Antarctic Air Temperature Research Articles

Future Antarctic Climate: Storylines of Midlatitude Jet Strengthening and Shift Emergent from CMIP6

Abstract A main source of regional climate change uncertainty is the large disparity across models in simulating the atmospheric circulation response to global warming. Using the latest suite of global climate models from the sixth phase of the Coupled Model Intercomparison Project (CMIP6), a storyline approach is adopted to derive physically plausible scenarios of Antarctic climate change for 2070–99, according to Shared Socioeconomic Pathway SSP5-8.5. These storylines correspond to differences in the simulated amount of seasonal sea ice loss and either (i) the delay in the summertime stratospheric polar vortex (SPV) breakdown or (ii) wintertime SPV strengthening, which together constitute robust drivers of the response pattern to future climate change. Such changes combined are known to exert a strong control over the Southern Hemisphere midlatitude jet stream, which we quantify as collectively explaining up to 70% of the variance in jet response in summer and 35% in winter. For summer, the expected strengthening and displacement of the tropospheric jet stream varies between a ∼1 and 2 m s−1 increase and ∼2°–4° poleward shift, respectively, across storylines. In both seasons, a larger strengthening of the jet is correlated with less Antarctic warming. By contrast, the response in precipitation is more consistent but still strongly attenuated by large-scale dynamics. We find that an increase in high-latitude precipitation around Antarctica is more pronounced for storylines characterized by a greater poleward jet shift, particularly in summer. Our results highlight the usefulness of the storyline approach in illustrating model uncertainty and understanding the processes that determine the spread in projected Antarctic regional climate response. Significance Statement Uncertainty in future climate predictions for the Antarctic is dominated by the unknown response of the large-scale (global) atmospheric circulation. In characterizing such uncertainty, plausible outcomes of climate response (storylines) are generated from the organization of model projections according to the amount of simulated seasonal sea ice loss and the delay in summertime breakdown/winter strengthening of the stratospheric westerly circulation (polar vortex). The intensity and location of the tropospheric jet stream is strongly dependent on both factors, which strongly influences the near-surface climate response over Antarctica. We find that the simulated amount that Antarctic air temperatures increase by in the future (to the end of the century) is intrinsically related to the projected intensification of the Southern Hemisphere tropospheric jet, varying by a factor of 2 or more across storylines for summer. Storylines with greater jet strengthening are associated with less Antarctic warming (reduced poleward advection of air masses from lower latitudes). Similar differences are found for changes in jet position, which we note has a much stronger control on mid- to high-latitude precipitation response. This includes both an enhanced wetting response around Antarctica and drying response farther equatorward, for storylines characterized by a greater poleward jet shift.

Ice-sheet expansion from the Ross Sea into McMurdo Sound, Antarctica, during the last two glaciations

An understanding of Antarctic Ice Sheet (AIS) behavior is important for future sea-level predictions. Here, we examine past ice-sheet history in the McMurdo Sound region of the western Ross Sea over the last two glacial-interglacial cycles in order to gain insight into the drivers of ice-sheet change. Surficial mapping, along with radiocarbon dates of lacustrine algae and uranium-thorium disequilibrium dates of lacustrine carbonates from ice-dammed lakes, allow reconstruction of the timing and origin of grounded ice in McMurdo Sound during the last glacial maximum (LGM) and penultimate glaciation. During the LGM, ice-surface elevation profiles and distribution of erratics indicate ice flow into southern McMurdo Sound from the Ross Sea, rather than seaward expansion of local glaciers from the Royal Society Range. The grounded ice in McMurdo Sound flowed westward to block the mouths of valleys in the Royal Society Range and to dam proglacial lakes. In Marshall Valley, maximum ice extent during what is termed the Ross Sea glaciation, was achieved by 18 ka and remained close to this position until after 14 ka. The pattern of surficial deposits suggests that ice during the penultimate glaciation, locally named the Marshall glaciation, was slightly more extensive than that of the LGM but had a similar Ross Sea origin. Maximum ice extent in Marshall Valley occurred at ∼145–150 ka; the grounded ice may have receded from the valley mouth shortly after 138 ka. Both ice expansions occurred broadly during times of low Antarctic air temperatures, which have been linked to insolation minima. However, the lack of widespread surface melting ablation zones on the AIS indicates that the link between ice expansion and orbital forcing is likely to be indirect and possibly driven through the ocean. Closer examination of the precise timing of the glacial maxima in Marshall Valley shows that the Marshall glaciation occurred synchronously with the penultimate global maximum; ice recession took place during Termination II. In contrast, maximum ice extent during the Ross Sea glaciation along the Royal Society Range occurred after the global LGM, during Termination I. Deglaciation was primarily an early Holocene event. We attribute this delayed maximum and deglaciation (relative to global events) to the effect of rising accumulation on ice-sheet mass balance.

