Dynamical coupling of the stratosphere and mesosphere in the 2002 Southern Hemisphere major stratospheric sudden warming

2005 ◽  
Vol 32 (13) ◽  
Author(s):  
H.-L. Liu
Keyword(s):  
Southern Hemisphere ◽  
Stratospheric Sudden Warming ◽  
Dynamical Coupling

scholarly journals Stratosphere–Troposphere Coupling in a Relatively Simple AGCM: The Importance of Stratospheric Variability

2009 ◽  
Vol 22 (8) ◽  
pp. 1920-1933 ◽  
Author(s):  
Edwin P. Gerber ◽  
Lorenzo M. Polvani
Keyword(s):  
General Circulation ◽  
Polar Vortex ◽  
Circulation Model ◽  
Stationary Waves ◽  
Stratospheric Polar Vortex ◽  
Stratospheric Sudden Warming ◽  
Annular Modes ◽  
Dynamical Coupling ◽  
The Impact ◽  
Stratospheric Variability

Abstract The impact of stratospheric variability on the dynamical coupling between the stratosphere and the troposphere is explored in a relatively simple atmospheric general circulation model. Variability of the model’s stratospheric polar vortex, or polar night jet, is induced by topographically forced stationary waves. A robust relationship is found between the strength of the stratospheric polar vortex and the latitude of the tropospheric jet, confirming and extending earlier results in the absence of stationary waves. In both the climatological mean and on intraseasonal time scales, a weaker vortex is associated with an equatorward shift in the tropospheric jet and vice versa. It is found that the mean structure and variability of the vortex in the model is very sensitive to the amplitude of the topography and that Northern Hemisphere–like variability, with a realistic frequency of stratospheric sudden warming events, occurs only for a relatively narrow range of topographic heights. When the model captures sudden warming events with fidelity, however, the exchange of information both upward and downward between the troposphere and stratosphere closely resembles that in observations. The influence of stratospheric variability on variability in the troposphere is demonstrated by comparing integrations with and without an active stratosphere. A realistic, time-dependent stratospheric circulation increases the persistence of the tropospheric annular modes, and the dynamical coupling is most apparent prior to and following stratospheric sudden warming events.

scholarly journals A New Look at Stratospheric Sudden Warmings. Part I: Climatology and Modeling Benchmarks

2007 ◽  
Vol 20 (3) ◽  
pp. 449-469 ◽  
Author(s):  
Andrew J. Charlton ◽  
Lorenzo M. Polvani
Keyword(s):  
Numerical Model ◽  
Zonal Wind ◽  
Polar Vortex ◽  
Identification Algorithm ◽  
Event Type ◽  
Stratospheric Polar Vortex ◽  
Stratospheric Sudden Warming ◽  
Model Simulations ◽  
Stratospheric Sudden Warmings ◽  
Dynamical Coupling

Abstract Stratospheric sudden warmings are the clearest and strongest manifestation of dynamical coupling in the stratosphere–troposphere system. While many sudden warmings have been individually documented in the literature, this study aims at constructing a comprehensive climatology: all major midwinter warming events are identified and classified, in both the NCEP–NCAR and 40-yr ECMWF Re-Analysis (ERA-40) datasets. To accomplish this a new, objective identification algorithm is developed. This algorithm identifies sudden warmings based on the zonal mean zonal wind at 60°N and 10 hPa, and classifies them into events that do and do not split the stratospheric polar vortex. Major midwinter stratospheric sudden warmings are found to occur with a frequency of approximately six events per decade, and 46% of warming events lead to a splitting of the stratospheric polar vortex. The dynamics of vortex splitting events is contrasted to that of events where the vortex is merely displaced off the pole. In the stratosphere, the two types of events are found to be dynamically distinct: vortex splitting events occur after a clear preconditioning of the polar vortex, and their influence on middle-stratospheric temperatures lasts for up to 20 days longer than vortex displacement events. In contrast, the influence of sudden warmings on the tropospheric state is found to be largely insensitive to the event type. Finally, a table of dynamical benchmarks for major stratospheric sudden warming events is compiled. These benchmarks are used in a companion study to evaluate current numerical model simulations of the stratosphere.

