Southern Annular Mode Research Articles

ACCESS-CM2-Chem: evaluation of southern hemisphere ozone and its effect on the Southern Annular Mode

Chemistry–climate models are important tools for forecasting the evolution of climate. Of particular importance is the simulation of Antarctic ozone depletion due to its effect on the Southern Annular Mode (SAM). In this paper we evaluate the chemistry–climate model ACCESS-CM2-Chem. We find the simulation of stratospheric ozone by ACCESS-CM2-Chem to be significantly improved relative to its predecessor, and as good as the best of the contemporary chemistry–climate models – the ensemble of which displays considerable variation. We also find that the trend in summertime SAM is simulated well by ACCESS-CM2-Chem compared to the ERA5 reanalysis. Further, we show that this trend is more sensitive to changes in ozone depletion forcing in ACCESS-CM2-Chem than the equivalent model with prescribed ozone. However, a downside of the interactive chemistry of ACCESS-CM2-Chem, relative to the prescribed chemistry version, is an increase in the bias towards later vortex break-ups. Many recent studies have identified the important role of feedbacks between interactive ozone chemistry and climate. This phenomenon will be crucial to understand future projections where the recovery of stratospheric ozone will interact with increasing greenhouse gas driven warming. Based on the performance demonstrated here, ACCESS-CM2-Chem is a promising model with which to further this line of research, although the delay in the vortex break-up induced by the interactive chemistry is an issue that requires further work.

Southern Hemisphere temperature trend in association with greenhouse gases, El Niño Southern Oscillation, and Antarctic Oscillation

In this study, the trend of mean seasonal and annual temperatures of the Southern Hemisphere was calculated based on the HadCRUT5 and NASA-GISS data networks, for the period 1901–2021 and 1951–2021. In order to determine the possible effects on temperature, man, or nature, the relationship with CO2 concentration, GHG (greenhouse gases) radiation exposure, and teleconnections ENSO (El Niño Southern Oscillation) and AAO (Antarctic Oscillation) was examined. The obtained results indicate that there is a significant increasing trend of seasonal and annual temperatures in the Southern Hemisphere, which intensified in the period between 1951 and 2021 (from 0.11 to 0.12 °C per decade). According to climate models, one of the indicators of the dominance of the anthropogenic greenhouse effect is the polar amplification (more intense temperature rise going from the equator to the poles). However, polar amplification was not recorded in the Southern Hemisphere, due to the fact that there was the smallest increase in temperature in the belt between 44°S–64°S. Moreover, in the mentioned zone, the positive trend was smaller in the period between 1951 and 2021 than in the period between 1901 and 2021, which was not to be expected. Nevertheless, the Southern Hemisphere temperature showed a statistically significantly strong correlation with the concentration of CO2observed at the Mauna Loa station. It was also found that there is a significant relationship between the energy impact of greenhouse gases and the Southern Hemisphere temperature, which is logical, because with the growth of GHG, positive radiative forcing increases. When it comes to the impact of telecommunications, both considered teleconnections (ENSO and AAO) have an impact on changes in the temperature of the Southern Hemisphere.

Biases and teleconnections in the Met Office Global Coupled Model version 5.0 (GC5) – insights for seasonal prediction and Australia

The Australian Bureau of Meteorology (The Bureau) has been involved in the package testing and assessment process of the UK Met Office Global Coupled Model Version 5.0 (GC5) configuration. GC5 will underpin the Met Office’s next seasonal prediction system, global coupled numerical weather prediction (NWP) system and Earth System Model. It will also likely be the next version of The Bureau’s seasonal prediction system, and the version to replace the global atmosphere-only NWP system to be the first global coupled NWP system at The Bureau. The GC5 configuration includes a new sea-ice model and substantial updates to almost all areas of model physics. We have evaluated the present-day climate simulation, and compared it to observations and with previous versions GC4 and GC2. Our assessment focuses on the climate mean state and variabilities relevant to Australian seasonal prediction, including the El Niño–Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD), the Southern Annular Mode and the Madden–Julian Oscillation. Notably, in comparison to its predecessor (GC4), GC5 shows significant improvements in the eastern Pacific mean state but a slight degradation in the Indian Ocean in terms of the mean state and variability. These and other results provide us with early insights of the potential performance of the next sub-seasonal or seasonal forecast system. Longstanding issues in the seasonal prediction system associated with the equatorial eastern Indian Ocean biases and an overactive ENSO and IOD will likely remain; however, improvements over the eastern equatorial Pacific in GC5 hold promise of improved prediction skill of ENSO and its teleconnections.