Reliability of Antarctic air temperature changes from Polar WRF: A comparison with observations and MAR outputs

This study investigates the near-surface air temperature changes over the Antarctic Ice Sheet (AIS) since 1979 using the Polar Weather Research and Forecasting model (Polar WRF, version 3.9.1) at a horizontal resolution of 27 km. Its performance is estimated by quality-controlled monthly temperature measurements from 46 automatic and manual weather stations, and the outputs of the Regional Atmosphere Model (Modèle Atmosphérique Régional, MAR) forced by ERA-Interim (MAR-ERAI) and ERA-5 (MAR-ERA5). Although warm mean biases at interior stations and cold mean biases at coastal stations are observed for the annual and seasonal mean temperatures, all simulations exhibit robust consistency with the year-to-year variability in the observed temperatures. Compared to MAR, Polar WRF presents a warmer temperature, especially on the West AIS (WAIS). Moreover, while Polar WRF shows a poorer performance than MAR over the AP (Antarctic Peninsula) with respect to the observations, Polar WRF can generally capture the trends on the East AIS (EAIS) and WAIS and shows smaller mean biases in winter and autumn. For 1979–2018, Polar WRF shows a warming trend east of 60°E in the EAIS and parts of the AP and WAIS and an insignificant cooling trend in other regions for the annual temperature. The MAR simulations agree on the warming trend in most regions of the EAIS and WAIS but show different annual warming trends over the AP and East Antarctic Plateau.

Accelerated Climate Changes in Weddell Sea Region of Antarctica Detected by Extreme Values Theory

On 13 February 2020, The Guardian, followed by many other newspapers and websites, published the news that on 9 February 2020, Antarctic air temperatures rose to about 20.75 ∘C in a base logged at Seymour Island. This value has not yet been validated by the WMO (World Meteorological Organization), but it is not the first time that an extreme temperature was registered in these locations. The recorded temperatures have often been described as “abnormal and anomalous”, according to a statement made by scientists working at the Antarctic bases. Since polar regions have shown the most rapid rates of climate change in recent years, this abnormality is of primary interest in the context of vulnerability of the Antarctic to climate changes. Using data detected at different Antarctic bases, we investigate yearly maxima and minima of recorded temperatures, in order to establish whether they can be considered as usual extreme events or abnormal. We found evidence for disagreement with the extreme values theory, indicating accelerated climate changes in the Antarctic, that is, a local warming rate that is much faster than global averages.

An assessment of recent global atmospheric reanalyses for Antarctic near surface air temperature

The quality-controlled monthly air temperature records from 32 manned stations and 10 automatic weather stations are used to assess the performance of Climate Forecast System Reanalysis (CFSR), the ECMWF “Interim” reanalysis (ERA-Interim), the Japan Meteorological Agency 55-year Reanalysis (JRA-55), the Modern-Era Retrospective Analysis for Research and Applications 2 (MERRA-2), and four twentieth century reanalysis data sets (20CR, ERA-20C, CERA-20C and ERA-20CM). The performance of the datasets for Antarctic air temperature differs on different time scales and with glaciological regime. In general, these datasets have higher mean absolute error (MAE) in the winter months and lower MAE in the summer months. Overall, MERRA-2 presents highest performance for monthly air temperature values, with MAE <2 °C at any month. ERA-Interim best represents the inter-annual variability in monthly air temperature for the 1979–2010 period. In the 20th century datasets, changes in temperature prior to 1979 are more uncertain than variability after 1979. Furthermore, substantial inhomogeneities occur in the 20th century datasets, and as a result, their temperature trends are found to be largely spurious.

