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The role of the SST-thermocline relationship in Indian Ocean Dipole skewness and its response to global warming.

Ng B, Cai W, Walsh K - Sci Rep (2014)

Bottom Line: This asymmetric thermocline feedback drives IOD skewness despite positive IODs receiving greater damping from the SCR feedback.In response to global warming, although the thermocline feedback strengthens, its asymmetry between positive and negative IODs weakens.This behaviour change explains the reduction in IOD skewness that many models display under global warming.

View Article: PubMed Central - PubMed

Affiliation: 1] CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia [2] School of Earth Sciences, University of Melbourne, Parkville, Victoria, Australia.

ABSTRACT
A positive Indian Ocean Dipole (IOD) tends to have stronger cold sea surface temperature anomalies (SSTAs) over the eastern Indian Ocean with greater impacts than warm SSTAs that occur during its negative phase. Two feedbacks have been suggested as the cause of positive IOD skewness, a positive Bjerknes feedback and a negative SST-cloud-radiation (SCR) feedback, but their relative importance is debated. Using inter-model statistics, we show that the most important process for IOD skewness is an asymmetry in the thermocline feedback, whereby SSTAs respond to thermocline depth anomalies more strongly during the positive phase than negative phase. This asymmetric thermocline feedback drives IOD skewness despite positive IODs receiving greater damping from the SCR feedback. In response to global warming, although the thermocline feedback strengthens, its asymmetry between positive and negative IODs weakens. This behaviour change explains the reduction in IOD skewness that many models display under global warming.

No MeSH data available.


Related in: MedlinePlus

Relationship between change in IODE SST skewness and the change in thermocline feedback asymmetry.SON IODE SST skewness change (RCP8.5 minus historical) versus the change in slope difference (asymmetry) for the thermocline feedback. The slope difference is defined as the pIOD linear regression coefficient minus the nIOD linear regression coefficient. Linear correlation, regression and p values are indicated in the bottom left hand corner. All plots were generated in NCL.
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f3: Relationship between change in IODE SST skewness and the change in thermocline feedback asymmetry.SON IODE SST skewness change (RCP8.5 minus historical) versus the change in slope difference (asymmetry) for the thermocline feedback. The slope difference is defined as the pIOD linear regression coefficient minus the nIOD linear regression coefficient. Linear correlation, regression and p values are indicated in the bottom left hand corner. All plots were generated in NCL.

Mentions: Under increasing greenhouse gases, the SST skewness response to the slope difference becomes slightly stronger (Fig. 2d). This behaviour indicates that under global warming, the thermocline feedback strengthens and thus it has a stronger influence on SST skewness. Similar to the historical period, the linear correlation coefficient is also significant at the 95% confidence level. These figures show that the thermocline feedback plays an important role in the modelled SST skewness in both the historical and RCP8.5 periods. However, Fig. 2d does not indicate how the thermocline feedback has changed under global warming, or how this impacts its role in generating IOD skewness. To examine this, the difference between RCP8.5 and historical simulations is plotted for both IODE SST skewness and the slopes of the thermocline feedback (Fig. 3). Most of the models show a negative change in slope difference, indicating that the RCP8.5 slope difference between positive and negative IODs is less than the historical value. For these models, the asymmetry of the thermocline feedback is decreasing. From this, it is clear that there is a strong relationship between IOD skewness and the asymmetry of the thermocline feedback. Figure 3 also shows that the majority of models (14) simulate a weakening in IODE SST skewness in response to global warming. This relationship between the change in skewness and the change in slope difference is significant at the 95% confidence level.


The role of the SST-thermocline relationship in Indian Ocean Dipole skewness and its response to global warming.

Ng B, Cai W, Walsh K - Sci Rep (2014)

Relationship between change in IODE SST skewness and the change in thermocline feedback asymmetry.SON IODE SST skewness change (RCP8.5 minus historical) versus the change in slope difference (asymmetry) for the thermocline feedback. The slope difference is defined as the pIOD linear regression coefficient minus the nIOD linear regression coefficient. Linear correlation, regression and p values are indicated in the bottom left hand corner. All plots were generated in NCL.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4129411&req=5

f3: Relationship between change in IODE SST skewness and the change in thermocline feedback asymmetry.SON IODE SST skewness change (RCP8.5 minus historical) versus the change in slope difference (asymmetry) for the thermocline feedback. The slope difference is defined as the pIOD linear regression coefficient minus the nIOD linear regression coefficient. Linear correlation, regression and p values are indicated in the bottom left hand corner. All plots were generated in NCL.
Mentions: Under increasing greenhouse gases, the SST skewness response to the slope difference becomes slightly stronger (Fig. 2d). This behaviour indicates that under global warming, the thermocline feedback strengthens and thus it has a stronger influence on SST skewness. Similar to the historical period, the linear correlation coefficient is also significant at the 95% confidence level. These figures show that the thermocline feedback plays an important role in the modelled SST skewness in both the historical and RCP8.5 periods. However, Fig. 2d does not indicate how the thermocline feedback has changed under global warming, or how this impacts its role in generating IOD skewness. To examine this, the difference between RCP8.5 and historical simulations is plotted for both IODE SST skewness and the slopes of the thermocline feedback (Fig. 3). Most of the models show a negative change in slope difference, indicating that the RCP8.5 slope difference between positive and negative IODs is less than the historical value. For these models, the asymmetry of the thermocline feedback is decreasing. From this, it is clear that there is a strong relationship between IOD skewness and the asymmetry of the thermocline feedback. Figure 3 also shows that the majority of models (14) simulate a weakening in IODE SST skewness in response to global warming. This relationship between the change in skewness and the change in slope difference is significant at the 95% confidence level.

Bottom Line: This asymmetric thermocline feedback drives IOD skewness despite positive IODs receiving greater damping from the SCR feedback.In response to global warming, although the thermocline feedback strengthens, its asymmetry between positive and negative IODs weakens.This behaviour change explains the reduction in IOD skewness that many models display under global warming.

View Article: PubMed Central - PubMed

Affiliation: 1] CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia [2] School of Earth Sciences, University of Melbourne, Parkville, Victoria, Australia.

ABSTRACT
A positive Indian Ocean Dipole (IOD) tends to have stronger cold sea surface temperature anomalies (SSTAs) over the eastern Indian Ocean with greater impacts than warm SSTAs that occur during its negative phase. Two feedbacks have been suggested as the cause of positive IOD skewness, a positive Bjerknes feedback and a negative SST-cloud-radiation (SCR) feedback, but their relative importance is debated. Using inter-model statistics, we show that the most important process for IOD skewness is an asymmetry in the thermocline feedback, whereby SSTAs respond to thermocline depth anomalies more strongly during the positive phase than negative phase. This asymmetric thermocline feedback drives IOD skewness despite positive IODs receiving greater damping from the SCR feedback. In response to global warming, although the thermocline feedback strengthens, its asymmetry between positive and negative IODs weakens. This behaviour change explains the reduction in IOD skewness that many models display under global warming.

No MeSH data available.


Related in: MedlinePlus