Southern Hemisphere Middle Latitudes Research Articles

Springtime Southern Hemisphere Quasi‐Stationary Planetary Wave Activities Associated With ENSO/IOD

AbstractThe tropical climate variabilities, such as Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO), are accompanied by changes in the tropical deep convection which can influence the atmospheric circulation in the Southern Hemisphere (SH). To investigate each role of IOD and ENSO in the September‐November (SON) circulation, we examine teleconnection patterns associated with IOD and ENSO events using the ERA5 monthly averaged data from 1979 to 2020. Our approach is to calculate the power spectral density (PSD) of the sea level pressure (SLP) and meridional wind and geopotential height at 300 hPa that are decomposed by zonal wave numbers (ZWNs), and to compute their correlations with IOD and ENSO at each latitudinal band. The main results are that IOD (ENSO) is negatively (positively) correlated with PSDs of ZWN2 and ZWN3 (ZWN1) at 300 hPa in the SH middle latitudes. Considering the Rossby wave train, IOD (ENSO) considerably affects the variability of the ZWN3 (ZWN1) pattern, which influences the meridional exchange of momentum. Additionally, the relationship between IOD and ZWN3 has become tighter in recent years, which is not seen in that with ENSO. The IOD and ENSO events also modify the SLP patterns and meridional surface winds, modulating the sea ice extent in the Southern Ocean. During the highly positive 2019 IOD event, the variability of the middle latitudes atmospheric circulation was considerably larger than climatology, suggesting a higher chance of more extreme weather patterns associated with more frequent intense IOD events in the warming climate.

A 10Be chronology of the Esmark Moraine and Lysefjorden region, southwestern Norway: Evidence for coeval glacier resurgence in both polar hemispheres during the Antarctic Cold Reversal

From 10Be surface-exposure dating we make the case that classic late-glacial moraines in southwestern Norway, including the iconic Esmark moraine, and in the Southern Hemisphere middle latitudes, including the iconic Birch Hill moraine of the Southern Alps of New Zealand, were constructed coevally within dating uncertainties. This finding of simultaneous glacier resurgence in the two polar hemispheres carries the implication that the millennial-scale climate reversal of the last deglaciation was global and required a change in the energy budget of the earth's climate system.

Cloud and Surface Albedo Feedbacks Reshape 21st Century Warming in Successive Generations of An Earth System Model

AbstractThe relative importance of radiative feedbacks and emissions scenarios in controlling surface warming patterns is challenging to quantify across model generations. We analyze three variants of the Community Earth System Model (CESM) with differing equilibrium climate sensitivities under identical CMIP5 historical and high‐emissions scenarios. CESM1, our base model, exhibits Arctic‐amplified warming with the least warming in the Southern Hemisphere middle latitudes. A variant of CESM1 with enhanced extratropical shortwave cloud feedbacks shows slightly increased late‐21st century warming at all latitudes. In the next‐generation model, CESM2, global‐mean warming is also slightly greater, but the warming is zonally redistributed in a pattern mirroring cloud and surface albedo feedbacks. However, if the nominally equivalent CMIP6 scenario is applied to CESM2, the redistributed warming pattern is preserved, but global‐mean warming is significantly greater. These results demonstrate how model structural differences and scenario differences combine to produce differences in climate projections across model generations.

