A Paleoclimate Reconstruction of the Little Ice Age to Modern Era Climate Conditions in the Eastern Ross Sea, Antarctica as Captured in the RICE Ice Core

<p>The Little Ice Age (LIA) (1400-1850 AD) represents one of the most significant climatic shifts over the past 5000 years. Previous studies from Antarctica indicate generally cooler and stormier conditions during this period, but this pattern shows distinct spatial and temporal variability. The Roosevelt Island Climate Evolution (RICE) ice core provides a new opportunity to study the drivers behind this variability at annual/seasonal resolution, in a relatively under-sampled and climatically sensitive region in the eastern Ross Sea. Contrary to previous studies, isotope measurements suggest warm conditions during the LIA at Roosevelt Island. This study presents analysis of eight major ions (Na⁺, Mg²⁺, Ca²⁺, K⁺, MS⁻, Cl⁻, NO₃⁻, SO₄²⁻) using both Ion Chromatograph and ICP-MS data, in order to reconstruct the atmospheric circulation pattern, sea ice extent and marine primary productivity across this LIA to Modern Era (ME) at Roosevelt Island. The dataset is tied to a robust age model allowing annual dating and the opportunity to accurately reconstruct rates of change during this ME-LIA. Challenges revolving around the calibration of the Ion Chromatograph are also discussed. The major ion record determines whether the lack of cooling in the Roosevelt Island core implied by the stable isotopes represents a true temperature anomaly or whether the atmospheric circulation pattern caused an isotopic enrichment that masks an underlying cooling. It was determined that Roosevelt Island experienced during the LIA (i) an increase in marine air mass intrusions along with weaker katabatic winds compared to the 200 years prior, (ii) decreased biological productivity and (iii) increased sea ice. From the 1850-1880s to 1992 AD, there is a shift to reduced marine winds, increased katabatics, increased biological productivity and decreased sea ice until 1992. In the wider Ross Sea context, this suggests an east-west divide in terms of the dominance of katabatics versus marine wind influence. This divide is attributed with the warming signal seen in the RICE record in the Eastern Ross Sea and the cooling in the Western Ross Sea records. It is also likely linked to the influence of climate indices on the depth/position of the Amundsen Sea Low.</p>

A Paleoclimate Reconstruction of the Little Ice Age to Modern Era Climate Conditions in the Eastern Ross Sea, Antarctica as Captured in the RICE Ice Core

<p>The Little Ice Age (LIA) (1400-1850 AD) represents one of the most significant climatic shifts over the past 5000 years. Previous studies from Antarctica indicate generally cooler and stormier conditions during this period, but this pattern shows distinct spatial and temporal variability. The Roosevelt Island Climate Evolution (RICE) ice core provides a new opportunity to study the drivers behind this variability at annual/seasonal resolution, in a relatively under-sampled and climatically sensitive region in the eastern Ross Sea. Contrary to previous studies, isotope measurements suggest warm conditions during the LIA at Roosevelt Island. This study presents analysis of eight major ions (Na⁺, Mg²⁺, Ca²⁺, K⁺, MS⁻, Cl⁻, NO₃⁻, SO₄²⁻) using both Ion Chromatograph and ICP-MS data, in order to reconstruct the atmospheric circulation pattern, sea ice extent and marine primary productivity across this LIA to Modern Era (ME) at Roosevelt Island. The dataset is tied to a robust age model allowing annual dating and the opportunity to accurately reconstruct rates of change during this ME-LIA. Challenges revolving around the calibration of the Ion Chromatograph are also discussed. The major ion record determines whether the lack of cooling in the Roosevelt Island core implied by the stable isotopes represents a true temperature anomaly or whether the atmospheric circulation pattern caused an isotopic enrichment that masks an underlying cooling. It was determined that Roosevelt Island experienced during the LIA (i) an increase in marine air mass intrusions along with weaker katabatic winds compared to the 200 years prior, (ii) decreased biological productivity and (iii) increased sea ice. From the 1850-1880s to 1992 AD, there is a shift to reduced marine winds, increased katabatics, increased biological productivity and decreased sea ice until 1992. In the wider Ross Sea context, this suggests an east-west divide in terms of the dominance of katabatics versus marine wind influence. This divide is attributed with the warming signal seen in the RICE record in the Eastern Ross Sea and the cooling in the Western Ross Sea records. It is also likely linked to the influence of climate indices on the depth/position of the Amundsen Sea Low.</p>

