scholarly journals A Synoptic Climatology of Northern Hemisphere, Cold Season Polar and Subtropical Jet Superposition Events

2017 ◽  
Vol 30 (18) ◽  
pp. 7231-7246 ◽  
Author(s):  
Croix E. Christenson ◽  
Jonathan E. Martin ◽  
Zachary J. Handlos
Keyword(s):  
Northern Hemisphere ◽  
Structural Characteristics ◽  
Cold Season ◽  
Hadley Cell ◽  
Synoptic Climatology ◽  
Jet Streams ◽  
Subtropical Jet ◽  
Wave Development ◽  
Different Origins ◽  
Subtropical Jets

Abstract Narrow, tropopause-level wind speed maxima known as jet streams or jets are among the most ubiquitous structural characteristics of Earth’s atmosphere. Two species, the polar and subtropical jets, can be observed on any given day. The polar jet is tied, via eddy momentum flux convergence associated with extratropical wave development, to the troposphere-deep baroclinicity of the midlatitudes, while the subtropical jet is tied, by angular momentum constraints, to the poleward edge of the tropical Hadley cell. As a consequence of their different origins, the polar and subtropical jets are separated by both latitude and elevation. However, there are times when these two usually separate features become vertically superposed to form a single, intense jet core designated as a jet superposition or superposed jet. An objective method for identifying tropopause-level jets is employed in the construction of 50-yr cold season (November–March) synoptic climatologies of the Northern Hemisphere polar jet, subtropical jet, and jet superpositions. The analysis demonstrates that while superposition events are relatively rare, there are clear geographical maxima. Superpositions are most frequent in the western Pacific from December through February, with a secondary peak in southern North America and along its eastern seaboard. Consistent with expectations, the spatiotemporal maxima in jet superpositions appear to be coincident with maxima in the polar and subtropical jets.

scholarly journals A study on the maintenance of the winter subtropical jet streams in the northern hemisphere

1988 ◽  
Vol 40 (5) ◽  
pp. 392-397
Author(s):  
Tsing-Chang Chen ◽  
Ren-Yow Tzeng ◽  
Harry Van Loon
Keyword(s):  
Northern Hemisphere ◽  
Jet Streams ◽  
Subtropical Jet

scholarly journals Measurements of the movement of the jet streams at mid-latitudes, in the Northern and Southern Hemispheres, 1979 to 2010

2011 ◽  
Vol 11 (11) ◽  
pp. 31067-31090 ◽  
Author(s):  
R. D. Hudson
Keyword(s):  
Greenhouse Gases ◽  
Radiative Forcing ◽  
Linear Regression Analysis ◽  
Volcanic Eruptions ◽  
Hadley Cell ◽  
Jet Streams ◽  
Quasi Biennial Oscillation ◽  
Subtropical Jet ◽  
Direct Radiative Forcing ◽  
Major Factors

Abstract. Previous studies have shown that the mean latitude of the subtropical jet streams in both hemispheres have shifted toward the poles over the last few decades. This paper presents a study of the movement of both the subtropical and Polar fronts, the location of the respective jet streams, between 1979 and 2010 at mid-latitudes, using total ozone measurements to identify the sharp horizontal boundary that occurs at the position of the fronts. Previous studies have shown that the two fronts are the boundaries of three distinct regimes in the stratosphere, corresponding to the Hadley. Ferrel, and Polar meridionally overturning circulation cells in the troposphere, each of which has a distinct temperature profile. Over the period of study the horizontal area of the Hadley cell has increased at latitudes between 20 and 60 degrees while the area of the Polar cell has decreased. A linear regression analysis was performed to identify the major factors associated with the movement of the subtropical jet streams. These were: (1) changes in the Tropical land/ocean temperature, (2) direct radiative forcing from greenhouse gases in the troposphere, (3) changes in the temperature of the lower Tropical stratosphere, (4) the Quasi-Biennial Oscillation, and (5) volcanic eruptions. The dominant mechanism was the direct radiative forcing from greenhouse gases. Over the period of study the poleward movement of the subtropical jet streams was 3.7±0.3 degrees in the Northern Hemisphere and 6.5±0.2 degrees in the Southern Hemisphere, with a net expansion of the Tropical belt of 10.2 degrees. Previous studies have shown that weather systems tend to follow the jet streams. The observed poleward movement in both hemispheres over the past thirty years represents a significant change in the position of the subtropical jet streams, which should lead to significant latitudinal shifts in the global weather patterns, temperatures, precipitation and the hydrologic cycle.