Patagonian and southern South Atlantic view of Holocene climate

We present a comprehensive 10Be chronology for Holocene moraines in the Lago Argentino basin, on the east side of the South Patagonian Icefield. We focus on three different areas, where prior studies show ample glacier moraine records exist because they were formed by outlet glaciers sensitive to climate change. The 10Be dated records are from the Lago Pearson, Herminita Península-Brazo Upsala, and Lago Frías areas, which span a distance of almost 100 km adjacent to the modern Icefield. New 10Be ages show that expanded glaciers and moraine building events occurred at least at 6120 ± 390 (n = 13), 4450 ± 220 (n = 7), 1450 or 1410 ± 110 (n = 18), 360 ± 30 (n = 5), and 240 ± 20 (n = 8) years ago. Furthermore, other less well-dated glacier expansions of the Upsala Glacier occurred between ~1400 and ∼1000 and ∼2300 and ∼2000 years ago. The most extensive glaciers occurred over the interval from ∼6100 to ∼4500 years ago, and their margins over the last ∼600 years were well within and lower than those in the middle Holocene. The 10Be ages agree with 14C-limiting data for the glacier histories in this area.We then link southern South American, adjacent South Atlantic, and other Southern Hemisphere records to elucidate broader regional patterns of climate and their possible causes. In the early Holocene, a far southward position of the westerly winds fostered warmth, small Patagonian glaciers, and reduced sea ice coverage over the South Atlantic. Although we infer a pronounced southward displacement of the westerlies during the early Holocene, these conditions did not occur throughout the southern mid-high latitudes, an important exception being over the southwest Pacific sector. Subsequently, a northward locus and/or expansion of the winds over the Patagonia-South Atlantic sector promoted the largest glaciers between ∼6100 and ∼4500 years ago and greatest sea ice coverage. Over the last few millennia, the South Patagonian Icefield has experienced successive century-scale advances superimposed on a long-term net decrease in size. Our findings indicate that glaciers and sea ice in the Patagonian-South Atlantic sector of the Southern Hemisphere did not achieve their largest Holocene extents over the last millennium. We conclude that a pattern of more extensive Holocene ice prior to the last millennium is characteristic of the Southern Hemisphere middle latitudes, which differs from the glacier history traditionally thought for the Northern Hemisphere.

Cross-Seasonal Influence of the December–February Southern Hemisphere Annular Mode on March–May Meridional Circulation and Precipitation

Abstract New evidence suggests that interannual variability in zonal-mean meridional circulation and precipitation can be partially attributed to the Southern Hemisphere annular mode (SAM), the dominant mode of climate variability in the Southern Hemisphere (SH) extratropics. A cross-seasonal correlation exists between the December–February (DJF) SAM and March–May (MAM) zonal-mean meridional circulation and precipitation. This correlation is not confined to the SH: it also extends to the Northern Hemisphere (NH) subtropics. When the preceding DJF SAM is positive, counterclockwise, and clockwise meridional cells, accompanied by less and more precipitation, occur alternately between the SH middle latitudes and NH subtropics in MAM. In particular, less precipitation occurs in the SH middle latitudes, the SH tropics, and the NH subtropics, but more precipitation occurs in the SH subtropics and the NH tropics. A framework is built to explain the cross-seasonal impact of SAM-related SST anomalies. Evidence indicates that the DJF SAM tends to lead to dipolelike SST anomalies in the SH extratropics, which are referred to in this study as the SH ocean dipole (SOD). The DJF SOD can persist until the following MAM when it begins to modulate MAM meridional circulation and large-scale precipitation. Atmospheric general circulation model simulations further verify that MAM meridional circulation between the SH middle latitudes and the northern subtropics responds to the MAM SOD.

How did the hydrologic cycle respond to the two-phase mystery interval?

Lake Estancia's transition from a Big Dry episode during the first half of the Mystery Interval to a Big Wet episode during the second half has equivalents in records from across the planet. At the time of this transition, Chinese monsoons experienced pronounced weakening, closed-basin lakes in both the Great Basin of the western United States and in the southern Altiplano of South America underwent a major expansion, mountain glaciers in Southern Hemisphere middle latitudes had retreated, and the rates of increase of CO2 and of δ18O in Antarctic ice underwent a decrease. Finally, the precipitous drop in dust rain over Antarctica and the Southern Ocean terminated as did a similar drop in the 13C to 12C ratio in atmospheric CO2. These changes are consistent with a southward shift of the thermal equator. The cause of such a shift is thought to be an expansion of sea ice caused by a shutdown in deep water production in the northern Atlantic. This creates a dilemma because a similar southward shift is an expected consequence of the Heinrich event #1 which initiated the Mystery Interval.