Glacial–interglacial interplay of southern- and northern-origin deep waters in the São Paulo Plateau – Vema Channel area of the western South Atlantic

The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the global climate system due to its role in oceanic heat transport, CO2 exchange between the ocean and atmosphere, and carbon storage in the ocean interior. Previous studies have proposed dramatic changes in the global thermohaline circulation during glacial–interglacial cycles. Here, we present isotopic, geochemical and foraminiferal records from the core AI-3152 (water depth 3435 m). These data demonstrate shifts in the depth of northern- and southern-sourced deep water masses, as well as of foraminiferal lysocline in the São Paulo Plateau area, north-westward of the Vema Channel, in the western South Atlantic over the last 167 kyr. That the study area was bathed by southern-origin deep water masses during MIS 6, 4–2 and MIS 5.4–5.1, whereas a prevalence of northern-sourced waters is reconstructed for interglacials and MIS 5.5 and 1. Our data suggest that a carbonate saturation state associated with deep water ventilation, Antarctic air temperatures, ocean–atmosphere gas exchange, Southern Ocean upwelling rates and likely productivity changes significantly affected the deep sea oceanographic conditions in the São Paulo Plateau area during glacials and MIS 5.4–5.1. A comparison of δ18OCw and δ13СCw recorded from core AI-3152 to other stable isotope records from the Rio Grande Rise, to the east of the Vema Channel clearly indicated the presence of a southern-derived analogue of dense Weddell Sea Deep Water at 3.4–4 km depth in the Vema Channel area during the MIS 3–2 interval. An approximately 500 m steeper W-E slope on the boundary of two southern-origin deep water masses was inferred on both sides of the Vema Channel during MIS 3–2. This boundary shift likely reflects a northward expansion of the densest water mass in the Atlantic, thereby impacting geostrophic balance.

CO2 radiative forcing and Intertropical Convergence Zone influences on western Pacific warm pool climate over the past 400 ka

The western Pacific warm pool (WPWP) is an important heat source for the atmospheric circulation and influences climate conditions worldwide. Estimating WPWP sensitivity to past radiative forcing perturbations is important for understanding the magnitudes and patterns of current and projected tropical climate change. Here we present a new Mg/Ca-based sea surface temperature (SST) reconstruction over the past 400ka from the Bismarck Sea, off Papua New Guinea, along with benthic foraminiferal δ18O records and a transient intermediate complexity earth system model simulation. The Mg/Ca-SST record exhibits a close similarity with atmospheric CO2 content for the whole study period. Our model analysis demonstrates that greenhouse gas forcing is the primary driver for glacial/interglacial SST changes in the entire WPWP region. Mg/Ca-SST in the Bismarck Sea also includes a weaker precessional component, which covaries with reconstructed and simulated local precipitation, and simulated surface currents. We propose that orbitally driven latitudinal shifts of the Intertropical Convergence Zone and oceanic heat advection are responsible for this residual SST variability. On glacial timescales the reconstructed WPWP surface temperature changes over the past 400ka are highly correlated with East Antarctic air temperature variations. The strong effect of greenhouse gas forcings on both records and on global mean temperature variability allows us to determine a scaling factor of 1–1.5 between reconstructed WPWP temperature anomalies and estimates of the global mean temperature.

Accelerated thermokarst formation in the McMurdo Dry Valleys, Antarctica

Thermokarst is a land surface lowered and disrupted by melting ground ice. Thermokarst is a major driver of landscape change in the Arctic, but has been considered to be a minor process in Antarctica. Here, we use ground-based and airborne LiDAR coupled with timelapse imaging and meteorological data to show that 1) thermokarst formation has accelerated in Garwood Valley, Antarctica; 2) the rate of thermokarst erosion is presently ~ 10 times the average Holocene rate; and 3) the increased rate of thermokarst formation is driven most strongly by increasing insolation and sediment/albedo feedbacks. This suggests that sediment enhancement of insolation-driven melting may act similarly to expected increases in Antarctic air temperature (presently occurring along the Antarctic Peninsula), and may serve as a leading indicator of imminent landscape change in Antarctica that will generate thermokarst landforms similar to those in Arctic periglacial terrains.

