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Combined effects of recent Pacific cooling and Indian Ocean warming on the Asian monsoon.

Ueda H, Kamae Y, Hayasaki M, Kitoh A, Watanabe S, Miki Y, Kumai A - Nat Commun (2015)

Bottom Line: During the hiatus, the tropical Pacific Ocean displays a La Niña-like cooling pattern while sea surface temperature (SST) in the Indian Ocean has continued to increase.This SST pattern differs from the well-known La Niña-induced basin-wide cooling across the Indian Ocean on the interannual timescale.Overall, the tropical Pacific SST effect opposes and is greater than the Indian Ocean SST effect.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan.

ABSTRACT
Recent research indicates that the cooling trend in the tropical Pacific Ocean over the past 15 years underlies the contemporaneous hiatus in global mean temperature increase. During the hiatus, the tropical Pacific Ocean displays a La Niña-like cooling pattern while sea surface temperature (SST) in the Indian Ocean has continued to increase. This SST pattern differs from the well-known La Niña-induced basin-wide cooling across the Indian Ocean on the interannual timescale. Here, based on model experiments, we show that the SST pattern during the hiatus explains pronounced regional anomalies of rainfall in the Asian monsoon region and thermodynamic effects due to specific humidity change are secondary. Specifically, Indo-Pacific SST anomalies cause convection to intensify over the tropical western Pacific, which in turn suppresses rainfall in mid-latitude East Asia through atmospheric teleconnection. Overall, the tropical Pacific SST effect opposes and is greater than the Indian Ocean SST effect.

No MeSH data available.


Related in: MedlinePlus

Vertically integrated moisture budget incorporating tropical Pacific and Indian Ocean effects.(a) Dynamic effect (dDY), thermodynamic effect (dTH), horizontal advection (dHAD) and evaporation (dE) averaged over the WP region against for the net precipitation change (dP) based on 10-ensemble experiments. (b) As in a, but for the WIO region. (c) As in a, but for the EA region; see Methods. Note that the vertical scale of c is half that of a,b. The 5% significant level obtained from the Student's t-test is denoted by error bars.
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f4: Vertically integrated moisture budget incorporating tropical Pacific and Indian Ocean effects.(a) Dynamic effect (dDY), thermodynamic effect (dTH), horizontal advection (dHAD) and evaporation (dE) averaged over the WP region against for the net precipitation change (dP) based on 10-ensemble experiments. (b) As in a, but for the WIO region. (c) As in a, but for the EA region; see Methods. Note that the vertical scale of c is half that of a,b. The 5% significant level obtained from the Student's t-test is denoted by error bars.

Mentions: The spatial distributions of decreased/increased rainfall in Fig. 3 correspond well with downward/upward motion (Supplementary Fig. 4), indicating an importance of dynamic effect on the rainfall change. Therefore, to improve our quantitative understanding of the rainfall variation, we calculated vertically integrated moisture budgets12 (see Methods) and decomposed the dynamic and thermodynamic processes associated with the rainfall variations over the three regions (Fig. 4). Note that linear additivity does not hold because we do not consider effects from the extratropics. However, as shown in Table 1, the TPO and IO effects are dominant players in the total rainfall change. In the WP region (Fig. 4a), the net effect of the full SST anomaly during the hiatus (Full Exp; black bar) is to enhance rainfall, which is associated with the dynamic effect (upward motion) and enhanced evaporation from the sea surface. The rainfall increase is closely related with the tropical Pacific (TPO Exp); however, the subsidence induced by Indian Ocean warming corresponds to the WP rainfall decrease, and this is manifested in a negative dynamic effect in the IO Exp. Over the WIO (Fig. 4b), the full SST effect is almost zero. The rainfall change associated with the Indian Ocean warming is largely offset by the remote influence of dynamic effect originating from the tropical Pacific SST (see also Fig. 3). These results indicate that in both the Indian Ocean and WP the Pacific LNSST anomalies and the Indian Ocean warming tend to oppose each other in the atmospheric moisture budget. In the most cases, rainfall change over the WP in response to the local SST anomaly is larger than those over the Indian Ocean. Over the EA region (Fig. 4c), the negative dynamic effect originating from the LNSST anomalies in the tropical Pacific is associated with the net decrease in rainfall despite increased evaporation in the WP. The effect of Indian Ocean on EA is small. This is consistent with the position of anomalous anticyclone (Fig. 3b), dominating to the south of EA region. S.d. among 10 members (Table 1) is large in the EA region, indicating an importance of internal climate variability over the mid-latitude. Significant model biases found in Full Exp (for example, large positive rainfall in 110°E, 40°N that is not found in the observation) contribute to decrease the area-averaged rainfall anomalies. However, most of water budget components including dP except WIO rainfall in Full Exp and EA rainfall in IO Exp are statistically significant at 95% confidence level in the three key regions.


