scholarly journals Southern Hemisphere climate variability forced by Northern Hemisphere ice-sheet topography

Nature ◽  
2018 ◽  
Vol 554 (7692) ◽  
pp. 351-355 ◽  
Author(s):  
T. R. Jones ◽  
W. H. G. Roberts ◽  
E. J. Steig ◽  
K. M. Cuffey ◽  
B. R. Markle ◽  
...  
Keyword(s):  
Climate Variability ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Ice Sheet ◽  
Ice Sheet Topography

scholarly journals A new approach for simulating the paleo evolution of the Northern Hemisphere ice sheets

2017 ◽  
Author(s):  
Rubén Banderas ◽  
Jorge Alvarez-Solas ◽  
Alexander Robinson ◽  
Marisa Montoya
Keyword(s):  
Climate Variability ◽  
Northern Hemisphere ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Last Glacial Period ◽  
New Approach ◽  
Anomaly Field ◽  
Ice Volume ◽  
The Last Glacial ◽  
Millennial Scale

Abstract. The aim of this study is to assess and improve the methods currently used to force ice sheet models offline. To this end, three different synthetic transient forcing climatologies are developed for the past 120 kyr following a perturbative approach and applied to an ice-sheet model. The results are used to evaluate their consequences for simulating the paleo evolution of the Northern Hemisphere ice sheets. The first method follows the usual approach in which temperature anomalies relative to present are calculated by combining a present-day climatology with a simulated glacial-interglacial climatic anomaly field interpolated through an index derived from ice-core data. In the second approach the representation of millennial-scale climate variability is improved by incorporating a simulated stadial-interstadial anomaly field. The third is a refinement of the second one in which the amplitudes of both orbital and millennial-scale variations are corrected to provide a perfect agreement with a recent absolute temperature reconstruction over Greenland. The comparison of the three climate forcing methods highlights the tendency of the usual approach to overestimate the temperature variability over North America and Eurasia at millennial timescales. This leads to a relatively high Northern Hemisphere (NH) ice-volume variability on these timescales. Through enhanced ablation, this results in too low an ice volume throughout the last glacial period (LGP), below or at the lower end of the uncertainty range of estimations. Improving the representation of millennial-scale variability alone yields an important increase of ice volume in all NH ice sheets, but especially in the Fennoscandian ice sheet (FIS). Optimizing the amplitude of the temperature anomalies to match the Greenland reconstruction results in a further increase of the simulated ice-sheet volume throughout the LGP. Our new method provides a more realistic representation of orbital and millennial scale climate variability and represents an improvement in the transient forcing of ice sheets during the last glacial period. Interestingly, our new approach underestimates ice-volume variations on millennial timescales as indicated by sea-level records. This suggests that either the origin of the latter is not the NH or that processes not represented in our study, notably variations in oceanic conditions, need to be invoked to account for an important role of millennial-scale climate variability on millennial-scale ice- volume fluctuations. We finally provide here both our derived climate evolution of the LGP using the three methods as well as the resulting ice-sheet configurations. These could be of interest for future studies dealing with the atmospheric or/and oceanic consequences of transient ice-sheet evolution throughout the LGP, and as a source of climate input to other ice sheet models.

scholarly journals A theory of Pleistocene glacial rhythmicity

2018 ◽  
Vol 9 (3) ◽  
pp. 1025-1043 ◽  
Author(s):  
Mikhail Y. Verbitsky ◽  
Michel Crucifix ◽  
Dmitry M. Volobuev
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Late Pleistocene ◽  
Positive Feedback ◽  
Ice Sheet ◽  
Nonlinear Regime ◽  
Early Pleistocene ◽  
System Response ◽  
Astronomical Forcing ◽  
The Antarctic