Large‐scale forcing over the homogeneous regions of summer rainfall anomalies in southern Africa

AbstractFor the study region (southern Africa), regional and remote large‐scale climate forcing play vital roles in the seasonal rainfall variability. Thus, uncovering the nature of the relationship between large‐scale circulations and homogeneous regions of rainfall anomalies will enhance the predictability of seasonal rainfall at specific domains in southern Africa. Considering both land and adjacent oceans in southern Africa, six austral summer homogeneous regions of rainfall anomalies were classified using the rotated principal component analysis. The analysis of the physical processes associated with the modulation of the distinct rainfall variability patterns reveals that generally, regional variations in cyclonic/anticyclonic circulations and convergence/divergence in the adjacent oceans (and landmasses) modulate the regional convergence of moisture fluxes in southern Africa. Some classified rainfall variability patterns feature homogeneous landmasses that are contiguous with the adjacent ocean, revealing land and adjacent oceans that respond coherently to the large‐scale circulation anomalies associated with the time development of the rainfall variability pattern. Further, remote climate drivers were found to be distinctively related to the regionalized rainfall anomalies, implying that the respective homogeneous rainfall regions respond differently to the large‐scale forcing induced by the (remote) climate drivers over southern Africa. Specifically, among the climate drivers that influence the hydroclimate of southern Africa, variations in the Southern Annular Mode (SAM) and the El Niño Southern Oscillation are relatively more associated with regionalized summer rainfall anomalies in southern Africa. Above‐average Nino 3.4 index (i.e., El Niño) negatively correlates with regionalized summer rainfall anomalies over large parts of southern Africa. The positive phase of the SAM positively correlates with rainfall anomaly in the homogeneous summer rainfall region comprising the subtropical parts of southern Africa and the homogeneous summer rainfall region comprising the western equatorial parts of the study region.

Relationship between air pollutant distribution and large-scale circulation

The leading mode of the singular value decomposition (SVD) of geopotential height (GPH) and boundary layer structure index (BLSI).

Large-scale and regional climatic influences on surface temperature and precipitation in the South Shetland Islands, northern Antarctic Peninsula.

Using data from SCAR observations, ERA5 reanalysis, and regional climate model simulations (RACMO), we examined the influence of large- and regional-scale climate forcing on temperature and precipitation variations in the South Shetland Islands (SSI). Specifically, we focused on understanding how regional climate indices influence the temporal variability of temperature and precipitation on the SSI. Our findings indicate that both large- and regional-scale climate indices significantly impact the interannual and seasonal temperature variability in the SSI. For instance, the Amundsen Sea Low, characterised by low-pressure systems over the Amundsen Sea, and sea ice extent in the northwestern part of the Weddell Sea, exert a strong influence on temperature variability (r from -0.64 to -0.87; p < 0.05). In contrast, precipitation variability in this region is primarily controlled by regional climatic indices. Particularly, anomalies in atmospheric and surface pressure over the Drake Passage region strongly regulate the interannual variability of precipitation in the SSI (r from -0.46 to -0.70; p < 0.05). Large-scale climatic indices demonstrate low but statistically significant correlations, including the Southern Annular Mode and deep convection in the central tropical Pacific. Given the importance of temperature and precipitation in the glacier changes, we recommend assessing the impact of the Drake region on SSI glaciers.