scholarly journals Measurements of the movement of the jet streams at mid-latitudes, in the Northern and Southern Hemispheres, 1979 to 2010

2012 ◽  
Vol 12 (16) ◽  
pp. 7797-7808 ◽  
Author(s):  
R. D. Hudson
Keyword(s):  
Greenhouse Gases ◽  
Radiative Forcing ◽  
Linear Regression Analysis ◽  
Volcanic Eruptions ◽  
Hadley Cell ◽  
Jet Streams ◽  
Quasi Biennial Oscillation ◽  
Subtropical Jet ◽  
Direct Radiative Forcing ◽  
Major Factors

Abstract. Previous studies have shown that the mean latitude of the sub-tropical jet streams in both hemispheres have shifted toward the poles over the last few decades. This paper presents a study of the movement of both the subtropical and Polar fronts, the location of the respective jet streams, between 1979 and 2010 at mid-latitudes, using total ozone measurements to identify the sharp horizontal boundary that occurs at the position of the fronts. Previous studies have shown that the two fronts are the boundaries of three distinct regimes in the stratosphere, corresponding to the Hadley, Ferrel, and polar meridionally overturning circulation cells in the troposphere. Over the period of study the horizontal area of the Hadley cell has increased at latitudes between 20 and 60 degrees while the area of the Polar cell has decreased. A linear regression analysis was performed to identify the major factors associated with the movement of the subtropical jet streams. These were: (1) changes in the Tropical land plus ocean temperature, (2) direct radiative forcing from greenhouse gases in the troposphere, (3) changes in the temperature of the lower tropical stratosphere, (4) the Quasi-Biennial Oscillation, and (5) volcanic eruptions. The dominant mechanism was the direct radiative forcing from greenhouse gases. Between 1979 and 2010 the poleward movement of the subtropical jet streams was 3.7 ± 0.3 degrees in the Northern Hemisphere and 6.5 ± 0.2 degrees in the Southern Hemisphere. Previous studies have shown that weather systems tend to follow the jet streams. The observed poleward movement in both hemispheres over the past thirty years represents a significant change in the position of the sub-tropical jet streams, which should lead to significant latitudinal shifts in the global weather patterns and the hydrologic cycle.

scholarly journals A network-based detection scheme for the jet stream core

2017 ◽  
Vol 8 (1) ◽  
pp. 75-89 ◽  
Author(s):  
Sonja Molnos ◽  
Tarek Mamdouh ◽  
Stefan Petri ◽  
Thomas Nocke ◽  
Tino Weinkauf ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Probability Distributions ◽  
Reanalysis Data ◽  
Western Hemisphere ◽  
Jet Stream ◽  
Jet Streams ◽  
Detection Scheme ◽  
The North ◽  
Eastern Hemisphere ◽  
Subtropical Jet

Abstract. The polar and subtropical jet streams are strong upper-level winds with a crucial influence on weather throughout the Northern Hemisphere midlatitudes. In particular, the polar jet is located between cold arctic air to the north and warmer subtropical air to the south. Strongly meandering states therefore often lead to extreme surface weather. Some algorithms exist which can detect the 2-D (latitude and longitude) jets' core around the hemisphere, but all of them use a minimal threshold to determine the subtropical and polar jet stream. This is particularly problematic for the polar jet stream, whose wind velocities can change rapidly from very weak to very high values and vice versa. We develop a network-based scheme using Dijkstra's shortest-path algorithm to detect the polar and subtropical jet stream core. This algorithm not only considers the commonly used wind strength for core detection but also takes wind direction and climatological latitudinal position into account. Furthermore, it distinguishes between polar and subtropical jet, and between separate and merged jet states. The parameter values of the detection scheme are optimized using simulated annealing and a skill function that accounts for the zonal-mean jet stream position (Rikus, 2015). After the successful optimization process, we apply our scheme to reanalysis data covering 1979–2015 and calculate seasonal-mean probabilistic maps and trends in wind strength and position of jet streams. We present longitudinally defined probability distributions of the positions for both jets for all on the Northern Hemisphere seasons. This shows that winter is characterized by two well-separated jets over Europe and Asia (ca. 20° W to 140° E). In contrast, summer normally has a single merged jet over the western hemisphere but can have both merged and separated jet states in the eastern hemisphere. With this algorithm it is possible to investigate the position of the jets' cores around the hemisphere and it is therefore very suitable to analyze jet stream patterns in observations and models, enabling more advanced model-validation.

