scholarly journals IMF dependence of high-latitude thermospheric wind pattern derived from CHAMP cross-track measurements

2008 ◽  
Vol 26 (6) ◽  
pp. 1581-1595 ◽  
Author(s):  
M. Förster ◽  
S. Rentz ◽  
W. Köhler ◽  
H. Liu ◽  
S. E. Haaland
Keyword(s):  
Southern Hemisphere ◽  
High Latitude ◽  
Polar Regions ◽  
High Latitudes ◽  
Plasma Convection ◽  
Thermospheric Wind ◽  
Wind Pattern ◽  
Magnetospheric Convection ◽  
Cross Track ◽  
The Imf

Abstract. Neutral thermospheric wind pattern at high latitudes obtained from cross-track acceleration measurements of the CHAMP satellite above both North and South polar regions are statistically analyzed in their dependence on the Interplanetary Magnetic Field (IMF) direction in the GSM y-z plane (clock angle). We compare this dependency with magnetospheric convection pattern obtained from the Cluster EDI plasma drift measurements under the same sorting conditions. The IMF-dependency shows some similarity with the corresponding high-latitude plasma convection insofar that the larger-scale convection cells, in particular the round-shaped dusk cell for ByIMF+ (ByIMF−) conditions at the Northern (Southern) Hemisphere, leave their marks on the dominant general transpolar wind circulation from the dayside to the nightside. The direction of the transpolar circulation is generally deflected toward a duskward flow, in particular in the evening to nighttime sector. The degree of deflection correlates with the IMF clock angle. It is larger for ByIMF+ than for ByIMF− and is systematically larger (~5°) and appear less structured at the Southern Hemisphere compared with the Northern. Thermospheric cross-polar wind amplitudes are largest for BzIMF−/ByIMF− conditions at the Northern Hemisphere, but for BzIMF−/ByIMF+ conditions at the Southern because the magnetospheric convection is in favour of largest wind accelerations over the polar cap under these conditions. The overall variance of the thermospheric wind magnitude at Southern high latitudes is larger than for the Northern. This is probably due to a larger "stirring effect" at the Southern Hemisphere because of the larger distance between the geographic and geomagnetic frameworks.

scholarly journals Simultaneous high- and low-latitude reconnection: ESR and DMSP observations

2002 ◽  
Vol 20 (9) ◽  
pp. 1311-1320 ◽  
Author(s):  
F. Pitout ◽  
P. T. Newell ◽  
S. C. Buchert
Keyword(s):  
High Latitude ◽  
Time Interval ◽  
High Latitudes ◽  
Polar Ionosphere ◽  
Plasma Convection ◽  
Low Latitude ◽  
Svalbard Archipelago ◽  
Cusp Region ◽  
Ionosphere Plasma ◽  
Particle Measurement

Abstract. We present EISCAT Svalbard Radar and DMSP observations of a double cusp during an interval of predominantly northward IMF on 26 November 2000. In the cusp region, the ESR dish, pointing northward, recorded sun-ward ionospheric flow at high latitudes (above 82° GL), indicating reconnection occuring in the magnetospheric lobe. Meanwhile, the same dish also recorded bursts of poleward flow, indicative of bursty reconnection at the subsolar magnetopause. Within this time interval, the DMSP F13 satellite passed in the close vicinity of the Svalbard archipelago. The particle measurement on board exhibited a double cusp structure in which two oppositely oriented ion dispersions are recorded. We interpret this set of data in terms of simultaneous merging at low- and high-latitude magnetopause. We discuss the conditions for which such simultaneous high-latitude and low-latitude reconnection can be anticipated. We also discuss the consequences of the presence of two X-lines in the dayside polar ionosphere.Key words. Magnetospheric physics (solar wind-magnetosphere interactions) – Ionosphere (polar ionosphere; plasma convection)

scholarly journals Southern-Hemisphere high-latitude stratospheric warming revisit

2019 ◽  
Vol 54 (3-4) ◽  
pp. 1671-1682
Author(s):  
Yan Xia ◽  
Weixuan Xu ◽  
Yongyun Hu ◽  
Fei Xie
Keyword(s):  
Southern Hemisphere ◽  
High Latitude ◽  
Recent Decade ◽  
Warming Trend ◽  
High Latitudes ◽  
Stratospheric Warming ◽  
Amundsen Sea ◽  
Maximum Warming ◽  
Dipole Pattern ◽  
The Western Pacific