Missing Stratospheric Ozone Decrease at Southern Hemisphere Middle Latitudes after Mt. Pinatubo: A Dynamical Perspective

Abstract Although large total ozone decreases occurred in the Northern Hemisphere extratropics in the years after the volcanic eruption of Mt. Pinatubo that are generally attributed to the eruption, comparable decreases did not emerge in the Southern Hemisphere. To study this missing decrease, a multiple linear regression was applied to the Chemical and Dynamical Influences on Decadal Ozone Change (CANDIDOZ) Assimilated Three-Dimensional Ozone (CATO) dataset including the solar cycle, the quasi-biennial oscillation (QBO), the effect of volcanic eruptions, the lower stratospheric (LS) Eliassen–Palm (EP) flux to describe the Brewer–Dobson circulation, and stratospheric chlorine increase as explanatory variables. Volcanically induced chemical ozone depletion was overcompensated by the QBO and by a pronounced EP flux anomaly. Using NCEP–NCAR reanalysis data, it is found that the anomalous EP flux was caused by several significant stratospheric wave events (SWEs) from September–November 1991 through 1992 that, together with aerosol heating, led to a significantly enhanced Brewer–Dobson circulation and more ozone transport from the tropics to the extratropics. The onset of the volcanic ozone loss was shifted into 1992 and the strength of the signal was reduced. Most SWEs can be traced back to the troposphere and a significant fraction was associated with atmospheric blocking patterns preceding the SWEs. In 1991/92, the southern annular mode was in a negative phase and El Niño–Southern Oscillation in a warm phase. It is suggested that this constellation favored a flow preconditioning toward quasi-stationary features including blocking, which was significantly enhanced in 1991/92. During June–August 1992, blocking occurred preferably over the southeastern Pacific, pointing to a major ENSO influence on LS wave activity.

Assessment of the breakup of the Antarctic polar vortex in two new chemistry‐climate models

Successful simulation of the breakup of the Antarctic polar vortex depends on the representation of tropospheric stationary waves at Southern Hemisphere middle latitudes. This paper assesses the vortex breakup in two new chemistry‐climate models (CCMs). The stratospheric version of the UK Chemistry and Aerosols model is able to reproduce the observed timing of the vortex breakup. Version 2 of the Goddard Earth Observing System (GEOS V2) model is typical of CCMs in that the Antarctic polar vortex breaks up too late; at 10 hPa, the mean transition to easterlies at 60°S is delayed by 12–13 days as compared with the ERA‐40 and National Centers for Environmental Prediction reanalyses. The two models' skill in simulating planetary wave driving during the October–November period accounts for differences in their simulation of the vortex breakup, with GEOS V2 unable to simulate the magnitude and tilt of geopotential height anomalies in the troposphere and thus underestimating the wave driving. In the GEOS V2 CCM the delayed breakup of the Antarctic vortex biases polar temperatures and trace gas distributions in the upper stratosphere in November and December.

Observed relationships between the Southern Annular Mode and atmospheric carbon dioxide

The authors examine the observed relationships between large‐scale climate variability and concentrations of atmospheric carbon dioxide (CO2) in the Southern Hemisphere. The results reveal that month‐to‐month variations in the rate of change of atmospheric CO2 at Palmer Station on the Antarctic Peninsula are significantly related to fluctuations in the dominant mode of Southern Hemisphere atmospheric variability, the so‐called Southern Annular Mode (SAM). A similar but weaker relationship between the SAM and atmospheric CO2 is evident at Syowa Station in eastern Antarctica, but not at the South Pole or stations located in Southern Hemisphere middle latitudes. Hence the SAM is most clearly related to fluctuations in atmospheric CO2 at locations that sample the westerly flow over the high latitudes of the Southern Ocean. Results based on CO2 flux estimates from the Atmospheric Tracer Transport Model Intercomparison Project (TransCom) suggest the observed relationships at least partially reflect the impact of the SAM on the flux of CO2 over the Southern Ocean.

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A model study of total ozone evolution 1979–2000 — the role of individual natural and anthropogenic effects

The SUNY‐SPB 2‐D model is used to model ozone behavior during the period 1970–2000. The roles of different natural and human‐induced impacts (solar variability, volcanoes, changes in dynamics, increasing chlorine and bromine concentrations) on the column ozone are studied separately as well as in combination. We found that variations in solar UV radiation produce global total ozone fluctuations that are comparable to those due to volcanic eruptions and increasing concentrations of chlorine and bromine during this period. We also suggest that the physical reason for the different observed time behavior of total ozone in the Northern and Southern Hemisphere middle latitudes during the 1990s may be found in the greater importance of mixing of polar processed air into middle latitudes in the Southern hemisphere.

