Research On Characteristic Of Information Transmission In Ocean-Atmosphere Coupling System Based On Information Theory

Air-sea interaction is one of the driving forces of atmospheric motion and climate change. Information transmission occur with transmission and mass transmission, while transmission and mass transmission occur in air-sea interaction In this paper, information transmission in ocean-atmosphere coupling system(OACS) is the core scientific issue. Based on sea surface temperature (SST), geopotential height on 850hPa (H850), ocean water temperature (OWT) on 75m and 700m depth (OWT75 and OWT700), spatial mode and vertical structure of information transmission in OACS are explored to establish a global map of information transmission. Seasonal variations and decadal changes are discussed also. On the basis, the key regions of sea surface are extracted to build a synergy model of atmosphere response to SST. By discussing information transmission between tropical Central and Eastern Pacific and low-latitude atmosphere, asymmetry of information transmission of ENSO is revealed. H850 represents atmosphere, SST for sea surface to OWT and for ocean to H850, OWT75 for ocean on 75m, and OWT700 for ocean on 700m. Research on characteristic of information transmission in OACS provides a new perspective to explore air-sea interaction, and the main conclusions are as follows:(1) Spatial mode and vertical structure of information transmission in OACS. For information transmission between SST and H850, tropical ocean is information source while mid-latitude ocean in information transmission balance, and mid-latitude atmosphere is information sink as well as atmosphere over tropical Eastern Tropical Pacific and southern of East Asian. For information transmission between SST and OWT75, sea surface of tropical Central and Eastern Pacific is information source, and sea surface of mid-latitude in Northern Hemisphere is information sink, while sea surface of mid-latitude in Southern Hemisphere is in information transmission balance; Ocean on 75m of tropical Central and Eastern Pacific, North Atlantic and west coast of North America continent are information source, Ocean on 75m north of 60°N and 30°S-60°S are information sink, while Ocean on 75m of mid-latitude in Northern Hemisphere is in information transmission balance. For information transmission between SST and OWT700, sea surface of tropical Central and Eastern Pacific is weak information source, sea surface of mid-latitude in Northern Hemisphere is information sink, as well as 30°S, while other areas are in information transmission balance; Ocean on 700m is information source, especially in the area of warm current. Decay rates of import information of geopotential height from low layer to high layer are different on different latitudes, and the fastest in equatorial. Import information of OWT gradually decrease by depth increase, and the differences of the rate are not big on different latitudes, while export information of OWT is stable by depth increase, but the differences of the rate are big on different latitudes.850hPa is key layer for atmosphere, and 75m is key depth for ocean.(2) Global map of information transmission in OACS. Sea surface of tropical Central and Eastern Pacific receives information from solar radiation, then transport information up to tropical atmosphere and down to tropical ocean. Tropical atmosphere can transport information to mid-latitude atmosphere. Tropical ocean can transport information to mid-latitude ocean by strengthen western boundary current also, and then mid-latitude ocean and mid-latitude atmosphere are in information transmission balance. The deeper ocean can transport information to sea surface or in information transmission balance with sea surface by key current. So tropical ocean is key.(3) Seasonal variations of information transmission in OACS. For information transmission between SST and H850, Northern Hemisphere ocean export more information in summer, and Southern Hemisphere ocean export more information in winter, while tropical ocean export more information in spring and autumn. The results indicate that intensity of ocean export information is interrelated to absorption energy from solar radiation by ocean. Southern Hemisphere atmosphere import more information in summer, and Northern Hemisphere atmosphere import more information in winter, while distribution of atmosphere import information is almost symmetric around equator in spring and autumn. The results show that atmosphere in winter hemisphere import more information from ocean and this is consistent with latent heat flux also. Related to information transmission between SST and OWT75, sea surface in Northern Hemisphere import more information in winter while sea surface in Southern Hemisphere import more information in summer, and sea surface in Northern Hemisphere import more information in spring and autumn. The results point out that North Pacific and North Atlantic play an important role on maintain energy balance. Ocean on 75m in Northern Hemisphere exports more information in summer and autumn, while ocean on 75m in Southern Hemisphere exports more information in winter and spring. The above indicates that distribution of export information of ocean on 75m corresponds to incident point of sun light. For information transmission between SST and OWT700, export information of ocean on 700m maintains in low-latitude for different seasons, and import information of sea surface is obviously seasonal. But the amplitude of seasonal variations gradually decrease, which is related to seasonal variability of H850, SST, OWT75 and OWT700 in mid-latitude.