AbstractPrevious studies showed significant stratospheric warming at the Southern-Hemisphere (SH) high latitudes in September and October over 1979–2006. The warming trend center was located over the Southern Ocean poleward of the Western Pacific in September, with a maximum trend of about 2.8 K/decade. The warming trends in October showed a dipole pattern, with the warming center over the Ross and Amundsen Sea, and the maximum warming trend is about 2.6 K/decade. In the present study, we revisit the problem of the SH stratospheric warming in the recent decade. It is found that the SH high-latitude stratosphere continued warming in September and October over 2007–2017, but with very different spatial patterns. Multiple linear regression demonstrates that ozone increases play an important role in the SH high-latitude stratospheric warming in September and November, while the changes in the Brewer-Dobson circulation contributes little to the warming. This is different from the situation over 1979–2006 when the SH high-latitude stratospheric warming was mainly caused by the strengthening of the Brewer-Dobson circulation and the eastward shift of the warming center. Simulations forced with observed ozone changes over 2007–2017 shows warming trends, suggesting that the observed warming trends over 2007–2017 are at least partly due to ozone recovery. The warming trends due to ozone recovery have important implications for stratospheric, tropospheric and surface climates on SH.

scholarly journals Climate response to imposed solar radiation reductions in high latitudes

2013 ◽  
Vol 4 (2) ◽  
pp. 301-315 ◽  
Author(s):  
M. C. MacCracken ◽  
H.-J. Shin ◽  
K. Caldeira ◽  
G. A. Ban-Weiss
Keyword(s):  
Solar Radiation ◽  
High Latitude ◽  
Energy Transport ◽  
Atmospheric Model ◽  
Cold Season ◽  
Energy Deficit ◽  
Polar Regions ◽  
High Latitudes ◽  
Inter Tropical Convergence Zone ◽  
Equivalent Reduction

Abstract. With human-induced climate change leading to amplified warming in high latitudes, mitigation alone is unlikely to be rapid enough to prevent significant, even irreversible, impacts. Model simulations in which solar insolation was arbitrarily reduced poleward of 51, 61, or 71° latitude in one or both hemispheres not only cooled those regions, but also drew energy from lower latitudes, exerting a cooling influence over much of the particular hemisphere in which the reduction was imposed. The simulations, conducted using the National Center for Atmospheric Research's CAM3.1 atmospheric model coupled to a slab ocean, indicated that high-latitude reductions in absorbed solar radiation have a significantly larger cooling influence than solar reductions of equivalent magnitude spread evenly over the Earth. This amplified influence occurred primarily because concentrated high-latitude reductions in solar radiation led to increased sea ice fraction and surface albedo, thereby amplifying the energy deficit at the top of the atmosphere as compared to the response for an equivalent reduction in solar radiation spread evenly over the globe. Reductions in incoming solar radiation in one polar region (either north or south) resulted in increased poleward energy transport during that hemisphere's cold season and shifted the Inter-Tropical Convergence Zone (ITCZ) away from that pole, whereas comparable solar reductions in both polar regions resulted in increased poleward energy transport, but tended to leave the ITCZ approximately in place. Together, these results suggest that, until emissions reductions are sufficient to limit the warming influence of increasing greenhouse gas concentrations, polar reductions in solar radiation, if they could be efficiently and effectively implemented, warrant further research as an approach to moderating the early stages of both high-latitude and global warming.

scholarly journals High-latitude plasma convection from Cluster EDI: variances and solar wind correlations

2007 ◽  
Vol 25 (7) ◽  
pp. 1691-1707 ◽  
Author(s):  
M. Förster ◽  
G. Paschmann ◽  
S. E. Haaland ◽  
J. M. Quinn ◽  
R. B. Torbert ◽  
...  
Keyword(s):  
Solar Wind ◽  
High Latitude ◽  
Dynamic Pressure ◽  
Propagation Delay ◽  
Auroral Oval ◽  
Linear Increase ◽  
Proton Density ◽  
Plasma Convection ◽  
Latitude Range ◽  
The Imf