The impact of local and climate change drivers on the formation, dynamics, and potential recurrence of a massive fish-killing microalgal bloom in Patagonian fjord

Harmful algal blooms (HABs) in southern Chile are a serious threat to public health, tourism, artisanal fisheries, and aquaculture in this region. Ichthyotoxic HAB species have recently become a major annual threat to the Chilean salmon farming industry, due to their severe economic impacts. In early austral autumn 2021, an intense bloom of the raphidophyte Heterosigma akashiwo was detected in Comau Fjord, Chilean Patagonia, resulting in a high mortality of farmed salmon (nearly 6000 tons of biomass) within 15 days. H. akashiwo cells were first detected at the head of the fjord on March 16, 2021 (up to 478 cells mL−1). On March 31, the cell density at the surface had reached a maximum of 2 × 105 cells mL−1, with intense brown spots visible on the water surface. Strong and persistent high-pressure anomalies over the southern tip of South America, consistent with the positive phase of the Southern Annular Mode (SAM), resulted in extremely dry conditions, high solar radiation, and strong southerly winds. A coupling of these features with the high water retention times inside the fjord can explain the spatial-temporal dynamics of this bloom event. Other factors, such as the internal local physical uplift process (favored by the north-to-south orientation of the fjord), salt-fingering events, and the uplift of subantarctic deep-water renewal, likely resulted in the injection of nutrients into the euphotic layer, which in turn could have promoted cell growth and thus high microalgal cell densities, such as reached by the bloom.

Trends and Variability in the Southern Annular Mode over the Common Era

Trends and Variability in the Southern Annular Mode over the Common Era

Intensification of the East Australian Current After ∼1400 CE

AbstractThe East Australian Current (EAC) is the western boundary current of the South Pacific Subtropical Gyre that transports warm tropical waters to higher southern latitudes and significantly impacts the climate of Australia and New Zealand. Modern observations show that the EAC has strengthened with rising global temperatures. However, little is known about the pre‐industrial variability of the EAC and the forcing mechanisms. Planktic foraminifera Globigerinoides ruber (white) Mg/Ca‐based sea surface temperature reconstructions offshore northeastern Australia between 15° and 26°S reveal an increase by ∼1.2°C after ∼1400 CE. We infer that the increase in temperature is related to a stronger EAC heat transport that is likely driven by a strengthening of the Southern Hemisphere subtropical gyre circulation due to a progressive shift of the Southern annular mode toward its positive phase and of El Niño‐Southern Oscillation toward more El Niño‐like conditions.

Intensified modulation of the Pacific north equatorial current bifurcation by the southern annular mode since the early 1990s

Long-term reanalysis data were used to assess inter-decadal to decadal modulations of the North Equatorial Current (NEC) bifurcation in the Pacific after the early 1990s. The wind stress curl anomaly (WSCA) in the region of 10° N-15° N and 160° E-170° E (C-BOX) had been found to excite Rossby waves and control NEC bifurcation along the Philippine coast. Our analysis revealed that the WSCA in the C-BOX has been remotely modulated by the Southern Annular Mode (SAM) since the early 1990s. It is shown that the SAM shifted to its positive phase at this transition and began strongly impacting the WSCA in the C-BOX and the NEC bifurcation. During the positive SAM phase after the early 1990s, strong climate variability occurred in the tropical to subtropical area of the North Pacific, with a clear footprint connected to the Antarctic region. Consistent with that finding, we determined that during the positive SAM phase, a dipole sea surface temperature pattern was generated in the South Pacific; this induced an atmospheric Rossby wave train in upper-level wind shear that propagated northward to the North Pacific. Such effects further enhanced downward motion and divergence at the surface, intensifying the easterlies in the equatorial area and the anticyclonic WSCA in the C-BOX. The anticyclonic WSCA in the C-BOX substantially excited downwelling oceanic Rossby waves at the surface, inducing an equatorward trend of NEC bifurcation after the early 1990s.

