Study On The Structure Of Near Sea-surface Temperature Maximum In The Arctic And The Spatial Variation Of The Arctic Oscillation

The rapid chang of the Arctic sea ice plays a profound impact on the upper ocean and the climate system in the Arctic. The summertime CTD data during 1993-2008 are used to study the Near Sea-surface Temperature Maximum (NSTM) appeared at the depth less than 40m. The vertical structure, the forming mechanisms, the temporal variability and the temperature peak are discussed here. NSTM appears inside the conductive mixed layer formed in wintertime. Solar radiation heating and surface cooling are the basic mechanisms to form the NSTM in the water under sea ice. In the undisturbed open water, the NSTM can also appear so long as the surface cooling still exists. The NSTM occurred mainly within the depth range of 10-30m, and with the highest frequency in 20 m. Before 2003, the most NSTM were observed in marginal ice zone and open water, so the temperature maxima are usually above 0oC. After 2004, most NSTM occurred in ice-covered area with much lower temperature maxima. The annual period of NSTM is shown by ITP data, which occurred in summer and disappeared in spring in next year. The major temporal variation of NSTM is its warming and deepening. A simple analytical solution is presented to explain the mechanism of the warming and deepening by only considering the solar heating and surface cooling. The maximum temperature and the corresponding depth are related with not only the period of NSTM, but the latitude of the stations. The higher the latitude, the deeper the corresponding depth of maximum temperature of NSTM. The turbulent diffusivity is addressed as a key factor to determine the temperature maximum, the depth of the maximum, and the temporal variation rate. The NSTM is closely related with stratification, which prevents the upward heat transfer from the water below the pycnocline. Under the pycnocline, the solar energy mainly contributes to increase the temperature maximum. Above the pycnocline, the solar energy is mostly transported to sea ice by turbulent diffusion. The temperature maximum is sharpened by losing heat above the pycnocline.Arctic Oscillation (AO) is a seesaw pattern in which sea level pressure (SLP) at the polar and middle latitudes in North Hemisphere fluctuates between positive and negative phases. It has been used as a representative atmospheric circulation index to express climate change. The purpose of this paper is to reveal the regional difference of SLP variation. By calculating the correlation coefficients of AO Index with all the gridded SLPs, we have uncovered a special region named as Arctic Oscillation Core Region (AOCR), where the running correlation coefficients (RCC) between gridded SLP and AO index are all negative. The averaged SLP of this region correlates significantly with the AO index. The correlations between local SLPs and AO index outside of AOCR are weaker than those inside. RCC analysis reveals several strong discrepant events different from AO. These events occurred in the years of 1954, 1955, 1962, 1971, 1982/83, 1995, 1996/97, 1998, and 1999. A comparison of these events and the ENSO or PDO indices suggests that the events in 1982/83 and 1998 are probably associated with the ENSO processes. Events centered in other years are likely connected with PDO, which reached their minima in the years of 1950, 1955, 1962 and 1971. The result in this study provides an alternative insight to look at the mechanism of the variation of Arctic Oscillation.The positive and negative AO-dominant regions show that the SLP oscillated sometimes between the polar and mid-latitude regions and sometimes between land and ocean. Along the Atlantic–Pacific section, the North Atlantic Oscillation exists as a stationary seesaw-like dipole, while on the Pacific side the oscillation is intermittent with lower intensity and swinging boundary. The long-term spatial variation of the AO with three stages is clearly identified by the relative area of the SLP anomaly regions. Positive SLP anomaly area dominated before 1970, showing the state before the global warming. Negative SLP anomaly area dominated during 1971–1995, indicating the effect of global warming before the Arctic warming being apparent. Since 1996 both positive and negative SLP anomaly areas are all small, being possibly caused by the sea-ice retreat during the Arctic warming.