Low Latitude Vorticity Injections and the Development of Large Scale Anomalous Circulation Patterns

Some general characteristics of synoptic developments in the 500 mb vorticity field are discussed with particular attention devoted to sudden injections of vorticity and to changes in circulation patterns downwind therefrom. Attention is then focused on vorticity injections generated at low latitudes, but not too low to interact in an important way with the middle latitude circulation. Composite maps based upon numerous cases are shown which reveal the development of large scale anomalous patterns in the westerlies during the 3 days subsequent to low latitude vorticity injection. The forecasting implications are discussed.

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Magnetopause reconnection across wide local time

Annales Geophysicae ◽

10.5194/angeo-29-1683-2011 ◽

2011 ◽

Vol 29 (9) ◽

pp. 1683-1697 ◽

Cited By ~ 45

Author(s):

M. W. Dunlop ◽

Q.-H. Zhang ◽

Y. V. Bogdanova ◽

K. J. Trattner ◽

Z. Pu ◽

...

Keyword(s):

Magnetic Reconnection ◽

Large Scale ◽

Double Star ◽

Local Times ◽

Low Latitude ◽

Guide Field ◽

Dayside Magnetopause ◽

Wide Range ◽

Low Latitudes ◽

Local Noon

Abstract. During April to July 2007 a combination of 10 spacecraft provided simultaneous monitoring of the dayside magnetopause across a wide range of local times. The array of four Cluster spacecraft, separated at large distances (10 000 km), were traversing the dawn-side magnetopause at high and low latitudes; the five THEMIS spacecraft were often in a 4 + 1 grouped configuration, traversing the low latitude, dusk-side magnetosphere, and the Double star, TC-1 spacecraft was in an equatorial orbit between the local times of the THEMIS and Cluster orbits. We show here a number of near simultaneous conjunctions of all 10 spacecraft at the magnetopause. One conjunction identifies an extended magnetic reconnection X-line, tilted in the low latitude, sub-solar region, which exists together with active anti-parallel reconnection sites extending to locations on the dawn-side flank. Oppositely moving FTE's are observed on all spacecraft, consistent with the initially strong IMF By conditions and the comparative locations of the spacecraft both dusk-ward and dawn-ward of noon. Comparison with other conjunctions of magnetopause crossings, which are also distributed over wide local times, supports the result that reconnection activity may occur at many sites simultaneously across the sub-solar and flank magnetopause, but linked to the large scale (extended) configuration of the merging line; broadly depending on IMF orientation. The occurrence of MR therefore inherently follows a "component" driven scenario irrespective of the guide field conditions. Some conjunctions allow the global magnetopause response to IMF changes to be observed and the distribution of spacecraft can directly confirm its shape, motion and deformation at local noon, dawn and dusk-side, simultaneously.

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Comparative investigations of equatorial electrodynamics and low-to-mid latitude coupling of the thermosphere-ionosphere system

Annales Geophysicae ◽

10.5194/angeo-24-503-2006 ◽

2006 ◽

Vol 24 (2) ◽

pp. 503-513 ◽

Cited By ~ 29

Author(s):

M. J. Colerico ◽

M. Mendillo ◽

C. G. Fesen ◽

J. Meriwether

Keyword(s):