Aral's potential sources of dust for Moscow region

Array of 7-day backward trajectories of air particles for Moscow were simulated for days of measurement of volume concentrations of aerosols with particle sizes of 0.1-1.0, 1.0-2.5 and 2.5-5.0 μm at the AERONET site in Moscow in 2001-2018. The CWT (concentration weighted trajectory) method, modified for the atmosphere column, was used to determine the potential sources of aerosols of these three fractions for Moscow region. Potential sources of extreme concentrations of these aerosols in the Moscow atmosphere and the atmospheric circulation pattern favored of their transport to Moscow have been identified.

Changes in the Relationship between ENSO and Asia–Pacific Midlatitude Winter Atmospheric Circulation

Interdecadal changes in the relationship between El Niño–Southern Oscillation (ENSO) and midlatitude atmospheric circulation are investigated in this study. Comparison of associations between ENSO and midlatitude atmospheric circulation anomalies between 1958–76 and 1977–2010 suggest that during 1958–76, ENSO exerted a strong impact on the East Asian winter monsoon (EAWM) and the associated atmospheric circulation pattern was similar to the positive North Pacific Oscillation (NPO). In contrast, during 1977–2010, the NPO-like atmospheric pattern disappeared. Instead, ENSO exerted a strong impact on the eastern North Pacific Ocean (NP) and North America, and the associated atmospheric circulation pattern resembled the Pacific–North America (PNA) teleconnection. Also, significant correlations between ENSO and sea surface temperature anomalies (SSTAs) over the western subtropical NP during 1958–76 became insignificant during 1977–2010, whereas negative correlations between ENSO and SSTAs in the central and northeastern subtropical NP became more significant since the mid-1970s. Further analyses suggest that the interdecadal shift of the Aleutian low, which occurred around the mid-1970s, might be responsible for the identified changes. Before the mid-1970s, warm ENSO events generated an anomalous anticyclone over the western NP, which is a key system bridging ENSO and EAWM-related atmospheric circulation. After the mid-1970s, the Aleutian low intensified and shifted eastward, leading to the impact of ENSO prevailing over the eastern NP. In addition, the weakened (strengthened) ENSO–NPO/EAWM (ENSO–PNA) relationship likely contributed to the weakened (strengthened) relationship between ENSO and SSTAs over the western (central and eastern) subtropical NP.

Season-Dependent Forecast Skill of the Leading Forced Atmospheric Circulation Pattern over the North Pacific and North American Region*

Multimodel ensemble (MME) seasonal forecasts are analyzed to evaluate numerical model performance in predicting the leading forced atmospheric circulation pattern over the extratropical Northern Hemisphere (NH). Results show that the time evolution of the leading tropical Pacific sea surface temperature (SST)-coupled atmospheric pattern (MCA1), which is obtained by applying a maximum covariance analysis (MCA) between 500-hPa geopotential height (Z500) in the extratropical NH and SST in the tropical Pacific Ocean, can be predicted with a significant skill in March–May (MAM), June–August (JJA), and December–February (DJF) one month ahead. However, most models perform poorly in capturing the time variation of MCA1 in September–November (SON) with 1 August initial condition. Two possible reasons for the models’ low skill in SON are identified. First, the models have the most pronounced errors in the mean state of SST and precipitation along the central equatorial Pacific. Because of the link between the divergent circulation forced by tropical heating and the midlatitude atmospheric circulation, errors in the mean state of tropical SST and precipitation may lead to a degradation of midlatitude forecast skill. Second, examination of the potential predictability of the atmosphere, estimated by the ratio of the total variance to the variance of the model forecasts due to internal dynamics, shows that the atmospheric potential predictability over the North Pacific–North American (NPNA) region is the lowest in SON compared to the other three seasons. The low ratio in SON is due to a low variance associated with external forcing and a high variance related to atmospheric internal processes over this area.