The impact of the stratosphere on the troposphere during the southern hemisphere stratospheric sudden warming, September 2002

2005 ◽  
Vol 131 (609) ◽  
pp. 2171-2190 ◽  
Author(s):  
A. J. Charlton ◽  
A. O'Neill ◽  
W. A. Lahoz ◽  
A. C. Massacand ◽  
P. Berrisford
Keyword(s):  
Southern Hemisphere ◽  
Stratospheric Sudden Warming ◽  
The Impact

Observed Decadal Changes in Downward Wave Coupling between the Stratosphere and Troposphere in the Southern Hemisphere

2011 ◽  
Vol 24 (17) ◽  
pp. 4558-4569 ◽  
Author(s):  
Nili Harnik ◽  
Judith Perlwitz ◽  
Tiffany A. Shaw
Keyword(s):  
Southern Hemisphere ◽  
Planetary Wave ◽  
Late Winter ◽  
Spectral Correlation ◽  
Dynamical Mechanism ◽  
Wave Coupling ◽  
Reflected Waves ◽  
Dynamical Coupling ◽  
Height Fields ◽  
Reflecting Surface

Downward wave coupling dominates the intraseasonal dynamical coupling between the stratosphere and troposphere in the Southern Hemisphere. The coupling occurs during late winter and spring when the stratospheric basic state forms a well-defined meridional waveguide, which is bounded above by a reflecting surface. This basic-state configuration is favorable for planetary wave reflection and guides the reflected waves back down to the troposphere, where they impact wave structures. In this study decadal changes in downward wave coupling are analyzed using the Modern Era Retrospective-Analysis for Research and Applications (MERRA) dataset. A cross-spectral correlation analysis, applied to geopotential height fields, and a wave geometry diagnostic, applied to zonal-mean zonal wind and temperature data, are used to understand decadal changes in planetary wave propagation. It is found that downward wave 1 coupling from September to December has increased over the last three decades, owing to significant increases at the beginning and end of this 4-month period. The increased downward wave coupling is caused by both an earlier onset of the vertically bounded meridional waveguide configuration and a persistence of this configuration into December. The latter is associated with the observed delay in vortex breakup. The results point to an additional dynamical mechanism whereby the stratosphere has influenced the tropospheric climate in the Southern Hemisphere.

scholarly journals A Very Large, Spontaneous Stratospheric Sudden Warming in a Simple AGCM: A Prototype for the Southern Hemisphere Warming of 2002?

2005 ◽  
Vol 62 (3) ◽  
pp. 890-897 ◽  
Author(s):  
Paul J. Kushner ◽  
Lorenzo M. Polvani
Keyword(s):  
Southern Hemisphere ◽  
Polar Vortex ◽  
Wave Interaction ◽  
Equation Model ◽  
Wave Activity ◽  
Stationary Waves ◽  
Baroclinic Wave ◽  
Primitive Equation ◽  
Stratospheric Sudden Warming ◽  
Insight Into

Abstract An exceptionally strong stratospheric sudden warming (SSW) that spontaneously occurs in a very simple stratosphere–troposphere AGCM is discussed. The model is a dry, hydrostatic, primitive equation model without planetary stationary waves. Transient baroclinic wave–wave interaction in the troposphere thus provides the only source of upward-propagating wave activity into the stratosphere. The model’s SSW is grossly similar to the Southern Hemisphere major SSW of 2002: it occurs after weaker warmings “precondition” the polar vortex for breaking, it involves a split of the polar vortex, and it has a downward-propagating signature. These similarities suggest that the Southern Hemisphere SSW of 2002 might itself have been caused by transient baroclinic wave–wave interaction. The simple model used for this study also provides some insight into how often such extreme events might occur. The frequency distribution of SSWs in the model has exponential, as opposed to Gaussian, tails. This suggests that very large amplitude SSWs, though rare, might occur with higher frequency than might be naively expected.