General Circulation ◽

Large Scale ◽

Circulation Model ◽

Upper Atmosphere ◽

Low Latitude ◽

Brightness Wave ◽

F Region ◽

Fabry Perot ◽

Low Latitudes ◽

First Time

Abstract. The thermospheric midnight temperature maximum (MTM) is a highly variable, but persistent, large scale neutral temperature enhancement which occurs at low latitudes. Its occurrence can impact many fundamental upper atmospheric parameters such as pressure, density, neutral winds, neutral density, and F-region plasma. Although the MTM has been the focus of several investigations employing various instrumentation including photometers, satellites, and Fabry-Perot interferometers, limited knowledge exists regarding the latitude extent of its influence on the upper atmosphere. This is largely due to observational limitations which confined the collective geographic range to latitudes within ±23°. This paper investigates the MTM's latitudinal extent through all-sky imaging observations of its 6300Å airglow signature referred to by Colerico et al. (1996) as the midnight brightness wave (MBW). The combined field of view of three Southern Hemisphere imaging systems located at Arequipa, Peru, and Tucuman and El Leoncito, Argentina, for the first time extends the contiguous latitudinal range of imager observations to 8° S-39° S in the American sector. Our results highlight the propagation of MBW events through the combined fields of view past 39° S latitude, providing the first evidence that the MTM's effect on the upper atmosphere extends into mid-latitudes. The observations presented here are compared with modeled 6300Å emissions calculated using the NCAR thermosphere-ionosphere-electrodynamic general circulation model (TIEGCM) in conjunction with an airglow code. We report that at this time TIEGCM is unable to simulate an MBW event due to the model's inability to reproduce an MTM of the same magnitude and occurrence time as those observed via FPI measurements made from Arequipa. This work also investigates the origins of an additional low latitude airglow feature referred to by Colerico et al. (1996) as the pre-midnight brightness wave (PMBW) and described as an enhancement in 6300Å emission which occurs typically between 20:00-22:00 LT and exhibits equatorward propagation. We present the first successful simulation of a PMBW event using the TIEGCM and the airglow code. We find that the PMBW's origin is electro-dynamical in nature, resulting from the expected evening decay of the inter-tropical arcs.

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The characteristics of transforming coordinates from the geocentric system WGS-84 for the Mercator projection under low latitudes conditions

Geodesy and Cartography ◽

10.22389/0016-7126-2018-940-10-2-6 ◽

2018 ◽

Vol 940 (10) ◽

pp. 2-6

Author(s):

J.A. Younes ◽

M.G. Mustafin

Keyword(s):

Coordinate System ◽

Satellite System ◽

Programming Algorithm ◽

Low Latitude ◽

Model Calculations ◽

Mercator Projection ◽

Low Latitudes ◽

Rectangular Coordinates ◽

Global Navigation Satellite ◽

Coordination Methods

The issue of calculating the plane rectangular coordinates using the data obtained by the satellite observations during the creation of the geodetic networks is discussed in the article. The peculiarity of these works is in conversion of the coordinates into the Mercator projection, while the plane coordinate system on the base of Gauss-Kruger projection is used in Russia. When using the technology of global navigation satellite system, this task is relevant for any point (area) of the Earth due to a fundamentally different approach in determining the coordinates. The fact is that satellite determinations are much more precise than the ground coordination methods (triangulation and others). In addition, the conversion to the zonal coordinate system is associated with errors; the value at present can prove to be completely critical. The expediency of using the Mercator projection in the topographic and geodetic works production at low latitudes is shown numerically on the basis of model calculations. To convert the coordinates from the geocentric system with the Mercator projection, a programming algorithm which is widely used in Russia was chosen. For its application under low-latitude conditions, the modification of known formulas to be used in Saudi Arabia is implemented.

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Barotropic Regeneration of Upper-Level Synoptic Disturbances in Different Configurations of the Zonal Weather Regime

Journal of the Atmospheric Sciences ◽

10.1175/2008jas2603.1 ◽

2008 ◽

Vol 65 (10) ◽

pp. 3159-3178 ◽

Cited By ~ 10

Author(s):

Gwendal Rivière

Keyword(s):

