Enhanced winter and summer trend difference of Madden–Julian Oscillation intensity since 1871

Abstract

Long-term winter and summer Madden-Julian Oscillation (MJO) trends in the past 138 years (1871-2008) were examined using National Oceanic and Atmospheric Administration (NOAA) 20th Century Reanalysis V2c dataset. It is found that MJO shows a distinctive different trend between boreal winter and summer. While the MJO intensity in both boreal winter and summer has a rising trend, the winter trend is much greater than the summer trend. As a result, the winter-summer difference shows a significant increasing trend. The distinctive winter and summer trends are attributed to the difference of atmospheric background circulation (such as vertical velocity) and static stability responses to the global warming between boreal winter and summer over equatorial eastern Indian Ocean. In boreal winter, both the surface moistening and strengthened inter-tropical convergence zone convection contribute to an increase of MJO activity. This is in contrast to boreal summer when a greater static stability and anomalous subsidence tend to offset the moistening effect, leading to a relatively weaker increase of the MJO activity.

Interdecadal variability of intensity of the Madden–Julian oscillation

“…The interdecadal variability of the MJO intensity was investigated based on two century-long reanalysis datasets (20CR and ERA-20C). The two datasets were capable of capturing the amplitude, structure and evolution characteristics of the MJO through a comparison with the observed features during the period of 1979-2008 (Wang et al, 2020). The DJF-mean daily RMM indices were used to represent the MJO intensity each year.…”

“…The intensity of MJO displays a strong seasonality (Madden, 1986;Wang and Rui, 1990;Zhang and Dong, 2004), an interannual variability (Salby et al, 1994;Slingo et al, 1999;Kessler, 2001;Chen et al, 2016;Yoo and Son, 2016) and a trend (e.g., Slingo et al, 1999;Zveryaev, 2002;Jones and Carvalho, 2006;Tao et al, 2015;Wang et al, 2020). For example, while the MJO is dominated by eastward propagation in boreal winter, the boreal summer intraseasonal oscillation exhibits pronounced northward propagation (Jiang et al, 2004).…”

“…Slingo et al (1999) and Jones and Carvalho (2006) found that MJO appeared more active after 1976. Using century-long reanalysis datasets, Wang et al (2020) noted that the boreal winter MJO intensity increases at a much greater rate than the boreal summer counterpart.…”

Modulation of the intraseasonal variability in early summer precipitation in eastern China by the Quasi-Biennial Oscillation and the Madden–Julian Oscillation

“…The strength of the MJO varies with the season, which is more evident in boreal winter but much weaker in boreal summer (Lafleur et al, 2015;Lu and Hsu, 2017). This difference may be attributed to the surface moistening and strengthened convection in the Intertropical Convergence Zone (ITCZ) in boreal winter, differing from larger static stability and strengthened sinking motion in boreal summer (Wang et al, 2020). This nonuniformity with the season is also identified for the relationship between the Quasi-Biennial Oscillation (QBO) and the MJO, with the MJO-QBO teleconnection getting maximized in boreal winter (Toms et al, 2020;Martin et al, 2021).…”