Interhemispheric linkage of paleoclimate during the last glaciation

Combined glacial geologic and palynologic data from the southern Lake District, Seno Reloncaví, and Isla Grande de Chiloé in middle latitudes (40°35’–42°25’S) of the Southern Hemisphere Andes suggest (1) that full‐glacial or near‐full‐glacial climate conditions persisted from about 29,400 to 14,550 14C yr BP in late Llanquihue time, (2) that within this late Llanquihue interval mean summer temperature was depressed 6°–8°C compared to modern values during major glacier advances into the outer moraine belt at 29,400, 26,760, 22,295–22,570, and 14,550–14,805 14C yr BP, (3) that summer temperature depression was as great during early Llanquihue as during late Llanquihue time, (4) that climate deteriorated from warmer conditions during the early part to colder conditions during the later part of middle Llanquihue time, (5) that superimposed on long‐term climate deterioration are Gramineae peaks on Isla Grande de Chiloé that represent cooling at 44,520–47,110 14C yr BP (T‐11), 32,105–35,764 14C yr BP (T‐9), 24,895–26,019 14C yr BP (T‐7), 21,430–22,774 14C yr BP (T‐5), and 13,040–15,200 14C yr BP (T‐3), (6) that the initial phase of the glacial/interglacial transition of the last termination involved at least two major steps, one beginning at 14,600 14C yr BP and another at 12,700–13,000 14 C yr BP, and (7) that a late‐glacial climate reversal of ≥2–3° C set in close to 12,200 14C yr BP, after an interval of near‐interglacial warmth, and continued into Younger Dryas time. The late‐glacial climate signal from the southern Chilean Lake District ties into that from proglacial Lago Mascardi in the nearby Argentine Andes, which shows rapid ice recession peaking at 12,400 14C yr BP, followed by a reversal of trend that culminated in Younger‐Dryas‐age glacier readvance at 11,400–10,200 14C yr BP.Many full‐ and late‐glacial climate shifts in the southern Lake District match those from New Zealand at nearly the same Southern Hemisphere middle latitudes. At the last glacial maximum (LGM), snowline lowering relative to present‐day values was nearly the same in the Southern Alps (875 m) and the Chilean Andes (1000 m). Particularly noteworthy are the new Younger‐Dryas‐age exposure dates of the Lake Misery moraines in Arthur's Pass in the Southern Alps. Moreover, pollen records from the Waikato lowlands on North Island show that a major vegetation shift at close to 14,700 14C yr BP marked the beginning of the last glacial/interglacial transition (Newnham et al. 1989).The synchronous and nearly uniform lowering of snowlines in Southern Hemisphere middle‐latitude mountains compared with Northern Hemisphere values suggests global cooling of about the same magnitude in both hemispheres at the LGM. When compared with paleoclimate records from the North Atlantic region, the middle‐latitude Southern Hemisphere terrestrial data imply interhemispheric symmetry of the structure and timing of the last glacial/interglacial transition. In both regions atmospheric warming pulses are implicated near the beginning of Oldest Dryas time (∼14,600 14C yr BP) and near the Oldest Dryas/Bölling transition (∼12,700–13,000 14 C yr BP). The second of these warming pulses was coincident with resumption of North Atlantic thermohaline circulation similar to that of the modern mode, with strong formation of Lower North Atlantic Deep Water in the Nordic Seas. In both regions, the maximum Bölling‐age warmth was achieved at 12,200–12,500 14 C yr BP, and was followed by a reversal in climate trend. In the North Atlantic region, and possibly in middle latitudes of the Southern Hemisphere, this reversal culminated in a Younger‐Dryas‐age cold pulse.Although changes in ocean circulation can redistribute heat between the hemispheres, they cannot alone account either for the synchronous planetary cooling of the LGM or for the synchronous interhemispheric warming steps of the abrupt glacial‐to‐interglacial transition. Instead, the dominant interhemispheric climate linkage must feature a global atmospheric signal. The most likely source of this signal is a change in the greenhouse content of the atmosphere. We speculate that the Oldest Dryas warming pulse originated from an increase in atmospheric water‐vapor production by half‐precession forcing in the tropics. The major thermohaline switch near the Oldest Dryas/Bölling transition then couldhave triggered another increase in tropical water‐vapor production to near‐interglacial values.

