Recent abnormal changes in wintertime atmospheric response to tropical SST forcing

Kawamura, Ryuichi; Sugi, Masato; Kayahara, Takahiro; Sato, Nobuo

doi:10.1029/97gl00688

Cited by 10 publications

(2 citation statements)

References 24 publications

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“…Very significant negative anomalies cover the entire tropics. A north‐south dipole structure of the geopotential height anomalies over the central tropical Pacific is a typical signature of the upper tropospheric response to ENSO [e.g., Kumar et al , 1996; Kawamura et al , 1997; Lau and Nath , 2000]. In a similar fashion, Figure 6b shows the composite differences in OLR and the 200‐hPa velocity potential.…”

Section: Dominant Patterns Of the Asian Jet Variability Over South Asiamentioning

confidence: 79%

Remote response of the East Asian winter monsoon to tropical forcing related to El Niño–Southern Oscillation

Sakai¹,

Kawamura²

2009

J. Geophys. Res.

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[1] The mechanism of the East Asian winter monsoon variability in response to El NiñoÀSouthern Oscillation (ENSO)-related tropical forcing is investigated using Japanese long-term reanalysis project data, additionally aided by the Japan Meteorological Agency climate data assimilation system. There are at least two different responses, zonally symmetric and asymmetric, of the Asian jet over South Asia to the ENSO-related tropical convective forcing during the Northern Hemisphere winter. The zonally symmetric response, induced by zonally extended anomalous convection from the Philippine Sea through southern India and Sri Lanka, is pronounced at the mature phase of ENSO. The zonally asymmetric response is intimately associated with anomalous convection localized in the vicinity of the Philippine and South China seas, accompanied by an anomalous Walker circulation cell between the Maritime Continent and tropical Indian Ocean. When this asymmetric response is prominent, ENSO-related anomalous convection can give rise to a change in the East Asian winter monsoon system through stationary Rossby wave propagation along the South Asian waveguide. The North Atlantic Oscillation (NAO)-related extratropical forcing is also a crucial factor and contributes not only to the downstream development of subpolar teleconnections across northern Eurasia but also to the reinforcement of the zonally asymmetric pattern of the Asian jet over South Asia, resulting in a significant effect on the East Asian winter monsoon circulation. A combination of the ENSO-and NAO-related forcing plays a vital role in triggering the occurrence of extraordinary anomalous monsoon circulations, such as extremely heavy snowfall in the 2005/2006 winter in Japan.Citation: Sakai, K., and R. Kawamura (2009), Remote response of the East Asian winter monsoon to tropical forcing related to El Niño -Southern Oscillation,

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Section: Dominant Patterns Of the Asian Jet Variability Over South Asiamentioning

confidence: 79%

Remote response of the East Asian winter monsoon to tropical forcing related to El Niño–Southern Oscillation

Sakai¹,

Kawamura²

2009

J. Geophys. Res.

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“…Also, unlike in the Pacific, the Atlantic equatorial cold tongue is centered south of the equator and how equatorial waves influence this region may be different. Other possible mechanisms include, the western Pacific oscillator [Weisberg and Wang, 1997], advective-reflective oscillator [Picaut et al, 1997;Wang, 2001], or a destabilized basin mode [Jin and Neelin, 1993;.The western Pacific oscillator, however, is probably not active in the Atlantic, as no negative SST or westward wind stress anomalies exist in the western Atlantic during the zonal mode's peak phase (Figure 1b). Zonal current variations are important in both the advective-reflective oscillator and destabilized basin-mode mechanisms.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

Equatorial Atlantic interannual variability: Role of heat content

2010

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[1] The dynamics of the equatorial Atlantic zonal mode are studied using observed sea surface height (SSH), sea surface temperature (SST), and heat flux and reanalysis wind stress and upper ocean temperature. Principal oscillation pattern (POP) analysis shows that the zonal mode is an oscillatory normal mode of the observed coupled system, obeying the delayed action/recharge oscillator paradigm for El Niño Southern Oscillation. Variations in equatorial averaged SSH, a proxy for upper ocean heat content, precede SST anomalies in the cold tongue by 4-5 months, about a quarter of the POP period. Positive subsurface temperature anomalies appear in the west, as a delayed response to the preceding cold event. These propagate eastward, where due to the shallow thermocline they can influence SST, leading to the next warm event. Although SST variations exhibit weak westward propagation during some zonal mode events, POP analysis indicates that to first order there is no zonal propagation in SST. Net surface heat flux anomalies generally act to damp SST anomalies. The zonal mode explains a large amount (70%) of SST variability in the east and a significant fraction (19%) of equatorial variability. Thus, the predictability potential in the equatorial Atlantic on seasonal time scales may be considerably higher than currently thought.

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The impact of mean state errors on equatorial Atlantic interannual variability in a climate model

et al. 2015

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Observations show that the Equatorial Atlantic Zonal Mode (ZM) obeys similar physics to the El Niño Southern Oscillation (ENSO): positive Bjerknes and delayed negative feedbacks. This implies the ZM may be predictable on seasonal timescales, but models demonstrate little prediction skill in this region. In this study using different configurations of the Kiel Climate Model (KCM) exhibiting different levels of systematic error, we show that a reasonable simulation of the ZM depends on realistic representation of the mean state, i.e., surface easterlies along the equator, upward sloping thermocline to the east, with an equatorial SST cold tongue in the east. We further attribute the differences in interannual variability among the simulations to the individual components of the positive Bjerknes and delayed negative feedbacks. Differences in the seasonality of the variability are similarly related to the impact of seasonal biases on the Bjerknes feedback. Our results suggest that model physics must be enhanced to enable skillful seasonal predictions in the Tropical Atlantic Sector, although some improvement with regard to the simulation of Equatorial Atlantic interannual variability may be achieved by momentum flux correction. This pertains especially to the seasonal phase locking of interannual SST variability.

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Recent abnormal changes in wintertime atmospheric response to tropical SST forcing

Cited by 10 publications

References 24 publications

Remote response of the East Asian winter monsoon to tropical forcing related to El Niño–Southern Oscillation

Remote response of the East Asian winter monsoon to tropical forcing related to El Niño–Southern Oscillation

Equatorial Atlantic interannual variability: Role of heat content

The impact of mean state errors on equatorial Atlantic interannual variability in a climate model

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