Large Scale ◽

Deformation Field ◽

Regeneration Process ◽

Barotropic Model ◽

Weather Regime ◽

The North ◽

The Difference ◽

Upper Level ◽

Composite Maps ◽

Large Scale Flow

Barotropic dynamics of upper-tropospheric midlatitude disturbances evolving in different configurations of the zonal weather regime (i.e., in different zonal-like large-scale flows) were studied using observational analyses and barotropic model experiments. The contraction stage of upper-level disturbances that follows their elongation stage leads to an increase of eddy kinetic energy that is called the barotropic regeneration process in this text. This barotropic mechanism is studied through notions of barotropic critical regions (BtCRs) and effective deformation that have been introduced in a previous paper. The effective deformation field is equal to the difference between the square of the large-scale deformation magnitude and the square of the large-scale vorticity. Regions where the effective deformation is positive correspond to regions where the large-scale flow tends to strongly stretch synoptic disturbances. A BtCR is an area separating two large-scale regions of positive effective deformation, one located upstream and on the south side of the jet and the other downstream and on the north side. Such a region presents a discontinuity in the orientation of the dilatation axes and is a potential area where the barotropic regeneration process may occur. Winter days presenting a zonal weather regime in the 40-yr ECMWF Re-Analysis dataset are decomposed, via a partitioning algorithm, into different configurations of the effective deformation field at 300 hPa. A six-cluster partition is obtained. Composite maps of the barotropic generation rate for each cluster exhibit a succession of negative and positive values on both sides of the BtCRs. It confirms statistically that the barotropic regeneration mechanism occurs preferentially about BtCRs. Numerical experiments using a forced barotropic model on the sphere are performed. Each experiment consists of adding a synoptic-scale perturbation to one of the zonal-like jet configurations found in observations, which is kept fixed with time. The combined effects of the effective deformation and nonlinearities are shown to be crucial to reproduce the barotropic regeneration process about BtCRs.

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Six-fold increase in historical Northern Hemisphere concurrent large heatwaves driven by warming and changing atmospheric circulations

Journal of Climate ◽

10.1175/jcli-d-21-0200.1 ◽

2021 ◽

pp. 1-39

Author(s):

Cassandra D.W. Rogers ◽

Kai Kornhuber ◽

Sarah E. Perkins-Kirkpatrick ◽

Paul C. Loikith ◽

Deepti Singh

Keyword(s):

Northern Hemisphere ◽

Large Scale ◽

Warm Season ◽

Fold Increase ◽

Circulation Pattern ◽

Positive Influence ◽

Climate Risks ◽

Circulation Patterns ◽

Multiple Regions ◽

Barents And Kara Seas

AbstractSimultaneous heatwaves affecting multiple regions (referred to as concurrent heatwaves), pose compounding threats to various natural and societal systems, including global food chains, emergency response systems, and reinsurance industries. While anthropogenic climate change is increasing heatwave risks across most regions, the interactions between warming and circulation changes that yield concurrent heatwaves remain understudied. Here, we quantify historical (1979-2019) trends in concurrent heatwaves during the warm-season (May-September, MJJAS) across the Northern Hemisphere mid- to high-latitudes. We find a significant increase of ~46% in the mean spatial extent of concurrent heatwaves, ~17% increase in their maximum intensity, and ~6-fold increase in their frequency. Using Self-Organising Maps, we identify large-scale circulation patterns (300 hPa) associated with specific concurrent heatwave configurations across Northern Hemisphere regions. We show that observed changes in the frequency of specific circulation patterns preferentially increase the risk of concurrent heatwaves across particular regions. Patterns linking concurrent heatwaves across eastern North America, eastern and northern Europe, parts of Asia, and the Barents and Kara Seas, show the largest increases in frequency (~5.9 additional days per decade). We also quantify the relative contributions of circulation pattern changes and warming to overall observed concurrent heatwave day frequency trends. While warming has a predominant and positive influence on increasing concurrent heatwaves, circulation pattern changes have a varying influence and account for up to 0.8 additional concurrent heatwave days per decade. Identifying regions with an elevated risk of concurrent heatwaves and understanding their drivers is indispensable for evaluating projected climate risks on interconnected societal systems and fostering regional preparedness in a changing climate.

