
The Persian Gulf

1. INTRODUCTION. The distribution of jet streams over the North Atlantic, Europe and the Mediterranean for the two years 1957–8 was described in an earlier paper (Crossley, 1961); the present paper extends the study to the area which is here referred to somewhat loosely as the Middle East —it extends between latitudes 40° N. and 10;° N., and from longitude 30° E. to 90° E. in the north but to only 65° E. in the south (Fig. 1). The aircraft trunk routes intersecting this area include those from the Eastern Mediterranean across Arabia and the Persian Gulf to West Pakistan and north-west India.The jet streams which affect the Atlantic-European area in the upper troposphere are mostly of the ‘polar’ type with a core in the neighbourhood of 300 mb. so that they can be conveniently located as a rule on the contour charts for 300 mb.; in the Mediterranean region and in the corresponding latitudes of the North Atlantic the westerly subtropical jet stream is also concerned and charts for both 300 and 200 mb.

scholarly journals A seesaw in Mediterranean precipitation during the Roman Period linked to millennial-scale changes in the North Atlantic

2012 ◽  
Vol 8 (2) ◽  
pp. 637-651 ◽  
Author(s):  
B. J. Dermody ◽  
H. J. de Boer ◽  
M. F. P. Bierkens ◽  
S. L. Weber ◽  
M. J. Wassen ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North Atlantic ◽  
Roman Period ◽  
Sea Surface ◽  
Jet Stream ◽  
The North ◽  
The North Atlantic ◽  
The Mediterranean ◽  
Millennial Scale

Abstract. We present a reconstruction of the change in climatic humidity around the Mediterranean between 3000–1000 yr BP. Using a range of proxy archives and model simulations we demonstrate that climate during this period was typified by a millennial-scale seesaw in climatic humidity between Spain and Israel on one side and the Central Mediterranean and Turkey on the other, similar to precipitation anomalies associated with the East Atlantic/West Russia pattern in current climate. We find that changes in the position and intensity of the jet stream indicated by our analysis correlate with millennial changes in North Atlantic sea surface temperature. A model simulation indicates the proxies of climatic humidity used in our analysis were unlikely to be influenced by climatic aridification caused by deforestation during the Roman Period. That finding is supported by an analysis of the distribution of archaeological sites in the Eastern Mediterranean which exhibits no evidence that human habitation distribution changed since ancient times as a result of climatic aridification. Therefore we conclude that changes in climatic humidity over the Mediterranean during the Roman Period were primarily caused by a modification of the jet stream linked to sea surface temperature change in the North Atlantic. Based on our findings, we propose that ocean-atmosphere coupling may have contributed to regulating Atlantic Meridional Overturning Circulation intensity during the period of analysis.

Which regional cloud-radiative changes are most important for the global warming response of the midlatitude jet streams?

2020 ◽  
Author(s):  
Nicole Albern ◽  
Aiko Voigt ◽  
David W. J. Thompson ◽  
Joaquim G. Pinto
Keyword(s):  
Global Warming ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
North Atlantic ◽  
Radiative Heating ◽  
Jet Stream ◽  
Jet Streams ◽  
The North ◽  
The North Atlantic ◽  
The Impact