Fluctuations of the Universidad Glacier in the Andes of central Chile (34° S) during the latest Holocene derived from a 10Be moraine chronology

The reconstruction of glacier fluctuations during the latest Holocene (<1000 years) is necessary for understanding the climate context preceding the warmer conditions of the 20th and 21st centuries. The glacier records in the Andes of central Chile are suitably located to track former latitudinal changes of the Southern Westerly Winds (SSW), which are mostly unknown at this middle latitude region. Here, we present a reconstruction of the glacial fluctuations using Terrestrial Cosmogenic Nuclides (10Be) dating of boulders resting on moraines and other glacial landforms that make up the moraine complex in the forefield of the Universidad Glacier (34° S). This massive and chaotic-looking moraine was built during the latest Holocene ice advances and subsequent decay of the Universidad Glacier to its present position. Geomorphological mapping and 10Be surface exposure ages (n = 20) show that the Universidad Glacier advanced at least twice to nearly the same maximum extent, first by the 13th to 16th centuries and then by the early to the mid-19th century. Since then, eight moraine ridges denote a rather active and gradual ice demise. We interpret the glacier advances as a response to an equatorward shift of the SWW linked to a long-term negative phase of the Southern Annular Mode (SAM), which embraced net humid and cold atmospheric conditions in central Chile between the 13th century and the mid-19th century. Our glacier chronology is comparable to others from Patagonia and New Zealand, altogether exposing the culmination of the latest Holocene glacial maximum by the mid-19th century, before overall ice decay in a global warming world, with accelerated ice loss since the mid-20th century.

Atmospheric precursors to the Antarctic sea ice record low in February 2022

Antarctic sea ice expansion and recession are asymmetric in nature, with regional and temporal variations. The decade-long overall increase in the Antarctic sea ice extent (SIE) until 2015 showed a decrease in recent years since satellite records were available. The present study focused on determining the atmospheric forcing and climate fluctuations responsible for the lowest SIE record in February 2022. Here, the lowest SIE record was assumed to result from the sea ice recession that began in September 2021. The SIE reached a record low of 2.16 × 106 km2 in February 2022, which was 43% lower than the mean extent of the previous February months since the satellite era. However, the second-lowest SIE was recorded from November 2021 to January 2022. The Weddell Sea, Ross Sea, and Bellingshausen/Amundsen Seas (ABS) sectors experienced the maximum sea ice change on a regional scale. The record-low SIE occurred when the Amundsen Sea Low (ASL) pressure center was intensified, with the Southern Annular Mode (SAM) at its positive phase. Together, these two climate fluctuations played a role in modifying the pressure and wind patterns in Antarctica. The warm northerly winds largely contributed to decreased SIE. Further, the study investigated the Polar Cap Height (PCH), which demonstrates a strengthening of the stratospheric polar vortex and positive polarity of the SAM.

Future trends in atmospheric circulation patterns over Africa south of the equator

Abstract The impact of climate change on the frequency of occurrence of atmospheric circulation patterns can have a wide range of consequences ranging from weather extremes to the modification of pollutant transport. This study uses 11 CMIP6 global climate models (GCMs) to investigate the impact of future climate change on the frequency of occurrence of atmospheric circulation patterns, in Africa south of the equator. Here it is shown from the historical analysis that there are statistically significant trends in the frequency of occurrence of some of the classified circulation types (CTs) in the study region. Further, under the SSP5-8.5 and SSP2-4.5 emission scenarios, the historical CTs were reproduced, suggesting that future climate change will not constrain the existence of the CTs. However, for future emission scenarios, the ensemble of the GCMs projects notable changes in the spatial structure of the CTs and statistically significant trends in the frequency of occurrence of most of the CTs, towards the end of the 21st century. The intensity of the projected changes in the spatial structure and linear trends in the frequency of occurrence of the CTs are relatively stronger under the higher emission scenario. As regards changes in synoptic circulations in the study region, the ensemble of the GCMs project, (i) a positive trend in the frequency of occurrence of austral summer dominant CTs associated with atmospheric blocking of the Southern Hemisphere mid-latitude cyclones, adjacent to South Africa; (ii) alternating frequent periods of enhanced (suppressed) anticyclonic circulation at the western branch of the Mascarene high possibly due to a more positive phase of the Southern Annular Mode (warmer southwest Indian Ocean); (iii) possible weakening of the Angola low. The aforementioned changes can be expected to have direct impacts on the regional climates in the study region.