A geochemical and sedimentary record of high southern latitude Holocene climate evolution from Lago Fagnano, Tierra del Fuego

Situated at the southern margin of the hemispheric westerly wind belt and immediately north of the Antarctic Polar Frontal zone, Tierra del Fuego is well-positioned to monitor coupled changes in the ocean–atmosphere system of the high southern latitudes. Here we describe a Holocene paleoclimate record from sediment cores obtained from Lago Fagnano, a large lake in southern Tierra del Fuego at 55°S, to investigate past changes in climate related to these two important features of the global climate system. We use an AMS radiocarbon chronology for the last 8000yr based on pollen concentrates, thereby avoiding contamination from bedrock-derived lignite. Our chronology is consistent with a tephrochronologic age date for deposits from the middle Holocene Volcán Hudson eruption. Combining bulk organic isotopic (δ13C and δ15N) and elemental (C and N) parameters with physical sediment properties allows us to better understand sediment provenance and transport mechanisms and to interpret Holocene climate and tectonic change during the last 8000yr. Co-variability and long-term trends in C/N ratio, carbon accumulation rate, and magnetic susceptibility reflect an overall Holocene increase in the delivery of terrestrial organic and lithogenic material to the deep eastern basin. We attribute this variability to westerly wind-derived precipitation. Increased wind strength and precipitation in the late Holocene drives the Nothofagus forest eastward and enhances run-off and terrigenous inputs to the lake. Superimposed on the long-term trend are a series of abrupt 9 negative departures in C/N ratio, which constrain the presence of seismically-driven mass flow events in the record. We identify an increase in bulk δ13C between 7000 and 5000calyr BP that we attribute to enhanced aquatic productivity driven by warmer summer temperatures. The Lago Fagnano δ13C record shows similarities with Holocene records of sea surface temperature from the mid-latitude Chilean continental shelf and Antarctic air temperatures from the Taylor Dome ice core record in East Antarctica. Mid-Holocene warming occurred simultaneously across the Antarctic Frontal Zone, and in particular, in locations currently influenced by the Antarctic Circumpolar Current.

Deglacial abrupt climate change in the Atlantic Warm Pool: A Gulf of Mexico perspective

[1] During the last deglaciation, Greenland ice core and North Atlantic sediment records exhibit multiple abrupt climate events including the Younger Dryas cold episode (12.9–11.7 ka). However, evidence for the presence of the Younger Dryas in the Gulf of Mexico (GOM) and the relationship between GOM sea surface temperature (SST) and high-latitude climate change is less clear. We present new Mg/Ca-SST records from two varieties of the planktonic foraminifer Globigerinoides ruber (white and pink) to assess northern GOM SST history from approximately 18.4–10.8 ka. Thirty-five accelerator mass spectrometry (AMS) 14C dates from Orca Basin core MD02-2550 provide excellent age control and document high sedimentation rates (∼40 cm/kyr). G. ruber (white and pink) Mg/Ca-SST data exhibit increases (∼4.6 ± 0.6°C and ∼2.2 ± 0.5°C, respectively) from at least 17.8–16.6 ka, with nearly decadal resolution that are early relative to the onset of the Bolling-Allerod interstadial. Moreover, G. ruber (white) SST decreases at 16.0–14.7 ka (∼1.0 ± 0.5°C) and 12.8–11.6 ka (∼2.4 ± 0.6°C) correlate to the Oldest and Younger Dryas in Greenland and Cariaco Basin. The G. ruber (pink) SST record, which reflects differences in seasonality and/or depth habitat, is often not in phase with G. ruber (white) and closely resembles Antarctic air temperature records. Overall, it appears that Orca Basin SST records follow Antarctic air temperature early in the deglacial sequence and exhibit enhanced seasonality during Greenland stadials.

Spatial distribution of 10 m firn temperature in the Antarctic ice sheet

A database of Antarctic 10 m firn temperature was constructed using available borehole temperature measurements with data quality control to extend knowledge of Antarctic climate. Slopes from a high-resolution digital elevation model and the main ice divide were used to delineate main drainage sectors across Antarctica. In each drainage sector, a quantitative relationship between temperature and latitude, longitude and altitude was established using available firn temperature data. Quantitative relationships incorporating other factors affecting Antarctic air temperature such as atmospheric circulation and small-scale topography were used to derive a 10-km resolution grid map of surface temperature. The resulting temperature patterns presented a reasonable depiction of both large and small-scale variations in Antarctic 10 m firn temperature. This map is useful for many spatial variation studies, Antarctic ice sheet models, and comparison with satellite-derived temperature data and outputs of atmospheric general circulation models.