<p>Clouds and the midlatitude circulation are strongly coupled via radiation. Previous studies showed that global cloud-radiative changes contribute significantly to the global warming response of the midlatitude circulation. Here, we investigate the impact of regional cloud-radiative changes and identify which regional cloud-radiative changes are most important for the impact of global cloud-radiative changes. We show how tropical, midlatitude and polar cloud-radiative changes modify the annual-mean, wintertime and summertime jet stream response to global warming across ocean basins. To this end, we perform global simulations with the atmospheric component of the ICOsahedral Nonhydrostatic (ICON) model. We prescribe sea surface temperatures (SST) to isolate the impact of cloud-radiative changes via the atmospheric pathway, i.e. changes in atmospheric cloud-radiative heating, and mimic global warming by a uniform 4K SST increase. We apply the cloud-locking method to break the cloud-radiation-circulation coupling and to decompose the circulation response into contributions from cloud-radiative changes and from the SST increase.</p><p>In response to global warming, the North Atlantic, North Pacific, Northern Hemisphere and Southern Hemisphere jet streams shift poleward and the North Atlantic, Northern Hemisphere and Southern Hemisphere jets strengthen. Global cloud-radiative changes contribute to these jet responses in all ocean basins. <span>In the annual-mean and DJF, tropical and midlatitude cloud-radiative changes contribute significantly to the poleward jet shift in all ocean basins. </span><span>P</span><span>olar cloud-radiative changes shift the jet streams </span><span>poleward </span><span>in the northern hemispheric ocean basins </span><span>but</span> <span>equatorward </span><span>in the Southern Hemisphere. In JJA, the poleward jet shift is small in all ocean basins. In contrast to the jet shift, the global cloud-radiative impacts on the 850hPa zonal wind and jet strength responses </span><span>result predominantly from </span><span>tropical cloud-radiative </span><span>changes</span><span>.</span></p><p><span>The cloud-radiative impact on the jet shift can be related to changes in upper-tropospheric baroclinicity via increases in upper-tropospheric meridional temperature gradients, enhanced wave activity and increased eddy momentum fluxes. However, the response of the atmospheric temperature to cloud-radiative heating is </span><span>more difficult to understand because it is modulated by other small-scale processes such as convection and the circulation.</span><span> Our results help to understand the jet stream response to global warming and highlight the importance of regional cloud-radiative changes for this response, </span><span>in particular those in the tropics</span><span>.</span></p>

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>

North Atlantic Oscillation-related impacts on precipitation over the Italian Peninsula during the 1979-2020 period

2021 ◽  
Author(s):  
Paula Lorenzo Sánchez ◽  
Leonardo Aragão
Keyword(s):  
High Resolution ◽  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Mediterranean Region ◽  
Italian Peninsula ◽  
The North ◽  
Nao Index ◽  
The North Atlantic ◽  
The Mediterranean ◽  
Resolution Dataset

<p>The North Atlantic Oscillation (NAO) has been widely recognized as one of the main patterns of atmospheric variability over the northern hemisphere, helping to understand variations on the North Atlantic Jet (NAJ) position and its influence on storm-tracks, atmospheric blocking and Rossby Wave breaking. Among several relevant teleconnection patterns identified through different timescales, the most prominent ones are found for northern Europe during winter months, when positive (negative) phases of NAO are related to wetter (drier) conditions. Although it is not well defined yet, an opposite connection is observed for the Mediterranean region, where negative NAO values are often associated with high precipitation. Therefore, the main goal of this study is to identify which regions and periods of the year are the most susceptible to abundant NAO-related precipitation throughout the Italian Peninsula. For doing so, the last 42 years period (1979-2020) was analysed using the Fifth Generation ECMWF Atmospheric ReAnalysis of the Global Climate (ERA5). The NAO index was calculated using the Mean Sea Level Pressure (MSLP) extracted from the nearest gridpoints to Reykjavik, Ponta Delgada, Lisbon and Gibraltar, with a time resolution of one hour and horizontal spatial resolution of 0.25ºx0.25º. Both NAO index and MSLP time series were validated for different timescales (hourly, daily, monthly and seasonal) using the Automated Surface Observing System data and the Climatic Research Unit (CRU) high-resolution dataset (based on measured data). High correlations, ranging from 0.92 to 0.98, were found for all stations, timescales and evaluated parameters. To quantify the influence of NAO over the Mediterranean region, the monthly averaged ERA5 ‘total precipitation’ data over the Italian Peninsula [35-48º N; 5-20º E] were used. As expected, the results concerning NAO x Precipitation presented the best correlations when analysed monthly, confirming some of the already known NAO signatures over the Italian Peninsula: higher correlations during winter and over the Tyrrhenian coast, and lower correlations during summer and over the Apennines, the Adriatic Sea and the Ionian Sea. On the other hand, the precipitation over the Alps and the Tunisian coast presented a remarkable signature of positive NAO values that, despite a lower statistical significance (85-90%), is in agreement with recent findings of observational studies. In addition, significant negative correlations were identified for the spring and autumn months over the Tyrrhenian area. Among those, the high correlations found during May are particularly interesting, as they follow the behaviour described in recent studies performed using the same high-resolution dataset (ERA5), which have identified an increased number of cyclones over the Mediterranean during this month. This connection suggests that NAO could also be used to explore the potential penetration of the North Atlantic depressions into the Mediterranean Basin. </p><p>Keywords: NAO; Teleconnections; ERA5; ReAnalysis; Mediterranean; Climatology.</p>