Spatial and Temporal Trends in the Timing of Budburst for Australian Wine Regions

Background and Aims. This research investigates spatial and temporal trends in budburst timing across Australian wine regions from 1910–2019. The potential drivers of these observed trends were then identified, including anthropogenic climate change and large-scale climate drivers (El Nino–Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), and Southern Annular Mode (SAM)). Methods and Results. The timing of budburst was approximated using accumulation measurements applied to Australia wide gridded temperature data. We show that the modelled budburst date has been gradually shifting to earlier in the year for most (95%) Australian wine regions, at an average rate of one day every 24 years. This linear trend in budburst timing is likely to be associated with steadily increasing air temperatures due to anthropogenic climate change. Significant interannual variability was also observed and was correlated with IOD and SAM; however, no significant relationship was found with ENSO. Positive IOD phases result in budburst occurring on average four days earlier than the long-term average; however, this can be as high as eight days. Conclusions. The results of this study highlight that budburst timing for wine grapes is not a stationary phenomenon and is influenced by both natural and anthropogenic conditions. Significance of the Study. Understanding variability and trends in modelled budburst timing will assist tactical and strategic management practices and improve phenological modelling and adaptation planning for climate change.

Predictability of extreme streamflow in Brazilian rivers through climate indices

In the present study empirical modeling was used to estimate extreme monthly streamflow in 161 locations of hydroelectric plants in the main Brazilians basins through a climate indices set. Principal components analysis was applied to capture the combined influences of climate indices variability. The main predictors of the models were climate patterns of tropical Atlantic and Pacific (Tropical Southern Atlantic and El Niño Southern Oscillation (ENSO) Modoki), complemented by high latitudes patterns (Antarctic Oscillation and Pacific North American Pattern). The contribution of the ENSO/Pacific Decadal Oscillation mode occurs in preferential months, especially in the transition seasons. There is also a contribution of the lagged streamflow itself, mainly in basins located in the Southeast of Brazil. The accuracy of the model for most of the Brazilian basins is higher than 70%, with higher values than 90% for the estimate of very low streamflow in northeast and north-central Brazil, as well as for very high streamflow in south-central region, which performance decreases with the increase in the lag. The results showed that the climate indices have a highly predictive potential for extreme streamflow, with a higher predictability for more long-term forecasts in case of very low streamflow than very high streamflow.

North-south antiphase of wildfire activity across the pyroregions of continental China driven by NAO and the Antarctic oscillation

Wildfires are a natural disturbance in many parts of the world, but fire regimes are changing as a result of anthropogenic pressures. A key uncertainty towards anticipating future changes in burned area lies in understanding the effects of climate teleconnections (CTs). Here we test how different CTs impact burned area in China, a large country comprising different biomes and where similar fire-suppression and post-fire afforestation policies are implemented. We observed diverging temporal trends in burned area across the different pyroregions of China, from increases in the Northeastern grasslands and mixed forests pyroregion to decreases in the Southern tropical forests pyroregion. This North-South antiphase in fire activity was being partly driven by joint effects of the North Atlantic Oscillation and the Antarctic Oscillation, which exerted contrasting effects on fire weather across latitude. El Niño Southern Oscillation and the other examined teleconnections had minor effects over burned area. The increasing burned area in the NE-mixed forests pyroregion indicates that mega-fires may increase under global warming but their occurrence may be modulated by potential strengthening or weakening of NAO and AAO.