Ozone production and transports in the tropical Atlantic region during the biomass burning season

Tropospheric O3 distributions over the Atlantic Ocean have been calculated with a coupled chemistry‐general circulation model. Photochemically produced O3, mainly from biomass burning emissions, dominates O3 abundances over the tropical Atlantic Ocean in the southern hemisphere (SH) during September/October. On the other hand, O3 of stratospheric origin strongly contributes to the tropospheric O3 column at latitudes poleward of 30°S. Simulated tropospheric flow patterns are in good agreement with European Centre for Medium‐Range Weather Forecasts analyses and trajectory studies. Tracer transports over the tropical South Atlantic Ocean are strongly influenced by wind shear between the boundary layer and the free troposphere, leading to a stratification of O3. At the surface relatively O3‐poor air is transported from SH middle latitudes. At higher altitudes, relatively O3‐rich air is transported from the African biomass burning regions between 2 and 5 km and from South American biomass burning regions in the mid‐to‐upper troposphere. The model simulates O3 production rates of 10–50 parts per billion by volume (ppbv) O3 d−1 in the lower troposphere over the biomass burning regions and 2–6 ppbv O3 d−1 in the middle and upper troposphere. Photochemical destruction of O3 prevails in the lower troposphere over the ocean, maximizing in the African and South American outflow regions. In the northern hemisphere, in situ photochemically produced O3 dominates throughout most of the troposphere. Calculated O3 volume mixing ratios are compared with a latitude‐altitude O3 distribution measured during an Atlantic ship cruise along 30°W, between 55°N and 30°S, in September/October 1988, and with ozone sonde measurements from Southern African Fire Atmospheric Research Initiative/Transport and Atmospheric Chemistry Near the Equator—Atlantic (SAFARI/TRACE A) in September/October 1992. Calculated O3 levels agree reasonably well with the ship cruise data, except for the tropical SH lower troposphere where the model significantly underestimates O3. However, modeled vertical O3 distributions are underpredicted compared to TRACE A sonde measurements. Simulated O3 columns over the ocean are somewhat lower compared to values retrieved from satellite data, in particular over the tropical Atlantic. The underestimation is probably due to the neglect of higher hydrocarbon chemistry in the model.

Concentration variations of atmospheric CO<sub>2</sub> over Syowa Station, Antarctica and their interpretation

Aircraft and ground-based measurements of the atmospheric CO 2 concentration have been made at Syowa Station, Antarctica since January 1983. The minimum concentration of the average seasonal CO 2 cycle occurs in March throughout the troposphere, while the maximum concentration appears in mid-August in the upper troposphere and in late September in the lower and middle troposphere. The peak-to-peak amplitude of the cycle decreases slightly with height. The CO 2 concentration increases with height during most of the year, but from late winter to spring this height dependency is minimal. To examine the contribution of the atmospheric transport processes to these variations of the CO 2 concentration, a 3-dimensional trajectory analysis was performed using data from the US National Meteorological Center. From the results obtained, it is postulated that northern hemispheric air with relatively high CO 2 concentration is transported to the antarctic region through the upper troposphere from late fall to winter, while air with low CO 2 concentration is transported from the southern hemisphere middle latitudes into the antarctic region through the lower troposphere in the remaining seasons. It is hypothesized that these air transport processes could influence CO 2 variations over the station. DOI: 10.1034/j.1600-0889.47.issue4.1.x

Palaeomagnetism of New Zealand glacigenic deposits

The late Cenozoic record of glaciation of the Southern Alps is one of the most detailed in the Southern Hemisphere. Despite attempts to improve the resolution of the terrestrial record, recent research has confirmed the presence of a gap in the terrestrial record of glaciation between 2.1 Ma and 0.35 Ma which has been attributed to the combined effects of rapid uplift and erosion (Suggate 1991). In contrast, evidence from South America and Tasmania suggest that glaciers were most extensive in the Southern Hemisphere middle latitudes at about 1 Ma (Clapperton, 1991; Fitzsimons and Colhoun, 1991; Fitzsimons et al., 1993). In these two locations palaeomagnetic studies have proven to be a useful means of identifying Early Pleistocene deposits on the basis of polarity of glaciolacu-strine sediments. Research on similar problems in Tasmania (Pollington et al., 1993) stimulated a pilot project that was designed to test the existing New Zealand stratigraphic model by examining the polarity of glaciolacustrine sediments.