Abstract. Based on drift velocity measurements of the EDI instruments on Cluster during the years 2001–2006, we have constructed a database of high-latitude ionospheric convection velocities and associated solar wind and magnetospheric activity parameters. In an earlier paper (Haaland et al., 2007), we have described the method, consisting of an improved technique for calculating the propagation delay between the chosen solar wind monitor (ACE) and Earth's magnetosphere, filtering the data for periods of sufficiently stable IMF orientations, and mapping the EDI measurements from their high-altitude positions to ionospheric altitudes. The present paper extends this study, by looking at the spatial pattern of the variances of the convection velocities as a function of IMF orientation, and by performing sortings of the data according to the IMF magnitude in the GSM y-z plane, |ByzIMF|, the estimated reconnection electric field, Er,sw, the solar wind dynamic pressure, Pdyn, the season, and indices characterizing the ring current (Dst) and tail activity (ASYM-H). The variability of the high-latitude convection shows characteristic spatial patterns, which are mirror symmetric between the Northern and Southern Hemispheres with respect to the IMF By component. The latitude range of the highest variability zone varies with IMF Bz similar to the auroral oval extent. The magnitude of convection standard deviations is of the same order as, or even larger than, the convection magnitude itself. Positive correlations of polar cap activity are found with |ByzIMF| and with Er,sw, in particular. The strict linear increase for small magnitudes of Er,sw starts to deviate toward a flattened increase above about 2 mV/m. There is also a weak positive correlation with Pdyn. At very small values of Pdyn, a secondary maximum appears, which is even more pronounced for the correlation with solar wind proton density. Evidence for enhanced nightside convection during high nightside activity is presented.

scholarly journals Thermospheric vorticity at high geomagnetic latitudes from CHAMP data and its IMF dependence

2011 ◽  
Vol 29 (1) ◽  
pp. 181-186 ◽  
Author(s):  
M. Förster ◽  
S. E. Haaland ◽  
E. Doornbos
Keyword(s):  
Ionospheric Plasma ◽  
Outer Boundary ◽  
Polar Regions ◽  
Wind Pattern ◽  
Champ Satellite ◽  
Average Wind ◽  
Average Current ◽  
Statistical Studies ◽  
Cross Track ◽  
Champ Data

Abstract. Neutral thermospheric wind pattern at high latitudes obtained from cross-track acceleration measurements of the CHAMP satellite above both polar regions are used to deduce statistical neutral wind vorticity distributions and were analyzed in their dependence on the Interplanetary Magnetic Field (IMF). The average pattern confirms the large duskside anticyclonic vortex seen in the average wind pattern and reveals a cyclonic vorticity on the dawnside, which is almost equal in magnitude to the duskside minimum. The outer shape of the vorticity pattern agrees approximately with the outer boundary of region-1 currents in the well-known average current distributions of Iijima and Potemra (1976) The IMF dependence of the vorticity pattern resembles the characteristic FAC and ionospheric plasma drift pattern known from various statistical studies obtained under the same sorting conditions.

scholarly journals Dayside flow bursts and high-latitude reconnection when the IMF is strongly northward

2006 ◽  
Vol 24 (8) ◽  
pp. 2227-2242 ◽  
Author(s):  
H. Hu ◽  
T. K. Yeoman ◽  
M. Lester ◽  
R. Liu ◽  
H. Yang ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
High Latitude ◽  
Closed Field ◽  
Flow Data ◽  
Plasma Convection ◽  
Convection Pattern ◽  
Reconnection Rate ◽  
Northern Hemispheric ◽  
Field Lines

Abstract. The characteristics of dayside ionospheric convection are studied using Northern Hemispheric SuperDARN data and DMSP particle and flow observations when the interplanetary magnetic field (IMF) was strongly northward during 13:00–15:00 UT on 2 March 2002. Although IMF Bx was positive, which is believed to favour Southern Hemisphere high-latitude reconnection at equinox, a four-cell convection pattern was observed and lasted for more than 1.5 h in the Northern Hemisphere. The reconnection rate derived from an analysis of the Northern Hemisphere SuperDARN data illustrates that the high-latitude reconnection was quasi-periodic, with a period between 4–16 min. A sawtooth-like and reverse-dispersed ion signature was observed by DMSP-F14 in the sunward cusp convection at around 14:41 UT, confirming that the high-latitude reconnection was pulsed. Accompanying the pulsed reconnection, strong antisunward ionospheric flow bursts were observed in the post-noon LLBL region on closed field lines, propagating with the same speed as the plasma convection. DMSP flow data show that a similar flow pattern and particle precipitation occurred in the conjugate Southern Hemisphere.