Abstract. Variations in Northern Hemisphere ice volume over the past 3 million years have been described in numerous studies and well documented. These studies depict the mid-Pleistocene transition from 40 kyr oscillations of global ice to predominantly 100 kyr oscillations around 1 million years ago. It is generally accepted to attribute the 40 kyr period to astronomical forcing and to attribute the transition to the 100 kyr mode to a phenomenon caused by a slow trend, which around the mid-Pleistocene enabled the manifestation of nonlinear processes. However, both the physical nature of this nonlinearity and its interpretation in terms of dynamical systems theory are debated. Here, we show that ice-sheet physics coupled with a linear climate temperature feedback conceal enough dynamics to satisfactorily explain the system response over the full Pleistocene. There is no need, a priori, to call for a nonlinear response of the carbon cycle. Without astronomical forcing, the obtained dynamical system evolves to equilibrium. When it is astronomically forced, depending on the values of the parameters involved, the system is capable of producing different modes of nonlinearity and consequently different periods of rhythmicity. The crucial factor that defines a specific mode of system response is the relative intensity of glaciation (negative) and climate temperature (positive) feedbacks. To measure this factor, we introduce a dimensionless variability number, V. When positive feedback is weak (V∼0), the system exhibits fluctuations with dominating periods of about 40 kyr which is in fact a combination of a doubled precession period and (to smaller extent) obliquity period. When positive feedback increases (V∼0.75), the system evolves with a roughly 100 kyr period due to a doubled obliquity period. If positive feedback increases further (V∼0.95), the system produces fluctuations of about 400 kyr. When the V number is gradually increased from its low early Pleistocene values to its late Pleistocene value of V∼0.75, the system reproduces the mid-Pleistocene transition from mostly 40 kyr fluctuations to a 100 kyr period rhythmicity. Since the V number is a combination of multiple parameters, it implies that multiple scenarios are possible to account for the mid-Pleistocene transition. Thus, our theory is capable of explaining all major features of the Pleistocene climate, such as the mostly 40 kyr fluctuations of the early Pleistocene, a transition from an early Pleistocene type of nonlinear regime to a late Pleistocene type of nonlinear regime, and the 100 kyr fluctuations of the late Pleistocene. When the dynamical climate system is expanded to include Antarctic glaciation, it becomes apparent that climate temperature positive feedback (or its absence) plays a crucial role in the Southern Hemisphere as well. While the Northern Hemisphere insolation impact is amplified by the outside-of-glacier climate and eventually affects Antarctic surface and basal temperatures, the Antarctic ice-sheet area of glaciation is limited by the area of the Antarctic continent, and therefore it cannot engage in strong positive climate feedback. This may serve as a plausible explanation for the synchronous response of the Northern and Southern Hemisphere to Northern Hemisphere insolation variations. Given that the V number is dimensionless, we consider that this model could be used as a framework to investigate other physics that may possibly be involved in producing ice ages. In such a case, the equation currently representing climate temperature would describe some other climate component of interest, and as long as this component is capable of producing an appropriate V number, it may perhaps be considered a feasible candidate.

Global Ice-Sheet System Interlocked by Sea Level

1986 ◽  
Vol 26 (1) ◽  
pp. 3-26 ◽  
Author(s):  
George H. Denton ◽  
Terence J. Hughes ◽  
Wibjörn Karlén
Keyword(s):  
Carbon Dioxide ◽  
Sea Level ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
North Atlantic ◽  
High Frequency ◽  
Atmospheric Carbon Dioxide ◽  
Ice Sheet ◽  
Ice Age ◽  
Atmospheric Carbon

Denton and Hughes (1983, Quaternary Research 20, 125–144) postulated that sea level linked a global ice-sheet system with both terrestrial and grounded marine components during late Quaternary ice ages. Summer temperature changes near Northern Hemisphere melting margins initiated sea-level fluctuations that controlled marine components in both polar hemispheres. It was further proposed that variations of this ice-sheet system amplified and transmitted Milankovitch summer half-year insolation changes between 45 and 75°N into global climatic changes. New tests of this hypothesis implicate sea level as a major control of the areal extent of grounded portions of the Antarctic Ice Sheet, thus fitting the concept of a globally interlocked ice-sheet system. But recent atmospheric modeling results (Manabe and Broccoli, 1985, Journal of Geophysical Research 90, 2167–2190) suggest that factors other than areal changes of the grounded Antarctic Ice Sheet strongly influenced Southern Hemisphere climate and terminated the last ice age simultaneously in both polar hemispheres. Atmospheric carbon dioxide linked to high-latitude oceans is the most likely candidate (Shackleton and Pisias, 1985, Atmospheric carbon dioxide, orbital forcing, and climate. In “The Carbon Cycle and Atmospheric CO2: Natural Variations Archean to Present” (E. T. Sundquest and W. S. Broecker, Eds.), pp. 303–318. Geophysical Monograph 32, American Geophysical Union, Washington, D.C.), but another potential influence was high-frequency climatic oscillations (2500 yr). It is postulated that variations in atmospheric carbon dioxide acted through an Antarctic ice shelf linked to the grounded ice sheet to produce and terminate Southern Hemisphere ice-age climate. It is further postulated that Milankovitch summer insolation combined with a warm high-frequency oscillation caused marked recession of Northern Hemisphere ice-sheet melting margins and the North Atlantic polar front about 14,000 14C yr B.P. This permitted renewed formation of North Atlantic Deep Water, which could well have controlled atmospheric carbon dioxide (W. S. Broecker, D. M. Peteet, and D. Rind, 1985, Nature (London) 315, 21–26). Combined melting and consequent sea-level rise from the three warming factors initiated irreversible collapse of the interlocked global ice-sheet system, which was at its largest but most vulnerable configuration.

scholarly journals Recent warming inconsistent with natural association between temperature and atmospheric circulation over the last 2000 years

2006 ◽  
Vol 2 (3) ◽  
pp. 327-355 ◽  
Author(s):  
P. A. Mayewski ◽  
K. A. Maasch
Keyword(s):  
Climate Variability ◽  
Atmospheric Circulation ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
High Latitude ◽  
Natural Climate Variability ◽  
The Past ◽  
Past 2000 Years ◽  
Hemisphere Temperature ◽  
Natural Climate

