Air-sea interaction at the edges of the Warm Pool

PIs: Masaki Katsumata (JAMSTEC), Akira Nagano (JAMSTEC), Kunio Yoneyama (JAMSTEC), Iwao Ueki (JAMSTEC), Ken Ando (JAMSTEC), Meghan Cronin (NOAA/PMEL), and Dongxiao Zhang (NOAA/PMEL)

Description

Process studies of air-sea interaction at the northern and eastern edges of the warm pool have been conducted by several institutes. The purpose of the study for the northern edge of the warm pool is to capture the multi-scale structure of the Boreal Summer intraseasonal oscillation (BSISO) through high-resolution in situ observations in both the atmosphere and ocean. According to several observation activities at the northern edge of the warm pool, detailed processes, such as the diurnal cycle, impact of typhoons, etc., has been captured. The northern edge study has been an international effort as part of the Years of the Maritime Continent led by BMKG in Indonesia, NOAA/PMEL in the US and JAMSTEC in Japan. This program began in 2017.

The purpose of the study for the eastern edge of the warm pool is to understand the primary mechanisms maintaining the frontal structure at the eastern edge. Observations by Saildrone and research vessels have been conducted with pre-field modeling studies by JAMSTEC and NOAA from 2018.

Fig. 1: Map of the observation area (platform) for two field campaigns; (a) MR18-04 leg-2 (left) and (b) MR20-E01.

Fig. 1: Map of the observation area (platform) for two field campaigns;
(a) MR18-04 leg-2 (left) and (b) MR20-E01.

These projects were funded by the Indonesian Meteorology, Climatology,  and Geophysics Agency (BMKG), the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and the U.S. National Oceanic and Atmospheric Administration.

Accomplishments

JAMSTEC has conducted field campaigns to evaluate the representativeness of the single-point mooring. The campaigns are focusing on the ocean and atmosphere interaction at the meso scale, by deploying multiple platforms around the research vessel for days. We accomplished two field campaigns in 2018 and 2020. In the pilot study in 2018, we stayed around our (13N, 137E) mooring for 4 days with a newly-deployed buoy and a buoy to be recovered (as in Fig. 1a). In 2020, we stayed around (12N, 135E) for 30 days and deployed a special short-term mooring and three unmanned vehicle “Wave Glider” (as in Fig. 1b). During this campaign, we captured the diurnal cycle of the ocean and atmosphere. In addition, the collaborative dual-Doppler observation with U.S. R/V Thompson during the PISTON field campaign was carried out successfully. Another field campaign to evaluate this concept is planned in 2021.

JAMSTEC conducted intensive observations of the ocean and atmosphere around the eastern part of the warm pool by R/V Mirai (MR20-01) cruise from February 23 to March 27, 2020. After capturing the zonal temperature and salinity gradients along the equator by an underway CTD, the intensive observation has been conducted by the R/V Mirai (~161.0˚E) with two Wave Gliders at the west (~158.0˚E) and east (~162.5˚E) of the sea surface temperature (SST) front from March 9 to 14 (Fig 2). During this campaign, we captured a drastic change in the ocean and atmosphere before and after the generation of the tropical depressions nearby. Additionally, we obtained oceanic and atmospheric structures by CTDO2/LADCP down to the depth of 500 dbar and radiosonde up to a height of 100 hPa.

Fig. 2: SST distribution at 12 March 2020 with positions of the R/V Mirai (0, 161.0˚E)and 2 Wave Gliders (0, 158.0˚E and 0, 162.5˚E)

Fig. 2: SST distribution at 12 March 2020 with positions of the R/V Mirai (0, 161.0˚E)and 2 Wave Gliders (0, 158.0˚E and 0, 162.5˚E)

Lessons Learned

Associated with YMC, the PISTON project by U.S. groups conducted a special field campaign from a research vessel deployed around 12°–17°N, 135°E in August-October 2018. JAMSTEC also conducted an observational cruise in the same region in August 2018, conducting special ocean-atmosphere observations. They both collaborated with each other. In addition to capturing detailed structure of air-sea processes including the diurnal cycle and meso-scale convective activity, dual-Doppler radar observations from shipboard polarimetric radars on the 2 research vessels successfully captured the fine three-dimensional structure of the precipitation systems. In addition to the Saildrone mission in 2018, an observational cruise was conducted in February-March 2020 with detailed air-sea measurements at a SST front in the eastern edge of the warm pool. Detailed air-sea structures at both sides of the front were observed. Analyses of the acquired data by these observations are now ongoing and some part of observational study is continued.

The detailed air-sea interaction processes were captured by the meso-scale network over the open ocean. As an example in Fig. 3, the vital and suppressed diurnal cycle of ocean and atmosphere were clearly captured before and after the generation of tropical depression (at Aug.24), at five platforms (R/V Mirai, a mooring, and three unmanned vehicles).

From the cruise in Feb.-Mar. 2020, the warm water at the west of the eastern edge migrated eastward through the substantial air-sea interaction, as evidenced by the coincidence of sea surface zonal current and wind anomaly directions from March 11 and 12 (Fig. 4) and active heat release from the ocean to the atmosphere. Besides, a Doppler radar installed on the R/V Mirai observed active convection along with the air-sea interaction (Fig. 5). It is suggested that monitoring for short-term variability associated with air-sea interactions need high-frequency multi-parameter observations.

Publications

JAMSTEC, 2018: Cruise Report MR18-04 Leg-2. Available from http://www.godac.jamstec.go.jp/catalog/doc_catalog/e/ .

JAMSTEC, 2020: Cruise Report MR20-E01. Available from http://www.godac.jamstec.go.jp/catalog/doc_catalog/e/ .

JAMSTEC, 2020: Cruise Report MR20-01. Available from http://www.godac.jamstec.go.jp/catalog/doc_catalog/e/ .

Data

The raw data will be archived and opened from the JAMSTEC website. The QC’ed data are available upon request to the chief scientist of each cruise, and will be available in the future at a website currently being developed.

Fig. 3: Time series of air temperature and sea surface temperature observed by three Wave Gliders.

Fig. 3: Time series of air temperature and sea surface temperature observed by three Wave Gliders.

Fig. 5: Percentages of larger echo intensity areas than 10 dB within a 100 km from the R/V Mirai.

Fig. 5: Percentages of larger echo intensity areas than 10 dB within a 100 km from the R/V Mirai.

Fig. 4: Time-depth diagrams of zonal (a) wind and (b) current velocity anomalies from the mean value at each vertical level. Positive value indicates eastward velocity. Eastward Contour intervals of wind and current velocity are 2 m/s and 10 cm/s, respectively.

Fig. 4: Time-depth diagrams of zonal (a) wind and (b) current velocity anomalies from the mean value at each vertical level. Positive value indicates eastward velocity. Eastward Contour intervals of wind and current velocity are 2 m/s and 10 cm/s, respectively.