A study on the maintenance of the winter subtropical jet streams in the northern hemisphere

1988 ◽  
Vol 40A (5) ◽  
pp. 392-397 ◽  
Author(s):  
TSING-CHANG CHEN ◽  
REN-YOW TZENG ◽  
HARRY LOON
Keyword(s):  
Northern Hemisphere ◽  
Jet Streams ◽  
Subtropical Jet

scholarly journals The sensitivity of the large-scale atmosphere circulation to changes in surface temperature gradients in the Northern Hemisphere

2017 ◽  
Author(s):  
Sonja Molnos ◽  
Stefan Petri ◽  
Jascha Lehmann ◽  
Erik Peukert ◽  
Dim Coumou
Keyword(s):  
Temperature Gradient ◽  
Surface Temperature ◽  
Northern Hemisphere ◽  
Large Scale ◽  
Planetary Waves ◽  
Hadley Cell ◽  
Temperature Fields ◽  
Storm Tracks ◽  
Meridional Temperature Gradient ◽  
Jet Streams

Abstract. Climate and weather conditions in the mid-latitudes are strongly driven by the large-scale atmosphere circulation. Observational data indicates that important components of the large-scale circulation have changed in recent decades including the strength of the Hadley cell, jet streams, storm tracks and planetary waves. Associated impacts cover a broad range, including changes in the frequency and nature of weather extremes and shifts of fertile habitats with implications for biodiversity and agriculture. Dynamical theories have been proposed that link the shift of the poleward edge of the Northern Hadley cell to changes in the meridional temperature gradient. Moreover, model simulations have been carried out to analyse the cause of observed and projected changes in the large-scale atmosphere circulation. However, the question of the underlying drivers and particularly the possible role of global warming is still debated. Here, we use a statistical-dynamical atmosphere model (SDAM) to analyse the sensitivity of the Northern Hemisphere Hadley cell, storm tracks, jet streams and planetary waves to changes in temperature fields by systematically altering the zonal and meridional temperature gradient as well as the global mean surface temperature.

scholarly journals Composite Analysis of Large-Scale Environments Conducive to Western Pacific Polar/Subtropical Jet Superposition

2016 ◽  
Vol 29 (19) ◽  
pp. 7145-7165 ◽  
Author(s):  
Zachary J. Handlos ◽  
Jonathan E. Martin
Keyword(s):  
Large Scale ◽  
Hadley Cell ◽  
Entrance Region ◽  
Western Pacific ◽  
Northwest Pacific ◽  
Jet Streams ◽  
Research Attention ◽  
Subtropical Jet ◽  
Cold Surges ◽  
The Western Pacific

Abstract Although considerable research attention has been devoted to examination of the Northern Hemisphere polar and subtropical jet streams, relatively little has been directed toward understanding the circumstances that conspire to produce the relatively rare vertical superposition of these usually separate features. This study investigates the structure and evolution of large-scale environments associated with jet superposition events in the northwest Pacific. An objective identification scheme, using NCEP–NCAR Reanalysis 1 data, is employed to identify all jet superpositions in the western Pacific (30°–40°N, 135°–175°E) for boreal winters (DJF) between 1979/80 and 2009/10. The analysis reveals that environments conducive to western Pacific jet superposition share several large-scale features usually associated with East Asian winter monsoon (EAWM) northerly cold surges, including the presence of an enhanced Hadley cell–like circulation within the jet entrance region. It is further demonstrated that several EAWM indices are statistically significantly correlated with jet superposition frequency in the western Pacific. The life cycle of EAWM cold surges promotes interaction between tropical convection and internal jet dynamics. Low–potential vorticity (PV), high- air, appearing to be associated with anomalous convection in the western Pacific lower latitudes, is advected poleward toward the equatorward side of the jet in upper-tropospheric isentropic layers, resulting in anomalous anticyclonic wind shear that accelerates the jet. This, along with geostrophic cold air advection in the left jet entrance region that drives the polar tropopause downward through the jet core, promotes the development of the deep, vertical PV wall characteristic of superposed jets. A conceptual model synthesizing the results of this analysis is introduced.

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