Combined impact of ENSO and Antarctic Oscillation on austral spring precipitation in Southeastern South America (SESA)

Southeastern South America (SESA)’s precipitation is thought to be influenced by both El Niño Southern Oscillation (ENSO) and Antarctic Oscillation (AAO), especially in austral spring. Previous studies conclude AAO can modulate ENSO’s impact on precipitation over the SESA region without differentiating between El Niño and La Niña events. In the present study, we use composite analysis to further explore the combined impact of AAO and ENSO on austral spring precipitation over Southeastern South America (SESA) to answer this question and explain the dynamic mechanisms. We found that different AAO phases can influence La Niña’s impact on SESA austral spring precipitation considerably, while this does not apply for El Niño events. From our analysis, we found that AAO exerts more impact on austral spring precipitation over SESA compared to ENSO during La Niña years by influencing northerly wind and southward water vapor flux, which contributes most of the moisture into the SESA region, due to the strengthening of South Atlantic subtropical anticyclone and stronger meridional gradient in low-level pressure. Besides, there is an upper-level trough (ridge) over subtropical South America indicating advection of cyclonic (anticyclonic) vorticity inducing anomalous increase (decrease) of precipitation over that region during La Niña/AAO− (La Niña/AAO+). We do not see this opposite difference within El Niño groups combined with different phases of AAO.

Extreme harmful algal blooms, climate change, and potential risk of eutrophication in Patagonian fjords: Insights from an exceptional Heterosigma akashiwo fish-killing event

The Patagonian fjords have experienced intense harmful algal blooms (HABs) in the last decade, affecting important aquaculture areas in southern Chile. Climatic anomalies have recently triggered ‘super blooms’ of opportunistic toxic microalgal genera, especially due to persistent thermal stratification which likely provides an optimal niche for HABs development in fjord systems. In March-April 2021, an intense and widespread bloom of the raphidophyte Heterosigma akashiwo caused high salmon mortalities (>6,000 t) in the Comau fjord, Los Lagos Region. A climate variability analysis showed the effects of the positive phase of the Southern Annular Mode (SAM > 1.2 hPa) overcame those of La Niña (Niño3.4 = -0.9 °C) leading to an intense drought on the northern part of Patagonia with record low rainfall (the 2nd driest summer in the last 70 years) and increased water temperature. A regional satellite analysis revealed an extreme and persistent shallow Mixed Layer Depth (MLD) during summer periods since 2019 within the inland seas. In situ vertical fine-resolution measurements during the bloom event showed high cell abundances in the first 3 m of the water column (max. ∼ 70,000 cells mL−1), associated with warmer water temperature (∼15.5 – 17.5 °C), low salinity (∼25–30 psu), moderate to high dissolved oxygen (5 – 8.5 mg/L) and extremely high fluorescence signals in dense superficial cell aggregations (max. 74.9 µg/L). A 18S rRNA metabarcoding analysis formally confirmed the presence of H. akashiwo and its almost monospecific bloom development at the water surface. HPLC pigment analysis showed the carotenoid fucoxanthin in high proportion (48.8 %) compared to other photosynthetic pigments, becoming a potential pigment biomarker for early satellite H. akashiwo detection. Cell growth and cytotoxic in vitro experiments revealed high phenotypic plasticity of Chilean H. akashiwo against sudden changes in salinity. An RTgill-W1 gill cell assay revealed high cytotoxic activity (viability down to ∼ 50 – 30 % of controls) only at high cell abundances (>40,000H. akashiwo cells mL−1), which was in accordance with histological examination of moribund salmon that showed gill damage and circulatory disorders mainly due to long-term exposure to hypoxic conditions and not to potent cytotoxic effects. The Party-MOSA particles dispersion model revealed a high retention of water masses within the Comau fjord during the H. akashiwo outbreak, a scenario that may have boosted fish kills due to enhanced cells patchiness, ichthyotoxins persistence and hypoxic conditions. A historical dissolved inorganic nutrient data analysis showed that inner Patagonian fjords maintain low N and P concentrations including those environments considered of high eutrophication risk. Low N:P (<16:1) ratios measured at Comau fjord during the 2021 suggests that toxic flagellates growth could be favored over diatoms; however, low N:Si (<1:1 – N deficiency) evidences a clear need for better understanding of the role of mixotrophy in the persistence of the 2021H. akashiwo bloom for several weeks. These results highlight the fact that HABs responses against climate drivers and potential eutrophication are not universal and need to be assessed yearly and locally, particularly because extreme droughts and intensive aquaculture in northern Patagonia are expected to continue throughout the 21st century.

