13:45 〜 15:15
[AAS04-P13] Water pressure drop at 5000m-deep seafloor directly below the central air pressure drop of the Typhoon 201514
キーワード：台風、海底水圧、伊豆－小笠原
Introduction:
In a period from May 2015 to May 2016, we made an array observation of water pressure using ocean-bottom pressure gauges (Absolute depth sensor PARO-8B7000-I-005, Paroscientific, Inc., Redmond, WA, US). The 10-station array consisted of equilateral triangles with the minimum and maximum side-lengths of 10 and 30 km, respectively, on the relatively flat seafloor at depths of around 5000 m to the west of the steep slope of the northern Bonin Trench (Fig.3). The main objective of this observation was to detect any events of seafloor deformation associated with seismic and aseismic slips along the Izu-Bonin Trench. Besides the events directly relevant to this subject (1), we sometimes encounter records exhibiting intriguing phenomena of meteorologic or oceanic origin. We here report one of such examples, the deep ocean bottom response to the central air pressure drop of a typhoon.
Observation:
Figure 1 shows the residual records at the 8 stations of the array during the 34 days period from 25th of July, 2015. The residual is meant to be the rest of the original record after subtraction of a reference. We adopt a tide-resolving ocean circulation model JCOPE-T (2) as the reference. The records show two distinct pressure drop events, one associated with Typhoon 201514 (Molave) and the other with Typhoon 201516 (Astani). The two events followed the mutually similar tracks on the northwestern Pacific (Fig.2), although the whole Astani track was shifted about 200 km to the east relative to the Molave track. When the Molave passed through the array (Figs.2), the central air pressure experienced a maximum drop of 20 hPa (Fig.3) and at this timing the ocean bottom pressure records showed a maximum drop of 20 hPa consistently (Fig.1). This may imply the near-equality of the central air pressure drop with the ocean bottom pressure drop directly below it. When the Astani passed through the nearest point to the array (200 km to the east of the array), on the other hand, the central air pressure drop was as large as 50 hPa, yet the ocean bottom pressure drop at the array was less than 20 hPa (Fig.1). This may imply decay of ocean bottom pressure drop in the radial direction away from the central maximum drop right underneath the central air pressure drop.
Interpretation:
We have shown that the central air pressure drop of the Molave was nearly equal to the water pressure drop at the 5000m-deep seafloor right below it. This near equality may imply large velocity anomaly in the water column from the sea surface all the way down to the bottom in the typhoon system.
References:
Y. Fukao, T. Kubota, H. Sugioka, A. Ito, T. Tonegawa, H. Shiobara, M. Yamashita, T. Saito, Detection of “rapid” aseismic slip at the Izu-BoninTrench. J. Geophys. Res. Solid Earth 126, e2021JB022132 (2021). doi:10.1029/2021JB022132
S. M. Varlamov, X. Guo, T. Miyama, K. Ichikawa, T. Waseda, Y. Miyazawa. M2 baroclinic tide variability modulated by the ocean circulation south of Japan. J. Geophys. Res. Oceans 120, 3681-3720 (2015). doi:10.1002/2015JC010739
Figure captions:
Fig.1. Residual (Original-Reference) records at the 8 stations of the array during the 34 days period from 2015-07-24, 17:06:40. Two pressure drop events correspond to Typhoon 201514 and Typhoon 201516.
Fig.2. Track of the central pressure drop of Typhoon 201514 (Molave) (http://agora.ex.nii.ac.jp/digital-typhoon/summary/wnp/s/201514.html.en). The arrow shows the array location.
Fig.3. The array configuration on the deep seafloor to the west of the Izu-Bonin Trench. Typhoon 201514 passed through the eastern part of the array. The pathway of the typhoon is shown by blue diamond containing information about air pressure (hPa) at time (day and hour).
In a period from May 2015 to May 2016, we made an array observation of water pressure using ocean-bottom pressure gauges (Absolute depth sensor PARO-8B7000-I-005, Paroscientific, Inc., Redmond, WA, US). The 10-station array consisted of equilateral triangles with the minimum and maximum side-lengths of 10 and 30 km, respectively, on the relatively flat seafloor at depths of around 5000 m to the west of the steep slope of the northern Bonin Trench (Fig.3). The main objective of this observation was to detect any events of seafloor deformation associated with seismic and aseismic slips along the Izu-Bonin Trench. Besides the events directly relevant to this subject (1), we sometimes encounter records exhibiting intriguing phenomena of meteorologic or oceanic origin. We here report one of such examples, the deep ocean bottom response to the central air pressure drop of a typhoon.
Observation:
Figure 1 shows the residual records at the 8 stations of the array during the 34 days period from 25th of July, 2015. The residual is meant to be the rest of the original record after subtraction of a reference. We adopt a tide-resolving ocean circulation model JCOPE-T (2) as the reference. The records show two distinct pressure drop events, one associated with Typhoon 201514 (Molave) and the other with Typhoon 201516 (Astani). The two events followed the mutually similar tracks on the northwestern Pacific (Fig.2), although the whole Astani track was shifted about 200 km to the east relative to the Molave track. When the Molave passed through the array (Figs.2), the central air pressure experienced a maximum drop of 20 hPa (Fig.3) and at this timing the ocean bottom pressure records showed a maximum drop of 20 hPa consistently (Fig.1). This may imply the near-equality of the central air pressure drop with the ocean bottom pressure drop directly below it. When the Astani passed through the nearest point to the array (200 km to the east of the array), on the other hand, the central air pressure drop was as large as 50 hPa, yet the ocean bottom pressure drop at the array was less than 20 hPa (Fig.1). This may imply decay of ocean bottom pressure drop in the radial direction away from the central maximum drop right underneath the central air pressure drop.
Interpretation:
We have shown that the central air pressure drop of the Molave was nearly equal to the water pressure drop at the 5000m-deep seafloor right below it. This near equality may imply large velocity anomaly in the water column from the sea surface all the way down to the bottom in the typhoon system.
References:
Y. Fukao, T. Kubota, H. Sugioka, A. Ito, T. Tonegawa, H. Shiobara, M. Yamashita, T. Saito, Detection of “rapid” aseismic slip at the Izu-BoninTrench. J. Geophys. Res. Solid Earth 126, e2021JB022132 (2021). doi:10.1029/2021JB022132
S. M. Varlamov, X. Guo, T. Miyama, K. Ichikawa, T. Waseda, Y. Miyazawa. M2 baroclinic tide variability modulated by the ocean circulation south of Japan. J. Geophys. Res. Oceans 120, 3681-3720 (2015). doi:10.1002/2015JC010739
Figure captions:
Fig.1. Residual (Original-Reference) records at the 8 stations of the array during the 34 days period from 2015-07-24, 17:06:40. Two pressure drop events correspond to Typhoon 201514 and Typhoon 201516.
Fig.2. Track of the central pressure drop of Typhoon 201514 (Molave) (http://agora.ex.nii.ac.jp/digital-typhoon/summary/wnp/s/201514.html.en). The arrow shows the array location.
Fig.3. The array configuration on the deep seafloor to the west of the Izu-Bonin Trench. Typhoon 201514 passed through the eastern part of the array. The pathway of the typhoon is shown by blue diamond containing information about air pressure (hPa) at time (day and hour).