Insolation and sea level variations during Quaternary interglacial periods: A review of recent results with special emphasis on the last interglaciation

During the last million years, interglacial periods were characterized by sea level, Antarctic air temperature and atmospheric CO 2 concentrations different from those of today. The relationship between CO 2 and climate remained rather constant over these intervals, which confirms that CO 2 acts as a positive feedback to insolation forcing. The thermohaline circulation and the Atlantic meridional overturning are sources of another strong positive feedback mechanism. They have been responsible for the partial melting of the West Antarctic Ice Sheet during the last interglaciation and for the amplification of the insolation forcing to trigger the last glacial inception.

Correction to “Twentieth century Antarctic air temperature and snowfall simulations by IPCC climate models”

Correction to “Twentieth century Antarctic air temperature and snowfall simulations by IPCC climate models”

Twentieth century Antarctic air temperature and snowfall simulations by IPCC climate models

We compare new observationally‐based data sets of Antarctic near‐surface air temperature and snowfall accumulation with 20th century simulations from global climate models (GCMs) that support the Intergovernmental Panel on Climate Change Fourth Assessment Report. Annual Antarctic snowfall accumulation trends in the GCMs agree with observations during 1960–1999, and the sensitivity of snowfall accumulation to near‐surface air temperature fluctuations is approximately the same as observed, about 5% K−1. Thus if Antarctic temperatures rise as projected, snowfall increases may partially offset ice sheet mass loss by mitigating an additional 1 mm y−1 of global sea level rise by 2100. However, 20th century (1880–1999) annual Antarctic near‐surface air temperature trends in the GCMs are about 2.5‐to‐5 times larger‐than‐observed, possibly due to the radiative impact of unrealistic increases in water vapor. Resolving the relative contributions of dynamic and radiative forcing on Antarctic temperature variability in GCMs will lead to more robust 21st century projections.

Hemispheric roles of climate forcings during glacial‐interglacial transitions as deduced from the Vostok record and LLN‐2D model experiments

The Vostok ice contains fingerprints of atmospheric greenhouse trace gases, Antarctic temperature, Northern Hemisphere temperature, and global ice volume/sea level changes during the last glacial‐interglacial cycles and thus allows us to investigate the sequences of these climatic events, in particular during the transitions from full glacial to interglacial conditions. The use of the updated CO2 record presented here and a reexamination of the sea level proxy confirm that the succession of changes has been similar through each of the four marked transitions found at Vostok. Antarctic air temperature and CO2 increase in parallel and almost synchronously, while the rapid warmings over Greenland take place during the last half of their change and coincide with the marked decay in continental ice volume. The Vostok results thus emphasize a fundamental difference between South and North in terms of climate dynamics. Our results confirm the role of CO2 as an important amplifier of the glacial‐interglacial warming in the South. It appears also that the marked warming observed at high northern latitudes (lagging behind the CO2 increase by several thousand years) is roughly synchronous with the decay of the northern ice sheets, suggesting a major role of climatic feedback due to this decay. Such a climatic scenario is supported by sensitivity experiments performed with the LLN 2‐D model forced by the Northern Hemisphere insolation and CO2. Model results indicate that the decay of the northern ice sheets and the Northern Hemisphere temperature depend primarily on the northern summer insolation. These results, nevertheless, could be affected if mechanisms specific to the Southern Hemisphere appear to play a major role in driving the Northern Hemisphere climate. The model also helps to constrain the time response of ice volume to insolation and CO2 changes.

Climate impact of late quaternary equatorial pacific sea surface temperature variations

Magnesium/calcium data from planktonic foraminifera in equatorial Pacific sediment cores demonstrate that tropical Pacific sea surface temperatures (SSTs) were 2.8 degrees +/- 0.7 degrees C colder than the present at the last glacial maximum. Glacial-interglacial temperature differences as great as 5 degrees C are observed over the last 450 thousand years. Changes in SST coincide with changes in Antarctic air temperature and precede changes in continental ice volume by about 3 thousand years, suggesting that tropical cooling played a major role in driving ice-age climate. Comparison of SST estimates from eastern and western sites indicates that the equatorial Pacific zonal SST gradient was similar or somewhat larger during glacial episodes. Extraction of a salinity proxy from the magnesium/calcium and oxygen isotope data indicates that transport of water vapor into the western Pacific was enhanced during glacial episodes.