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Case study on total electron content enhancements at low latitudes during low geomagnetic activities before the storms

Annales Geophysicae ◽

10.5194/angeo-26-893-2008 ◽

2008 ◽

Vol 26 (4) ◽

pp. 893-903 ◽

Cited By ~ 27

Author(s):

◽

Keyword(s):

Total Electron Content ◽

Geomagnetic Activity ◽

Electron Content ◽

Low Latitude ◽

Total Electron ◽

Defense Meteorological Satellite Program ◽

Low Latitudes ◽

Global Ionospheric Maps ◽

Geomagnetic Activities

Abstract. Sometimes the ionospheric total electron content (TEC) is significantly enhanced during low geomagnetic activities before storms. In this article, we investigate the characteristics of those interesting TEC enhancements using regional and global TEC data. We analyzed the low-latitude TEC enhancement events that occurred around longitude 120° E on 10 February 2004, 21 January 2004, and 4 March 2001, respectively. The TEC data are derived from regional Global Positioning System (GPS) observations in the Asia/Australia sector as well as global ionospheric maps (GIMs) produced by Jet Propulsion Laboratory (JPL). Strong enhancements under low geomagnetic activity before the storms are simultaneously presented at low latitudes in the Asia/Australia sector in regional TEC and JPL GIMs. These TEC enhancements are shown to be regional events with longitudinal and latitudinal extent. The regions of TEC enhancements during these events are confined at narrow longitude ranges around longitude 120° E. The latitudinal belts of maxima of enhancements locate around the northern and southern equatorial ionization anomaly (EIA) crests, which are consistent with those low-latitude events presented by Liu et al. (2008). During the 4 March 2001 event, the total plasma density Ni observed by the Defense Meteorological Satellite Program (DMSP) spacecraft F13 at 840 km altitude are of considerably higher values on 4 March than on the previous day in the TEC enhanced regions. Some TEC enhancement events are possibly due to contributions from auroral/magnetospheric origins; while there are also quasi-periodic enhancement events not related to geomagnetic activity and associated probably with planetary wave type oscillations (e.g. the 6 January 1998 event). Further investigation is warrented to identify/separate contributions from possible sources.

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Obliquity forcing of low-latitude climate

Climate of the Past Discussions ◽

10.5194/cpd-11-221-2015 ◽

2015 ◽

Vol 11 (1) ◽

pp. 221-241 ◽

Cited By ~ 4

Author(s):

J. H. C. Bosmans ◽

F. J. Hilgen ◽

E. Tuenter ◽

L. J. Lourens

Keyword(s):

High Latitude ◽

Climate Model ◽

Global Climate ◽

Global Climate Model ◽

Rotational Axis ◽

Low Latitude ◽

Low Latitudes ◽

Paleoclimate Records ◽

Induced Changes ◽

The Tropics

Abstract. The influence of obliquity, the tilt of the Earth's rotational axis, on incoming solar radiation at low latitudes is small, yet many tropical and subtropical paleoclimate records reveal a clear obliquity signal. Several mechanisms have been proposed to explain this signal, such as the remote influence of high-latitude glacials, the remote effect of insolation changes at mid- to high latitudes independent of glacial cyclicity, shifts in the latitudinal extent of the tropics, and changes in latitudinal insolation gradients. Using a sophisticated coupled ocean–atmosphere global climate model, EC-Earth, without dynamical ice sheets, we performed two experiments of obliquity extremes. Our results show that obliquity-induced changes in tropical climate can occur without high-latitude ice sheet fluctuations. Furthermore, the tropical circulation changes are consistent with obliquity-induced changes in the cross-equatorial insolation gradient, implying that this gradient may be used to explain obliquity signals in low-latitude paleoclimate records instead of the classic 65° N summer insolation curve.

