Variability of upper ocean thermohaline structure during a MJO event from DYNAMO aircraft observations

• Published in: Journal of geophysical research. Oceans 2017-02, Vol.122 (2), p.1122-1140
• Main Authors: Alappattu, Denny P., Wang, Qing, Kalogiros, John, Guy, Nick, Jorgensen, David P.
• Format: Article
• Language: English
• Subjects: Airborne sensing; Aircraft; Aircraft components; Aircraft observations; Barrier layers; Columns (structural); Distribution; Dynamics; DYNAMO; Equator; Geophysics; Heterogeneity; Indian Ocean; Indonesian Throughflow; Intrusion; Isothermal layers; Life cycle; Life cycle engineering; Life cycles; Madden Julian Oscillation; Marine; Meteorological aircraft; Mixed layer; Mixed layer depth; Modes; Ocean circulation; Ocean currents; Oceanography; Oceans; Patchiness; Perturbation methods; Phases; Probes; Saline water; Sensors; Spatial distribution; Spatial heterogeneity; Statistical analysis; Statistical methods; Thermocline; Thermoclines; Thermohaline structure; Thermohalines; Tropical climate; Upper ocean; Variability; Water column
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1002/2016JC012137

This paper reports upper ocean thermohaline structure and variability observed during the life cycle of an intense Madden Julian Oscillation (MJO) event occurred in the southern tropical Indian Ocean (14°S–Eq, 70°E–81°E). Water column measurements for this study were collected using airborne expendable probes deployed from NOAA's WP‐3D Orion aircraft operated as a part of Dynamics of MJO field experiment conducted during November–December 2011. Purpose of the study is twofold; (1) to provide a statistical analysis of the upper ocean properties observed during different phases of MJO and, (2) to investigate how the upper ocean thermohaline structure evolved in the study region in response to the MJO induced perturbation. During the active phase of MJO, mixed layer depth (MLD) had a characteristic bimodal distribution. Primary and secondary modes were at ∼34 m and ∼65 m, respectively. Spatial heterogeneity of the upper ocean response to the MJO forcing was the plausible reason for bimodal distribution. Thermocline and isothermal layer depth deepened, respectively, by 13 and 19 m from the suppressed through the restoring phase of MJO. Thicker (>30 m) barrier layers were found to occur more frequently in the active phase of MJO, associated with convective rainfalls. Additionally, the water mass analysis indicated that, in the active phase of this MJO event the subsurface was dominated by Indonesian throughflow, nonetheless intrusion of Arabian Sea high saline water was also noted near the equator. Key Points In situ observations are made from the tropical Indian Ocean using airborne expendable probes deployed from P‐3 Orion aircraft Response of mixed layer, isothermal layer, and thermocline is analyzed with respect to the different phases of MJO in the Indian Ocean In the active phase of MJO, the mixed layer depth showed a bimodal distribution