The influence of Antarctic sea ice on glacial-interglacial CO2 variations

Ice-core measurements indicate that atmospheric CO2 concentrations during glacial periods were consistently about 80 parts per million lower than during interglacial periods. Previous explanations for this observation have typically had difficulty accounting for either the estimated glacial O2 concentrations in the deep sea, 13C/12C ratios in Antarctic surface waters, or the depth of calcite saturation; also lacking is an explanation for the strong link between atmospheric CO2 and Antarctic air temperature. There is growing evidence that the amount of deep water upwelling at low latitudes is significantly overestimated in most ocean general circulation models and simpler box models previously used to investigate this problem. Here we use a box model with deep-water upwelling confined to south of 55 degrees S to investigate the glacial-interglacial linkages between Antarctic air temperature and atmospheric CO2 variations. We suggest that low glacial atmospheric CO2 levels might result from reduced deep-water ventilation associated with either year-round Antarctic sea-ice coverage, or wintertime coverage combined with ice-induced stratification during the summer. The model presented here reproduces 67 parts per million of the observed glacial-interglacial CO2 difference, as a result of reduced air-sea gas exchange in the Antarctic region, and is generally consistent with the additional observational constraints.

A comparison of the Vostok ice deuterium record and series from Southern Ocean core MD 88-770 over the last two glacial-interglacial cycles

Taking advantage of the fact that the Vostok deuterium (δD) record now covers almost two entire climatic cycles, we have applied the orbital tuning approach to derive an age-depth relation for the Vostok ice core, which is consistent with the SPECMAP marine time scale. A second age-depth relation for Vostok was obtained by correlating the ice isotope content with estimates of sea surface temperature from Southern Ocean core MD 88-770. Both methods lead to a close correspondence between Vostok and MD 88-770 time series. However, the coherence between the correlated δD and insolation is much lower than between the orbitally tuned 8D and insolation. This reflects the lower accuracy of the correlation method with respect to direct orbital tuning. We compared the ice and marine records, set in a common temporal framework, in the time and frequency domains. Our results indicate that changes in the Antarctic air temperature quite clearly lead variations in global ice volume in the obliquity and precession frequency bands. Moreover, the average phase we estimated between the filtered δD and insolation signals at precessional frequencies indicates that variations in the southern high latitude surface temperature could be induced by changes in insolation taking place during a large period of the summer in northern low latitudes or winter in southern low latitudes. The relatively large lag found between Vostok δD variations and obliquity-driven changes in insolation suggests that variations in the local radiative balance are not the only mechanism responsible for the variability in surface temperature at those frequencies. Finally, in contrast to the cross-spectral analysis method used in previous studies, the method we use here to estimate the phases can reveal errors in cross-correlations with orbitally tuned chronologies.

Antarctic Temperatures over the Present Century—A Study of the Early Expedition Record

Abstract Air temperature records for 26 expeditions to Antarctica that have overwintered, for periods of at least 9 months, between 1898 and 1958 have been assembled. Using a map of 1957–75 average annual temperature over Antarctica, the results for the expedition sites were made compatible with modern data. The expedition records are unfortunately confined mainly to two regions, the Antarctic Peninsula and the Ross Sea sectors. It is difficult, therefore, to generalize the results to the entire continental area. The expeditions are also somewhat irregularly spaced in time with relatively few occurring in the 1917–34 period. The best guess that can be made is that Antarctic air temperatures now appear to be warmer, by at least 1°C, than those prevailing during the first decade of the twentieth century. The result is broadly consistent with temperature changes that have been reported for both land and marine regions over the rest of the Southern Hemisphere. This result is, however, in contrast with the cou...

Upper Air Temperatures over an Antarctic Station: A preliminary note by

Typical features of antarctic upper air temperature distributions are demonstrated by means of average values and selected ascents. A great seasonal change in the height of the tropopause is pointed out. Attention is drawn to the remarkable agreement between observed stratospheric temperatures in winter and Dobson's estimated values. The causes for the heating of the stratosphere in late winter and spring are discussed. The difference between the tropospheric temperatures in summer between Arctic and Antarctic is assumed to be due to the different value of the surface albedo. Rough estimates indicate that the absorption in the 9.7 μ band by ozone is of great significance to the observed stratospheric temperature contrast between the two polar regions in winter. DOI: 10.1111/j.2153-3490.1955.tb01142.x