Effect of late 1970's climate shift on tropospheric biennial oscillation—role of local Indian Ocean processes on Asian summer monsoon

Abstract

ABSTRACT:The tropical climate has undergone noticeable changes on interdecadal time scales. The climate shift that occurred in the late 1970s attained enormous attention owing to its global-scale variations in ocean temperature, heat content and El Nino Southern Oscillation (ENSO) properties. Earlier studies presented the effect of this shift on ENSO and the Asian summer monsoon-ENSO relationship. The present study is an attempt to investigate the effect of late 1970's climate shift on tropospheric biennial oscillation (TBO), which is an important tropical phenomenon that includes both air-sea processes in the tropical Indian and Pacific Ocean regions. TBO is the tendency for the Asian-Australian monsoon system to alternate between relatively strong and weak years. The study comprises a detailed analysis of the TBO cycle in the time periods before and after ) the climate shift in 1976 with the help of National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) data sets of 200-hPa velocity potential; the Indian Ocean sea surface temperature (SST) and circulation are more obvious after the shift, although they were significant in the Pacific Ocean before 1976. The effect of ENSO in the biennial cycle is reduced with climate shift. The persistence of Asian-to-Australian summer monsoon has weakened in recent decades, as it is controlled by ENSO. Local oceanic processes in the Indian Ocean and local monsoon Hadley circulation have an increased role in the biennial oscillation of the Asian summer monsoon after 1976.

Temporal Variability of Annual Rainfall in the Macta and Tafna Catchments, Northwestern Algeria

“…The variation may not be attributed to rainfall measurement error since, in many areas of the world, a significant change in general atmospheric circulation was observed during that decade (e.g. Ivanov and Evtimov 2009;Pillai and Mohankumar 2010;Trenberth and Hurrell 1994;Wang et al 2010). For instance, according to Wang et al (2010), "in the mid-1970s, the atmospheric circulation underwent significant changes in many regions of the world".…”

“…This change in general atmospheric circulation affected the variability of climate indices and of hydroclimatic variables (temperature, precipitation, wind, streamflow, etc.). As for the tropical region, Pillai and Mohankumar (2010) noted that "the tropical climate system has undergone many secular changes on interdecadal timescales as the climate shift occurred in 1976. Along with the shift, a significant increase in sea surface temperature was found in the tropical central and eastern Pacific and Indian Ocean".…”

Multi‐index characterization of compound dry hot events in India

“…Therefore, analysing the CDHE events using the CDHE indices will help quantify CDHE severities in India as well which is lacking in the literature. Past studies have reported on the role of large‐scale circulation patterns like ENSO, PDO, Equatorial Indian Ocean Monsoon Oscillation (EQUINOO), and Indian Ocean Dipole (IOD) in modulating temperature and precipitation‐based events in India (Murari et al, 2016; Pattanayak et al, 2017; Pillai & Mohankumar, 2010). However, no studies in the past have reported how large‐scale climate patterns such as ENSO, PDO, EQUINOO and IOD influence CDHEs in India.…”

Weakening of the biennial relationship between Central American and equatorial South American rainfall in recent decades

“…Prominent decadal variation has been observed in the biennial rainfall relationship over the tropical eastern hemisphere (e.g. Ashok et al 2014;Meehl and Arblaster 2011;Pillai and Mohankumar 2010;Wu 2016). However, it remains necessary to determine if there are significant decal changes in the biennial rainfall relationship between CA and ESA over the tropical western hemisphere.…”