(4) Asymmetry of information transmission of ENSO. Information transmission from ocean to atmosphere is the main feature in El Nino state, as well as La Nina and Neutral. Relative to Neutral, the intensity of information transmission is stronger in El Nino and La Nina; Compared to El Nino, the intensity of information transmission is slightly stronger than that in La Nina. By rearrangement slide random sample (RSRS), the relationship between SST anomalies (SSTA) over the tropical eastern Pacific and the intensity of information transmission is analyzed, focused on the asymmetry of information transmission. Three stages are identified from the relationship:Liked La Nina, Liked Neutral and Liked El Nino. As cold SST weakening, information transmission weaken in Liked La Nina stage; as cold SST to warm SST, information transmission does not exist significant trends in Liked Neutral stage; as warm SST enhanced, information transmission enhance in Liked El Nino stage. The asymmetry exists in the air-sea interaction. When information from ocean to atmosphere is stronger, information from atmosphere to ocean is stronger.(5) Decadal changes of information transmission in OACS. After 1979/1980, the ocean, where information transmission enhancement dominate in winter, include tropical Central and Eastern Pacific around equator, tropical east-south Indian Ocean, tropical west-north Indian Ocean, and tropical North Atlantic, while information transmission weaken in the rest of tropical ocean. Information transmission strengthens in tropical Central and Eastern Pacific around equator in summer, and weakens in extra-equator, but the center of enhancement lies in south of 10°S also. And Information transmission strengthens in equatorial east Indian Ocean and tropical west-north Indian Ocean, while weakens in the remaining of tropical Indian Ocean. In tropical Atlantic the change in summer is the same as that in winter.1970s later, the change of information transmission of atmosphere is inconsistent in Southern Hemisphere and Northern Hemisphere. Information transmission of atmosphere in Southern Hemisphere strengthens in winter as well as in summer, while Information transmission of atmosphere in Northern Hemisphere strengthens in summer and weakens in winter but in Eurasia information transmission of atmosphere weakens in winter and summer. The decadal changes of information transmission associated with the decadal changes of inter-annual variability of ocean, whether in winter or in summer, as well as atmosphere. Obviously PDO is negative phase before 1979/1980, and then change to positive phase. The upper ocean is warming significantly, but seasonal variations and regional disparity is significant also. And the variability of global ocean increases obviously 1979/1980 later, but the variability decreases in partial of tropical Central and Eastern Pacific, which is almost symmetric around equator. The above is a possible cause which results in declining of indicative function of ENSO.1970S later, geopotential height increases in tropical region, which is related to global warming. But Aleutian Low strengthens significantly also, which is another characteristic. The variability of atmosphere decrease in Northern Hemisphere, and increase in Southern Hemisphere when winter-half-year, while the variability of global atmosphere increase when summer-half-year, except Eurasia. Turbulent heat flux in ocean-atmosphere interface, mainly latent heat flux, increases in North Pacific and decrease in other oceans. (6) Synergy model of key sea surface. Based on the research on characteristics of information transmission in OACS, thirteen key areas of sea surface are extracted. Then the key area of atmosphere is picked up by information transmission from SST anomaly index of key sea surface to atmosphere. Through information transmission and linear regression, five key areas of sea surface are selected from the thirteen with higher impact on atmosphere as the standard. The synergy model is established by the five key areas, and a possible SST pattern is proposed also. When PDO is positive phase, a positive SPDO (South Pacific Decadal Oscillation) will match it. The decadal SST background tends to warm in tropical Central and Eastern Pacific, and El Nino is easier to occur. Tropical Indian Ocean is warmer and SIOD (South Indian Ocean Dipole) is positive phase, while north Atlantic near Greenland is colder. The climate of next year is dominant by El Nino, and the anomaly east wind is stronger from Maritime continent to tropical north Indian Ocean, and vice versa.