Xuezhi Bai

Is the Dipole Anomaly a major driver to record lows in Arctic summer sea ice extent

] Recent record lows of Arctic summer sea ice extentare found to be triggered by the Arctic atmospheric DipoleAnomaly (DA) pattern. This local, second–leading mode ofsea–level pressure (SLP) anomaly in the Arctic produced astrong meridional wind anomaly that drove more sea ice outof the Arctic Ocean from the western to the eastern Arcticinto the northern Atlantic during the summers of 1995,1999, 2002, 2005, and 2007. In the 2007 summer, the DAalso enhanced anomalous oceanic heat flux into the ArcticOceanviaBeringStrait,whichacceleratedbottomandlateralmelting of sea ice and amplified the ice–albedo feedback. Acoupled ice–ocean model was used to confirm the historicalrecord lows of summer sea ice extent.

Temporal and Spatial Variability of Great Lakes Ice Cover, 1973–2010*

AbstractIn this study, temporal and spatial variability of ice cover in the Great Lakes are investigated using historical satellite measurements from 1973 to 2010. The seasonal cycle of ice cover was constructed for all the lakes, including Lake St. Clair. A unique feature found in the seasonal cycle is that the standard deviations (i.e., variability) of ice cover are larger than the climatological means for each lake. This indicates that Great Lakes ice cover experiences large variability in response to predominant natural climate forcing and has poor predictability. Spectral analysis shows that lake ice has both quasi-decadal and interannual periodicities of ~8 and ~4 yr. There was a significant downward trend in ice coverage from 1973 to the present for all of the lakes, with Lake Ontario having the largest, and Lakes Erie and St. Clair having the smallest. The translated total loss in lake ice over the entire 38-yr record varies from 37% in Lake St. Clair (least) to 88% in Lake Ontario (most). The tot...

Interannual variability of Great Lakes ice cover and its relationship to NAO and ENSO

[1] The impacts of North Atlantic Oscillation (NAO) and El Nino–Southern Oscillation (ENSO) on Great Lakes ice cover were investigated using lake ice observations for winters 1963–2010 and National Centers for Environmental Prediction reanalysis data. It is found that both NAO and ENSO have impacts on Great Lakes ice cover. The Great Lakes tend to have lower (higher) ice cover during the positive (negative) NAO. El Nino events are often associated with lower ice cover. The influence of La Nina on Great Lakes ice cover is intensity-dependent: strong (weak ) La Nina events are often associated with lower (higher) ice cover. The interference of impacts of ENSO and NAO complicates the relationship between ice cover and either of them. The nonlinear effects of ENSO on Great Lakes ice cover are important in addition to NAO effects. The correlation coefficient between the quadratic Nino3.4 index and ice cover (� 0.48) becomes significant at the 99% confidence level. The nonlinear response of Great Lakes ice cover to ENSO is mainly due to the phase shift of the teleconnection patterns during the opposite phases of ENSO. Multiple-variable nonlinear regression models were developed for ice coverage. Using the quadratic Nino3.4 index instead of the index itself can significantly improve the prediction of Great Lakes ice cover (the correlation between the modeled and observed increases from 0.35 to 0.51). Including the interactive term

Cold Water and High Ice Cover on Great Lakes in Spring 2014

Very cold temperatures across much of North America caused by the recent anomalous meridional upper air flow—commonly referred to in the public media as a polar vortex (for details, see Blackmon et al. [1977] and National Climatic Data Center, State of the climate: Synoptic discussion for January 2014, http://www.ncdc.noaa.gov/sotc/synoptic/2014/1)—have contributed to extreme hydrologic conditions on the Great Lakes. The Great Lakes are the largest system of lakes and the largest surface of freshwater on Earth—Lake Superior alone is the single largest lake by surface area.

A modeling study of coastal circulation and landfast ice in the nearshore Beaufort and Chukchi seas using CIOM

This study investigates sea ice and ocean circulation using a 3-D, 3.8 km CIOM (Coupled Ice-Ocean Model) under daily atmospheric forcing for the period 1990–2008. The CIOM was validated using both in situ observations and satellite measurements. The CIOM successfully reproduces some observed dynamical processes in the region, including the Bering-inflow-originated coastal current that splits into three branches: Alaska Coastal Water (ACW), Central Channel branch, and Herald Valley branch. In addition, the Beaufort Slope Current (BSC), the Beaufort Gyre, the East Siberian Current (ESC), mesoscale eddies, and seasonal landfast ice are well simulated. The CIOM also reproduces reasonable interannual variability in sea ice, such as landfast ice, and anomalous open water (less sea ice) during the positive Dipole Anomaly (DA) years, vice versa during the negative DA years. Sensitivity experiments were conducted with regard to the impacts of the Bering Strait inflow (heat transport), onshore wind stress, and sea ice advection on sea ice change, in particular on the landfast ice. It is found that coastal landfast ice is controlled by the following processes: wind forcing, Bering Strait inflow, and sea ice dynamics.

Abrupt Climate Changes and Emerging Ice-Ocean Processes in the Pacific Arctic Region and the Bering Sea

The purpose of this chapter is to reveal several emerging physical ice-ocean processes associated with the unprecedented sea ice retreat in the Pacific Arctic Region (PAR). These processes are closely interconnected under the scenario of diminishing sea ice, resulting in many detectable changes from physical environment to ecosystems. Some of these changes are unprecedented and have drawn the attention of both scientific and societal communities. More importantly, some mechanisms responsible for the diminishing sea ice cannot be explained by the leading Arctic Oscillation (AO), which has been used to interpret most of the changes in the Arctic for the last several decades. The new challenging questions are: (1) What is the major forcing? (2) Is the AO, the DA, or their combination, contributing to the sea ice minima in recent years? How do we use models to investigate the recent changes in the PAR. Is the heat transport through the Bering Strait associated with the DA? What processes accelerate sea ice melting in the PAR?

A modeling study of the effects of river runoff, tides, and surface wind-wave mixing on the Eastern and Western Hainan upwelling systems of the South China Sea, China

This study investigates the variation of eastern Hainan (or Qiongdong) and western Hainan upwelling systems during the East Asia summer monsoon (EASM) season using a state-of-the-art finite-volume coastal model and reveals the impacts of tidal mixing, surface wind-wave mixing, and river runoff on the Hainan upwellings in terms of the spatial and temporal variations, intensification, and vertical structure. It is found that (1) river runoff, a stabilizer of the water column, suppresses the upwelling beneath it from reaching the surface, although strong upwelling still occurs in the lower layer of the water column; (2) tidal mixing, a mechanism of forming bottom mixed layer, promotes upwelling, leading to strengthening of the upwelling; (3) surface wind-wave mixing, a major mechanism for formation of the upper mixed layer and a sharp thermocline, inhibits the upwelling from crossing the thermocline to reach the surface; and (4) unlike the east coast upwelling, the upwelling on the west coast is tidally induced.