Interannual Variability of the 12‐hr Tide in the Mesosphere and Lower Thermosphere in 15 Years of Meteor‐Radar Observations Over Rothera (68°S, 68°W)

AbstractThe solar tides of the mesosphere and lower thermosphere (MLT) show great variability on time scales of days to years, with significant variability at interannual time scales. However, the nature and causes of this variability remain poorly understood. Here, we present measurements made over the interval 2005–2020 of the interannual variability of the 12‐hr tide as measured at heights of 80–100 km by a meteor radar over Rothera (68°S, 68°W). We use a linear regression analysis to investigate correlations between the 12‐hr tidal amplitudes and several climate indices, specifically the solar cycle (as measured by F10.7 solar flux), El Niño Southern Oscillation (ENSO), the Quasi‐Biennial Oscillation (QBO) at 10 and 30 hPa and the Southern Annular Mode (SAM). Our observations reveal that the 12‐hr tide has a large amplitude and a clearly defined seasonal cycle with monthly mean values as large as 35 m s−1. We observe substantial interannual variability, with monthly mean 12‐hr tidal amplitudes at 95 km exhibiting a two standard‐deviation range (2σ) in spring of 13.4 m s−1, 11.2 m s−1 in summer, 18.6 m s−1 in autumn, and 7.0 m s−1 in winter. We find that F10.7, QBO10, QBO30, and SAM all have significant correlations to the 12‐hr tidal amplitudes at the 95% level, with a linear trend also present. Whereas we detect very minimal correlation with ENSO. These results suggest that variations in F10.7, the QBO and SAM may contribute significantly to the interannual variability of 12‐hr tidal amplitudes in the Antarctic MLT.

Spatiotemporal change analysis for snowmelt over the Antarctic ice shelves using scatterometers

Using Scatterometer-based backscatter data, the spatial and temporal melt dynamics of Antarctic ice shelves were tracked from 2000 to 2018. We constructed melt onset and duration maps for the whole Antarctic ice shelves using a pixel-based, adaptive threshold approach based on backscatter during the transition period between winter and summer. We explore the climatic influences on the spatial extent and timing of snowmelt using meteorological data from automatic weather stations and investigate the climatic controls on the spatial extent and timing of snowmelt. Melt extent usually starts in the latter week of November, peaks in the end of December/January, and vanishes in the first/second week of February on most ice shelves. On the Antarctic Peninsula (AP), the average melt was 70 days, with the melt onset on 20 November for almost 50% of the region. In comparison to the AP, the Eastern Antarctic experienced less melt, with melt lasting 40–50 days. For the Larsen-C, Shackleton, Amery, and Fimbul ice shelf, there was a substantial link between melt area and air temperature. A significant correlation is found between increased temperature advection and high melt area for the Amery, Shackleton, and Larsen-C ice shelves. The time series of total melt area showed a decreasing trend of −196 km2/yr which was statistical significant at 97% interval. The teleconnections discovered between melt area and the combined anomalies of Southern Annular Mode and Southern Oscillation Index point to the high southern latitudes being coupled to the global climate system. The most persistent and intensive melt occurred on the AP, West Ice Shelf, Shackleton Ice Shelf, and Amery Ice Shelf, which should be actively monitored for future stability.