Southern Hemisphere Seti Survey: Five Years of Project Meta II

1997 ◽  
Vol 161 ◽  
pp. 611-621
Author(s):  
Guillermo A. Lemarchand ◽  
Fernando R. Colomb ◽  
E. Eduardo Hurrell ◽  
Juan Carlos Olalde
Keyword(s):  
Southern Hemisphere ◽  
Scattering Theory ◽  
Galactic Plane ◽  
Narrow Band ◽  
Neutral Hydrogen ◽  
Sky Survey ◽  
Inertial Frames ◽  
Interstellar Scattering ◽  
Extraterrestrial Origin ◽  
Spectral Channels

AbstractProject META II, a full sky survey for artificial narrow-band signals, has been conducted from one of the two 30-m radiotelescopes of the Instituto Argentino de Radioastronomía (IAR). The search was performed near the 1420 Mhz line of neutral hydrogen, using a 8.4 million channels Fourier spectrometer of 0.05 Hz resolution and 400 kHz instantaneous bandwidth. The observing frequency was corrected both for motions with respect to three astronomical inertial frames, and for the effect of Earths rotation, which provides a characteristic changing signature for narrow-band signals of extraterrestrial origin. Among the 2 × 1013spectral channels analyzed, 29 extra-statistical narrow-band events were found, exceeding the average threshold of 1.7 × 10−23Wm−2. The strongest signals that survive culling for terrestrial interference lie in or near the galactic plane. A description of the project META II observing scheme and results is made as well as the possible interpretation of the results using the Cordes-Lazio-Sagan model based in interstellar scattering theory.

Alpha-Effect, Current and Kinetic Helicities for Magnetically Driven Turbulence, and Solar Dynamo

2000 ◽  
Vol 179 ◽  
pp. 387-388
Author(s):  
Gaetano Belvedere ◽  
V. V. Pipin ◽  
G. Rüdiger
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Convection Zone ◽  
Solar Surface ◽  
Momentum Transport ◽  
Angular Momentum Transport ◽  
Magnetic Buoyancy ◽  
Alpha Effect ◽  
Current Helicity

Extended AbstractRecent numerical simulations lead to the result that turbulence is much more magnetically driven than believed. In particular the role ofmagnetic buoyancyappears quite important for the generation ofα-effect and angular momentum transport (Brandenburg & Schmitt 1998). We present results obtained for a turbulence field driven by a (given) Lorentz force in a non-stratified but rotating convection zone. The main result confirms the numerical findings of Brandenburg & Schmitt that in the northern hemisphere theα-effect and the kinetic helicityℋkin= 〈u′ · rotu′〉 are positive (and negative in the northern hemisphere), this being just opposite to what occurs for the current helicityℋcurr= 〈j′ ·B′〉, which is negative in the northern hemisphere (and positive in the southern hemisphere). There has been an increasing number of papers presenting observations of current helicity at the solar surface, all showing that it isnegativein the northern hemisphere and positive in the southern hemisphere (see Rüdigeret al. 2000, also for a review).

The Hemispheric Sign Rule of Current Helicity during the Rising Phase of Cycle 23

2000 ◽  
Vol 179 ◽  
pp. 303-306
Author(s):  
S. D. Bao ◽  
G. X. Ai ◽  
H. Q. Zhang
Keyword(s):  
Solar Cycle ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Active Regions ◽  
Hemispheric Preference ◽  
Current Helicity

AbstractWe compute the signs of two different current helicity parameters (i.e., αbestandHc) for 87 active regions during the rise of cycle 23. The results indicate that 59% of the active regions in the northern hemisphere have negative αbestand 65% in the southern hemisphere have positive. This is consistent with that of the cycle 22. However, the helicity parameterHcshows a weaker opposite hemispheric preference in the new solar cycle. Possible reasons are discussed.

Measurements of the Cape Astrometric Survey of the Southern Hemisphere

1978 ◽  
Vol 48 ◽  
pp. 515-521
Author(s):  
W. Nicholson
Keyword(s):  
Southern Hemisphere ◽  
Automatic Measuring ◽  
Measuring Machine ◽  
Final Selection ◽  
Selection Of

SummaryA routine has been developed for the processing of the 5820 plates of the survey. The plates are measured on the automatic measuring machine, GALAXY, and the measures are subsequently processed by computer, to edit and then refer them to the SAO catalogue. A start has been made on measuring the plates, but the final selection of stars to be made is still a matter for discussion.

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