Effects of thermocline structure variations on acoustic propagation in convergence zone

A model that provides a connection between deep-ocean thermocline intensity and convergence zone(CZ) phenomena is presented based on ray theory under the condition of a two layer linear sound speed profile(SSP).The relationship between environmental variability(such as main thermocline intensity,main thermocline depth and seasonal thermocline structure) and distance and width of CZ was analyzed using a new variable of minimum displacement angles(MDA).The results showed that the thermocline structure greatly influences CZ features.An increase in the thermocline intensity causes the CZ to shift away from the source,and the increment of CZ can be 3.5～5.0 km if the thermocline intensity increases at a rate of 0.01 s-1.The thermocline position has a smaller influence on CZ than thermocline intensity.In comparison with two-layer linear SSP,the CZ shifts close to the source when an up-type structure is used.The decrement of CZ can be 1.0～1.5 km in thermocline conditions deepening to 200 m.In contrast,if the CZ shifts away from the source with a down-type structure,the increment of CZ can be 1.0～1.5 km in mixed-layer conditions deepening to 200 m.The CZ is nearer when the thermocline becomes shallow with an up-type structure,and it is further when the thermocline becomes deep with a down-type structure The existence of a seasonal thermocline causes complicated variabilities in a certain layer near the ocean surface,including a negative gradient,zero gradient,and positive gradient.The relationship between seasonal thermocline intensity and CZ with negative gradient SSP is similar to that of the main thermocline,but to a smaller degree.A surface duct is formed with a positive gradient SSP,and the increase in the gradient causes the CZ to be near the source.