The Use of Available Potential Energy to Evaluate the Impact of Satellite Data on Numerical Model Analysis during FGGE

Available potential energy (APE) calculations are used to evaluate the influence of the FGGE satellite observing system during the first Special Observing Period (SOP-1). Two datasets consisting of the Goddard Laboratory for Atmospheres analyses are used: the complete FGGE IIIb set which has incorporated satellite soundings and a NOSAT set which incorporates only conventional data. The major portion of the study uses the exact (isentropic) formulation of APE; however, some introductory comparisons are made with the approximate (isobaric) form. Time series of the daily total APE values show the NOSAT set yielding slightly larger values in both APE formulations, with the approximate form zonal component exhibiting the largest difference, An examination of the average eddy APE (exact form) contributions from 4° latitude rings reveals that in the Southern Hemisphere middle latitudes the NOSAT values are larger than the FFGE values; however in the Northern Hemisphere the differences are negligible. Analyses of the vertically integrated gridpoint contributions to the eddy APE reveal that the exact form of the APE clearly defines cyclone scale features. The gridpoint distributions show only minor differences between the Northern Hemisphere FGGE and NOSAT analyses, but substantial differences exist in the Southern Hemisphere where the satellite soundings apparently add detail to the FGGE set by locating the trough and ridge systems associated with cyclones more accurately. However, the weaker thermal gradients obtained from satellite soundings tend to yield smaller eddy APE values. Temporal standard deviations of the gridpoint contributions to the eddy APE are closely related to extratropical cyclone tracks. Again there is essentially no difference in the two datasets in the Northern Hemisphere, but differences exist in the Southern Hemisphere. Finally an analysis of the FGGE-NOSAT temperature differences in vertical cross sections along 54°N and 54°S show larger differences in the Southern Hemisphere. Some of the differences clearly propagate eastward during a three-day period. In some areas large differences of one sign overlay large differences of the opposite sign implying significant differences in static stability between the two sets.

北半球夏季モンスーン時における雲量変動の解析

The broad-scale fluctuations of cloudiness over the Eastern Hemisphere during the northern summer monsoon were investigated by using daily satellite mosaic pictures taken from June 1 to September 30, 1973. Spectral analysis revealed two dominant periodicities, of around 40 days and around 15 days. Cross-spectral, time-sectional, time-lag correlation and phase-lag vector analysis were applied to reveal the characteristics of these two modes in the time-space field. The fluctuation of 40-day period shows marked northward movement of cloudiness from the equatorial zone to the mid-latitudes (around 30 * E) over the whole Asian monsoon area, and southward movement over Africa and the central Pacific. The northward movement is most apparent over the India-Indian Ocean sector. The fluctuation of this mode is associated with the major active-break cycle of the monsoon over the whole Asian monsoon area. The fluctuation of 15-day period shows similar features to that of 40-day period, but includes two clockwise rotations, one over India and Southeast Asia and the other over the western Pacific. A southward movement from the equatorial zone to the Southern Hemisphere middle latitudes is also prominent to the east and west of Australia. The fluctuation of this mode seems to correspond with the movements of equatorial, monsoon (or tropical), and westerly disturbances. It is also suggested that the fluctuation of 40-day period may be closely connected with the global-scale zonal oscillation in the equatorial zone and that of 15-day period may exist as a result of meridional wave interactions.

The vertical distribution of atmospheric ozone over Christchurch, New Zealand

AbstractThe results of a limited series of ozone‐sonde ascents made at Christchurch, New Zealand (latitude 43.5°S) during 1965‐66 with Brewer‐Mast electro‐chemical sondes are discussed. It is found that the vertical distribution of ozone and the pattern of its seasonal variation is similar to that found at Aspendale (southeastern Australia, latitude 38.0°S), but that the Christchurch ozone concentrations are greater at all atmospheric levels. It is further shown that at Christchurch the horizontal transport of ozone by transient eddies is southward at all levels and that the annual average vertically integrated flux is not very different from that observed at a comparable latitude in the Northern Hemisphere. Consideration of the middle latitude ozone budget tends to indicate a coefficient of vertical eddy diffusion in the lower stratosphere of the order of 105 cm2 s−1 for the Southern Hemisphere middle latitudes. Major assumptions involved in this estimate are pointed out.