Impact of Seasonality in the North Atlantic Jet Stream and Storm Migration on the Seasonality of Hurricane Translation Speed Changes

2021 ◽  
pp. 1-38
Author(s):  
Xi Guo ◽  
James P. Kossin ◽  
Zhe-Min Tan
Keyword(s):  
North Atlantic ◽  
Atlantic Coast ◽  
Jet Stream ◽  
Translation Speed ◽  
Multidecadal Variability ◽  
The Past ◽  
The North ◽  
Term Variation ◽  
The North Atlantic

AbstractTropical cyclone (TC) translation speed (TCTS) can affect the duration of TC-related disasters, which is critical to coastal and inland areas. The long-term variation of TCTS and their relationship to the variability of the mid-latitude jet stream and storm migration are discussed here for storms near the North Atlantic coast during 1948-2019. Our results reveal the prominent seasonality in the long-term variation of TCTS, which can be largely explained by the seasonality in the covariations of the mid-latitude jet stream and storm locations. Specifically, significant increases of TCTS occur in June and October during the past decades, which may result from the equatorward displacement of the jet stream and poleward migration of storm locations. Prominent slowdown of TCTS is found in August, which is related to the weakened jet strength and equatorward storm migration. In September, the effects of poleward displacement and weakening of the jet stream on TCTS are largely compensated by the poleward storm migration, therefore, no significant change in TCTS is observed. Meanwhile, the multidecadal variability of the Atlantic may contribute to the multidecadal variability of TCTS. Our findings emphasize the significance in taking a seasonality view in discussing the variability and trends of near-coast Atlantic TCTS under climate change.

A Role for Barotropic Eddy–Mean Flow Feedbacks in the Zonal Wind Response to Sea Ice Loss and Arctic Amplification

2019 ◽  
Vol 32 (21) ◽  
pp. 7469-7481 ◽  
Author(s):  
Bryn Ronalds ◽  
Elizabeth A. Barnes
Keyword(s):  
Sea Ice ◽  
North Atlantic ◽  
Zonal Wind ◽  
Jet Stream ◽  
Arctic Amplification ◽  
Mean Flow ◽  
Jet Streams ◽  
The North ◽  
Wind Response ◽  
The North Pacific

Abstract Previous studies have suggested that, in the zonal mean, the climatological Northern Hemisphere wintertime eddy-driven jet streams will weaken and shift equatorward in response to Arctic amplification and sea ice loss. However, multiple studies have also pointed out that this response has strong regional differences across the two ocean basins, with the North Atlantic jet stream generally weakening across models and the North Pacific jet stream showing signs of strengthening. Based on the zonal wind response with a fully coupled model, this work sets up two case studies using a barotropic model to test a dynamical mechanism that can explain the differences in zonal wind response in the North Pacific versus the North Atlantic. Results indicate that the differences between the two basins are due, at least in part, to differences in the proximity of the jet streams to the sea ice loss, and that in both cases the eddies act to increase the jet speed via changes in wave breaking location and frequency. Thus, while baroclinic arguments may account for an initial reduction in the midlatitude winds through thermal wind balance, eddy–mean flow feedbacks are likely instrumental in determining the final total response and actually act to strengthen the eddy-driven jet stream.

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