scholarly journals Evolution of high-latitude biotas

1992 ◽  
Vol 6 ◽  
pp. 71-71
Author(s):  
J. Alistair Crame
Keyword(s):  
High Latitude ◽  
Fossil Record ◽  
A Priori ◽  
Cladistic Analysis ◽  
Distribution Patterns ◽  
Polar Regions ◽  
High Latitudes ◽  
Rapid Improvement ◽  
Low Latitudes ◽  
Early Neogene

With the recent rapid improvement in the quality of the fossil record in both polar regions it has become possible to examine critically the development of high-latitude faunas and floras through time. Within arctic regions, distinctive biotas have been present, at least intermittently, since the early Permian, and in antarctic regions they can be traced back to the early Middle Devonian. It would appear that, whenever continents (and continental shelves) moved into the high latitudes they were the sites of significant biotic differentiation.To investigate the ways in which taxa may have accumulated in the high latitudes through time, three simple global models have been proposed. In the first of these it is envisaged that major groups of plants and animals arose in the low latitudes and disseminated subsequently into the polar regions. Here they would become relicts and the latter would be regarded as refugia. The second model is almost exactly the reverse of the first in that it proposes that certain taxa arose in the polar regions and then spread, through time, into the low latitudes. Such a process may at first sight seem less likely, but the Antarctic fossil record in particular is providing important evidence to suggest that certain major groups of both plants and animals had a high-latitude origin. The third model differs substantially from the previous two in that it makes no a priori assumptions about either centres of origin or the process of dispersal. It merely states that, at certain times in the past, widespread distribution patterns have been disrupted in the low latitudes to form disjunct populations in the northern and southern hemispheres. It results in the classic bipolar pattern, which can now be traced back to at least the Early Jurassic period.A major phase of Jurassic - Cretaceous bipolarity can be attributed to tectonic vicariance as the Pangean supercontinent disintegrated, and a major late Paleogene - early Neogene one can be related to climatic vicariance. Such hypotheses are attractive as they are testable by cladistic analysis. Although data available so far are limited, both fossil and living benthic molluscs offer considerable scope for future work.

scholarly journals Dayside convection and auroral morphology during an interval of northward interplanetary magnetic field

2000 ◽  
Vol 18 (4) ◽  
pp. 436-444 ◽  
Author(s):  
S. E. Milan ◽  
M. Lester ◽  
S. W. H. Cowley ◽  
M. Brittnacher
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
High Latitude ◽  
Auroral Oval ◽  
Large Field ◽  
Convection Flow ◽  
Plasma Convection ◽  
Flow Measurements ◽  
Auroral Emission ◽  
The Imf

Abstract. We investigate the dayside auroral dynamics and ionospheric convection during an interval when the interplanetary magnetic field (IMF) had predominantly a positive Bz component (northward IMF) but varying By. Polar UVI observations of the Northern Hemisphere auroral emission indicate the existence of a region of luminosity near local noon at latitudes poleward of the dayside auroral oval, which we interpret as the ionospheric footprint of a high-latitude reconnection site. The large field-of-view afforded by the satellite-borne imager allows an unprecedented determination of the dynamics of this region, which has not previously been possible with ground-based observations. The location of the emission in latitude and magnetic local time varies in response to changes in the orientation of the IMF; the cusp MLT and the IMF By component are especially well correlated, the emission being located in the pre- or post-noon sectors for By < 0 nT or By > 0 nT, respectively. Simultaneous ground-based observations of the ionospheric plasma drift are provided by the CUTLASS Finland HF coherent radar. For an interval of IMF By \\approx 0 nT, these convection flow measurements suggest the presence of a clockwise-rotating lobe cell contained within the pre-noon dayside polar cap, with a flow reversal closely co-located with the high-latitude luminosity region. This pattern is largely consistent with recent theoretical predictions of the convection flow during northward IMF. We believe that this represents the first direct measurement of the convection flow at the imaged location of the footprint of the high-latitude reconnection site.Key words: Magnetospheric physics (auroral phenomena; magnetopause · cusp · and boundary layers; plasma convection)

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