Subseasonal variations in spatial signatures of ENSO on the Indian summer monsoon from 1901 to 2009

Abstract

Correlations of 1 ∘ by 1 ∘ seasonal rainfall with Pacific sea surface temperatures (SSTs) reveal spatially distinct teleconnections between El Niño-Southern Oscillation (ENSO) and Indian summer monsoon rainfall over the full monsoon season, as well as three subseasons. Over the full season (June-September), Pacific SSTs correlate with rainfall in Western India more than that in Eastern India. This spatial signature shifts as the monsoon progresses through early (June), middle or peak (July-August), and late (September) subseasons. Specifically, a 1 ∘ C cooling of the central equatorial Pacific (i.e., La Niña conditions) can result in the following: ∼70-100% increase in precipitation in north central Indian and the Indo-Gangetic Plains during the early season, ∼30-80% increase peak season precipitation in south central India and northwestern Rajasthan, and ∼60-100% increase in late season precipitation in northern, northwestern, and central India. Furthermore, the spatial signatures between La Niña and El Niño are asymmetric in that for a particular location, the enhancement and suppression of rainfall associated with La Niña and El Niño conditions, respectively, are not equal. El Niño suppresses peak season rainfall in the south central and northwestern Rajasthan regions more than La Niña enhances it, but the opposite occurs during the late season in northern, northwestern, and central India. Additionally, the correspondence of minima (maxima) in anomalies of velocity potential aloft with maxima (minima) at 925 mb and with positive (negative) surface pressure anomalies suggests that anomalous subsidence (ascent) occurs in July-September during El Niño (La Niña) times. In the early season, however, patterns of velocity potential composites suggest a region of descent (ascent) over the western equatorial Indian Ocean, along with a region of ascent (descent) over the Indian subcontinent that exists only during the early season but not during the peak or late season. These patterns are consistent with the hypothesis that local Hadley cell circulation affects pressure and thus rainfall during the early season but that a larger-scale mechanism, such as eastward or westward shifts in the Walker circulation, may be more responsible for teleconnections seen throughout the remainder of the season. These findings indicate that focusing monsoon forecasting efforts on these regions and on subseasonal periods while incorporating ENSO asymmetries will yield useful and skillful regional forecasts, compared to the declining utility and skill of all-India summer monsoon rainfall.

Simulation of the Central Indian Ocean Mode in CESM: Implications for the Indian Summer Monsoon System

“…In addition, the monsoon system is a critical component in the “seamless” multiscale climate system. The relations between the Indian summer monsoon and major climate modes (such as ENSO and IODZM) are still being debated (Ashok et al, ; Gill et al, ; Kumar et al, ; Sabeerali et al, ). The CIO mode, as a climate mode mainly at intraseasonal timescales and with pronounced seasonal and interannual variabilities, provides a new avenue to pinpoint the role of the Indian Ocean and the Indian summer monsoon in the climate system and helps to reveal the relationship between the Indian summer monsoon and other climate processes.…”

“…In addition, a better understanding of MISO also has an obvious scientific and socioeconomic significance for the livelihood of billions of people living on the rim of the Indian Ocean. To date, the predictability of monsoon rainfall remains low (Wang et al, ), which is attributable to the much‐debated relationship between MISO and the major intrinsic climate modes, such as ENSO (e.g., Gill et al, ; Kumar et al, ) and the Indian Ocean Dipole‐Zonal Mode (IODZM) (e.g., Ashok et al, ; Kripalani & Kumar, ; Murtugudde & Busalacchi, ; Murtugudde et al, ). Recently, a central Indian Ocean (CIO) mode, which is defined using a combination of intraseasonal sea surface temperature (SST) anomalies and intraseasonal low‐level wind anomalies over the Indian Ocean, was found to have a close relation with monsoonal rainfall (Zhou et al, ).…”

Climate–Glacier Dynamics and Topographic Forcing in the Karakoram Himalaya: Concepts, Issues and Research Directions

“…Weakening of the Indian summer monsoon produces less precipitation and droughts whereas the stronger La Niña monsoon produces enhanced precipitation [92,93]. The observed correlation between ENSO and the monsoon does not, however, guarantee a weakening of the Indian summer monsoon during an El Niño event due to the statistical nature of the relationship [80,93,94]. Elucidating a clearer understanding of the dynamical relationship between ENSO and the monsoon is important, as it is one of the important factors governing precipitation over the glaciers in the Karakoram Himalaya.…”

Teleconnections between ENSO and rainfall and drought in Puerto Rico

“…In an area with a strong ENSO teleconnection, Gill et al . () found notable teleconnection asymmetries implying important variations in signal strength and direction by region and sub‐seasons. In other words, detecting a strong ENSO warm episode does not imply that its opposite phase (ENSO cool episode) will occur with the same intensity, at the same region or in the same season.…”

“…Yet, assuming the same level of teleconnection at each and every place on Earth would also be misleading, because the ENSO signal varies in magnitude and direction at different spatial and temporal scales. In an area with a strong ENSO teleconnection, Gill et al (2015) found notable teleconnection asymmetries implying important variations in signal strength and direction by region and sub-seasons. In other words, detecting a strong ENSO warm episode does not imply that its opposite phase (ENSO cool episode) will occur with the same intensity, at the same region or in the same season.…”