Dynamics of Atmospheres and Oceans 78 (2017) 26–37 Contents lists available at ScienceDirect Dynamics of Atmospheres and Oceans journal homepage: www.elsevier.com/locate/dynatmoce Interannual spring Wyrtki jet variability and its regional impacts Aditi Deshpande a,b , C. Gnanaseelan a,∗ , J.S. Chowdary a , S. Rahul a,c a Indian Institute of Tropical Meteorology, Pune, 411008, India b Savitribai Phule Pune University, Pune, 411007, India c Centre for Global Sea Level Change, New York University, Abu Dhabi, 129188, United Arab Emirates a r t i c l e i n f o Article history: Received 4 November 2016 Received in revised form 5 February 2017 Accepted 13 February 2017 Available online 17 February 2017 Keywords: Wyrtki jets Intraseasonal variability Interannual variability Climate variability Indian monsoon a b s t r a c t The role of spring Wyrtki jets in modulating the equatorial Indian Ocean and the regional climate is an unexplored problem. The source of interannual variability in the spring Wyrtki jets is explored in this study. The relationship between intraseasonal and interannual variability from 1958 to 2008 and its relation with Indian Summer Monsoon is further addressed. Analysis reveals that the interannual variability in spring Wyrtki jets is con- trolled significantly by their intraseasonal variations. These are mostly defined by a single intraseasonal event of duration 20 days or more which either strengthens or weakens the seasonal mean jet depending on its phase. The strong spring jets are driven by such intrasea- sonal westerly wind bursts lasting for 20-days or more, whereas the weak jets are driven by weaker intraseasonal westerlies. During the years of strong jets, the conventional west- ward phase propagation of Wyrtki jets is absent and instead there is an eastward phase propagation indicating the possible role of Madden Julian Oscillation (MJO) in strengthen- ing the spring Wyrtki jets. These strong intraseasonal westerly wind bursts with eastward phase propagation during strong years are observed mainly in late spring and have impli- cations on June precipitation over the Indian and adjoining land mass. Anomalously strong eastward jets accumulate warm water in the eastern equatorial Indian Ocean (EIO), leading to anomalous positive upper ocean heat content and supporting more local convection in the east. This induces subsidence over the Indian landmass and alters monsoon rainfall by modulating monsoon Hadley circulation. In case of weak current years such warm anoma- lies are absent over the eastern EIO. Variations in the jet strength are found to have strong impact on sea level anomalies, heat content, salinity and sea surface temperature over the equatorial and north Indian Ocean making it a potentially important player in the north Indian Ocean climate variability. © 2017 Elsevier B.V. All rights reserved. 1. Introduction The occurrence of the unique Equatorial Jets in the Indian Ocean were discovered in the monthly maps of circulation by Wyrtki (Wyrtki, 1973) and have since been rechristened as Wyrtki jets. However, the role of the equatorial Indian Ocean (EIO, 40 ◦ E–110 ◦ E, 2 ◦ S–2 ◦ N) and these jets in modulating regional climate is not well defined to date. During the monsoon ∗ Corresponding author. E-mail address: seelan@tropmet.res.in (C. Gnanaseelan). http://dx.doi.org/10.1016/j.dynatmoce.2017.02.001 0377-0265/© 2017 Elsevier B.V. All rights reserved.