Abstract. Comparison between proxies for atmospheric circulation and temperature reveals associations over the last few decades that are inconsistent with those of the past 2000 years. Notably, patterns of middle to high latitude atmospheric circulation in both hemispheres are still within the range of variability of the last 6–10 centuries while, as demonstrated by Mann and Jones (2003), Northern Hemisphere temperatures over recent decades are the highest of the last 2000 years. Further, recent temperature change precedes change in middle to high latitude atmospheric circulation unlike the two most notable changes in climate of the past 2000 years during which change in atmospheric circulation preceded or coincided with change in temperature. In addition, the most prominent change in Southern Hemisphere temperature and atmospheric circulation of the past 2000, and probably 9000 years, precedes change in temperature and atmospheric circulation in the Northern Hemisphere unlike the recent change in Northern Hemisphere temperature that leads. These findings provide new verification that recent rise in temperature is inconsistent with natural climate variability and is most likely related to anthropogenic activity in the form of enhanced greenhouse gases. From our investigation we conclude that the delayed warming over much of the Southern Hemisphere may be, in addition to other factors, a consequence of underpinning by natural climate variability. Further bipolar comparison of proxy records of atmospheric circulation demonstrates that change in atmospheric circulation in the Southern Hemisphere led by 400 years, the most abrupt change in Northern Hemisphere atmospheric circulation of the last 9000 years. This finding may be highly relevant to understanding a future when warming becomes more fully established in the Southern Hemisphere.

scholarly journals Antarctic interglacial climate variability and implications for changes in ice sheet topography

PAGES news ◽  
2013 ◽  
Vol 21 (1) ◽  
pp. 18-19
Author(s):  
Valérie Masson-Delmotte ◽  
E Capron ◽  
H Goosse ◽  
K Pol ◽  
M Siddal ◽  
...  
Keyword(s):  
Climate Variability ◽  
Ice Sheet ◽  
Ice Sheet Topography

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.

scholarly journals First results of low frequency electromagnetic wave detector of TC-2/Double Star program

2005 ◽  
Vol 23 (8) ◽  
pp. 2803-2811 ◽  
Author(s):  
J. B. Cao ◽  
Z. X. Liu ◽  
J. Y. Yang ◽  
C. X. Yian ◽  
Z. G. Wang ◽  
...  
Keyword(s):  
Electromagnetic Wave ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Geomagnetic Storms ◽  
Low Frequency ◽  
Wave Detector ◽  
Ion Cyclotron Waves ◽  
Satellite Platform ◽  
Ion Cyclotron ◽  
First Results

Abstract. LFEW is a low frequency electromagnetic wave detector mounted on TC-2, which can measure the magnetic fluctuation of low frequency electromagnetic waves. The frequency range is 8 Hz to 10 kHz. LFEW comprises a boom-mounted, three-axis search coil magnetometer, a preamplifier and an electronics box that houses a Digital Spectrum Analyzer. LFEW was calibrated at Chambon-la-Forêt in France. The ground calibration results show that the performance of LFEW is similar to that of STAFF on TC-1. The first results of LFEW show that it works normally on board, and that the AC magnetic interference of the satellite platform is very small. In the plasmasphere, LFEW observed the ion cyclotron waves. During the geomagnetic storm on 8 November 2004, LFEW observed a wave burst associated with the oxygen ion cyclotron waves. This observation shows that during geomagnetic storms, the oxygen ions are very active in the inner magnetosphere. Outside the plasmasphere, LFEW observed the chorus on 3 November 2004. LFEW also observed the plasmaspheric hiss and mid-latitude hiss both in the Southern Hemisphere and Northern Hemisphere on 8 November 2004. The hiss in the Southern Hemisphere may be the reflected waves of the hiss in the Northern Hemisphere.

scholarly journals Measurement of ice-sheet topography using satellite-radar interferometry

1996 ◽  
Vol 42 (140) ◽  
pp. 10-22 ◽  
Author(s):  
Ian Joughin ◽  
Dale Winebrenner ◽  
Mark Fahnestock ◽  
Ron Kwok ◽  
William Krabill
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Surface Displacement ◽  
Horizontal Resolution ◽  
Radar Interferometry ◽  
Altimeter Data ◽  
Laser Altimeter ◽  
Digital Elevation ◽  
Satellite Radar ◽  
Ice Sheet Topography

AbstractDetailed digital elevation models (DEMs) do not exist for much of the Greenland and Antartic ice sheets. Radar altimetry is at present the primary, in many cases the only, source of topographic data over the ice sheets, but the horizontal resolution of such data is coarse. Satellite-radar interferometry uses the phase difference between pairs of synthetic aperture radar (SAR) images to measure both ice-sheet topography and surface displacement. We have applied this technique using ERS-1 SAR data to make detailed (i.e. 80 m horizontal resolution) maps of surface topography in a 100 km by 300 km strip in West Greenland, extending northward from just above Jakobshavns Isbræ. Comparison with а 76 km long line of airborne laser-altimeter data shows that We have achieved a relative accuracy of 2.5 m along the profile. These observations provide a detailed view of dynamically Supported topography near the margin of an ice sheet. In the final section We compare our estimate of topography with phase contours due to motion, and confirm our earlier analysis concerning vertical ice-sheet motion and complexity in ERS-1 SAR interferograms.

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