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Dominant Large-Scale Atmospheric Circulation Systems for the Extreme Precipitation over the Western Sichuan Basin in Summer 2013

Advances in Meteorology ◽

10.1155/2015/690363 ◽

2015 ◽

Vol 2015 ◽

pp. 1-10 ◽

Cited By ~ 2

Author(s):

Yamin Hu ◽

Panmao Zhai ◽

Lihong Liu ◽

Yang Chen ◽

Yanju Liu

Keyword(s):

Extreme Precipitation ◽

Sichuan Basin ◽

Large Scale ◽

Function Technique ◽

Western Sichuan ◽

Cold Flow ◽

Circulation Patterns ◽

Anomalous Anticyclone ◽

Western Sichuan Basin ◽

Large Scale Atmospheric Circulation

The western Sichuan Basin (WSB) is a rainstorm center influenced by complicated factors such as topography and circulation. Based on multivariable empirical orthogonal function technique for extreme precipitation processes (EPP) in WSB in 2013, this study reveals the dominant circulation patterns. Results indicate that the leading modes are characterized by “Saddle” and “Sandwich” structures, respectively. In one mode, a TC from the South China Sea (SCS) converts into the inverted trough and steers warm moist airflow northward into the WSB. At the same time, WPSH extends westward over the Yangtze River and conveys a southeasterly warm humid flow. In the other case, WPSH is pushed westward by TC in the Western Pacific and then merges with an anomalous anticyclone over SCS. The anomalous anticyclone and WPSH form a conjunction belt and convey the warm moist southwesterly airflow to meet with the cold flow over the WSB. The configurations of WPSH and TC in the tropic and the blocking and trough in the midhigh latitudes play important roles during the EPPs over the WSB. The persistence of EPPs depends on the long-lived large-scale circulation configuration steady over the suitable positions.

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Statistical correlation of spectral broadening in VLF transmitter signal and low-frequency ionospheric turbulence from observation on DEMETER satellite

Natural Hazards and Earth System Science ◽

10.5194/nhess-8-1105-2008 ◽

2008 ◽

Vol 8 (5) ◽

pp. 1105-1111 ◽

Cited By ~ 7

Author(s):

A. Rozhnoi ◽

M. Solovieva ◽

O. Molchanov ◽

O. Akentieva ◽

J. J. Berthelier ◽

...

Keyword(s):

Middle Latitude ◽

Statistical Correlation ◽

Occurrence Rate ◽

Signal Spectrum ◽

Ionospheric Turbulence ◽

Low Latitude ◽

Demeter Satellite ◽

Ion Cyclotron ◽

Latitude Region

Abstract. In our earlier papers we have found the effect of VLF transmitter signal depression over epicenters of the large earthquakes from observation on the French DEMETER satellite that can be considered as new method of global diagnostics of seismic influence on the ionosphere. At present paper we investigate a possibility VLF signal-ionospheric turbulence interaction using additional characteristic of VLF signal-spectrum broadening. This characteristic is important for estimation of the interaction type: linear or nonlinear scattering. Our main results are the following: – There are two zones of increased spectrum broadening, which are centered near magnetic latitudes Φ=±10° and Φ=±40°. Basing on the previous case study research and ground ionosonde registrations, probably it is evidence of nonlinear (active) scattering of VLF signal on the ionospheric turbulence. However occurrence rate of spectrum broadening in the middle-latitude area is higher than in the near-equatorial zone (~15–20% in comparison with ~100% in former area) that is probably coincides with the rate of ionospheric turbulence. – From two years statistics of observation in the selected 3 low-latitude regions and 1 middle-latitude region inside reception area of VLF signal from NWC transmitter we find a correlation of spectrum broadening neither with ion-cyclotron noise (f=150–500 Hz), which possibly means poor representation of the turbulence by the noise due to its mixture with natural ELF emission (which correlates with whistler), nor with magnetic storm activity. – We find rather evident correlation of ion-cyclotron frequency noise, VLF signal depression and weak correlation of spectrum broadening with seismicity in the middle-latitude region over Japan. But in the low-latitude regions we do not find such a correlation. Statistical decrease of VLF signal supports our previous case study results. However rather weak spectrum broadening-seismicity statistical correlation means probably that passive scattering prevails upon nonlinear (active) one.

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