Net Modulation of Upper Ocean Thermal Structure by Typhoon Kalmaegi (2014)

Abstract

In situ observation of a buoys/moorings array and a model simulation were used to study the modulation of upper ocean thermal structure by Typhoon Kalmaegi in September 2014. The inertial period signals were significant after forcing of Kalmaegi, but they did not account for the net heat change. Removing the inertial period signals showed that the net thermal response biased to the right of Kalmaegi's track. Vertical mixing caused surface cooling with an inverted-cone structure and subsurface warming with a double-wing structure. Net upwelling converted the left wing of the subsurface warming to cooling, while net downwelling warmed the upper ocean in front and on both sides of the net upwelling zone. Horizontal advection was not as important as vertical mixing and vertical advection in modulating the thermal structure but contributed to the net outward advection of thermal anomaly in the mixed layer during the forced stage and also in the net along-track recovery of subsurface anomaly during the relaxation stage. In general, horizontal and vertical advection modulated thermal anomalies in the upper ocean across a broader horizontal range and into the deeper ocean compared with the effect of vertical mixing. Our results indicate the need to consider both mixing and advection (rather than only mixing) when studying the effects of tropical cyclones on local ocean heat uptake and global ocean heat transport.Plain Language Summary Tropical cyclones are strong natural phenomena occurring on the ocean. Tropical cyclones intensify ocean mixing and deepen surface mixed layer (defined as a layer with uniform temperature). In so doing, it creates cold anomaly at the surface and warm anomaly in the subsurface, which can be considered as a downward pump of warm water (heat pump effect). The subsurface warming cannot be directly recovered by air-sea surface interaction; it may stay in the ocean and contribute to global ocean heat transport and then influence the climate system. This work studied the upper ocean thermal response to a tropical cyclone (typhoon Kalmaegi) in September 2014. The results show that besides the surface cooling and subsurface warming, typhoon Kalmaegi also cools the subsurface by an upwelling process. Upwelling brings up cold water, and part of subsurface warming is modulated outside of the main response area and into the deeper ocean (cold suction effect). This work indicates that the upper ocean thermal response to a tropical cyclone is more complicated than only heat pump effect. Cold suction effect needs to be taken into consideration when estimating the tropical cyclones' contribution to global ocean heat budget.

Ocean Response to Successive Typhoons Sarika and Haima (2016) Based on Data Acquired via Multiple Satellites and Moored Array

“…The numerical model used in this study was a three-dimensional version of the Price-Weller-Pinkel model (3DPWP) [54,55], which has been used successfully in previous studies to simulate and understand the physical processes involved in the oceanic response to a TC [15][16][17]22,[56][57][58]. The model domain used here spans 1200 km in the across-track direction and 5600 km in the along-track direction, with a horizontal resolution of 8 km and a vertical resolution of 10 m with the ocean depth of 1450 m. The time resolution is 120 s. The model starts from rest, and the initial temperature and salinity were set to be horizontally homogeneous using the average profiles from Station 2 during UTC 00:00 on 14 October to UTC 00:00 on 16 October for Sarika and during UTC 00:00 on 18 October to UTC 00:00 on 20 October for Haima (see Figure 2).…”

“…The near-inertial current normally decays within 5-20 inertial periods and propagates both horizontally and vertically in the ocean [20,21]. The near-inertial current is accompanied by alternative upwelling and downwelling (near-inertial pumping) [22], which is asymmetric with a rapid transition from a maximum in the downwelling phase to a maximum in the upwelling phase, followed by a gradual transition to the next downwelling maximum [23,24]. The horizontal and vertical propagation of the near-inertial current results in wave dispersion and propagation of kinetic energy [10,16,25,26], which can also generate super-inertial internal waves such as double-inertial frequency (2f ) waves [27,28] that contribute to the energy cascade toward dissipation.…”

“…The sea surface temperature (SST) cooling was usually by 1-6 • C [2,4,[31][32][33][34][35], and by more than 10 • C in some extreme cases [36,37]. Owing to the rightward (or leftward) bias of the current response, the temperature response is also usually biased to the right side (or left side) of the TC track in the Northern (or Southern) Hemisphere [15,22]. Besides mixing, the vertical advection (upwelling and downwelling) and horizontal advection can also modulate the oceanic temperature structure.…”

“…Besides mixing, the vertical advection (upwelling and downwelling) and horizontal advection can also modulate the oceanic temperature structure. In general, the subsurface warm anomaly can be strengthened or weakened by upwelling or downwelling [15,22,38], and the effect of horizontal advection depends on the current speed and horizontal temperature gradient [22]. The vertical advection mainly influences the subsurface and deeper ocean, as Argo data reveal that upwelling contributes an average of 15% of the cooling in the near-surface layer (10-30 m), 84% in the subsurface layer (30-250 m), and 94% in the deep layer (250-600 m) during the period of 0.5-2.5 days after the passage of a typhoon [39].…”

Response of Coastal Water in the Taiwan Strait to Typhoon Nesat of 2017

“…Furthermore, our previous works (e.g., [2,50,[88][89][90][91][92][93]) indicate thatoceanic thermohaline and dynamic features play an important role in upper ocean response to a single or sequential typhoons based on multiple observation data and model simulations. However, these works were mainly in the marginal sea (the South China Sea) and we may further follow the study of this paper, and study how some special topographic features such as with many islands or straits influences the structure of the oceanic response to typhoons in the future.…”