Combined effects of recent Pacific cooling and Indian Ocean warming on the Asian monsoon.

Ueda H, Kamae Y, Hayasaki M, Kitoh A, Watanabe S, Miki Y, Kumai A - Nat Commun (2015)

Vertically integrated moisture budget incorporating tropical Pacific and Indian Ocean effects.(a) Dynamic effect (dDY), thermodynamic effect (dTH), horizontal advection (dHAD) and evaporation (dE) averaged over the WP region against for the net precipitation change (dP) based on 10-ensemble experiments. (b) As in a, but for the WIO region. (c) As in a, but for the EA region; see Methods. Note that the vertical scale of c is half that of a,b. The 5% significant level obtained from the Student's t-test is denoted by error bars.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4660201&req=5

f4: Vertically integrated moisture budget incorporating tropical Pacific and Indian Ocean effects.(a) Dynamic effect (dDY), thermodynamic effect (dTH), horizontal advection (dHAD) and evaporation (dE) averaged over the WP region against for the net precipitation change (dP) based on 10-ensemble experiments. (b) As in a, but for the WIO region. (c) As in a, but for the EA region; see Methods. Note that the vertical scale of c is half that of a,b. The 5% significant level obtained from the Student's t-test is denoted by error bars.
Mentions: The spatial distributions of decreased/increased rainfall in Fig. 3 correspond well with downward/upward motion (Supplementary Fig. 4), indicating an importance of dynamic effect on the rainfall change. Therefore, to improve our quantitative understanding of the rainfall variation, we calculated vertically integrated moisture budgets12 (see Methods) and decomposed the dynamic and thermodynamic processes associated with the rainfall variations over the three regions (Fig. 4). Note that linear additivity does not hold because we do not consider effects from the extratropics. However, as shown in Table 1, the TPO and IO effects are dominant players in the total rainfall change. In the WP region (Fig. 4a), the net effect of the full SST anomaly during the hiatus (Full Exp; black bar) is to enhance rainfall, which is associated with the dynamic effect (upward motion) and enhanced evaporation from the sea surface. The rainfall increase is closely related with the tropical Pacific (TPO Exp); however, the subsidence induced by Indian Ocean warming corresponds to the WP rainfall decrease, and this is manifested in a negative dynamic effect in the IO Exp. Over the WIO (Fig. 4b), the full SST effect is almost zero. The rainfall change associated with the Indian Ocean warming is largely offset by the remote influence of dynamic effect originating from the tropical Pacific SST (see also Fig. 3). These results indicate that in both the Indian Ocean and WP the Pacific LNSST anomalies and the Indian Ocean warming tend to oppose each other in the atmospheric moisture budget. In the most cases, rainfall change over the WP in response to the local SST anomaly is larger than those over the Indian Ocean. Over the EA region (Fig. 4c), the negative dynamic effect originating from the LNSST anomalies in the tropical Pacific is associated with the net decrease in rainfall despite increased evaporation in the WP. The effect of Indian Ocean on EA is small. This is consistent with the position of anomalous anticyclone (Fig. 3b), dominating to the south of EA region. S.d. among 10 members (Table 1) is large in the EA region, indicating an importance of internal climate variability over the mid-latitude. Significant model biases found in Full Exp (for example, large positive rainfall in 110°E, 40°N that is not found in the observation) contribute to decrease the area-averaged rainfall anomalies. However, most of water budget components including dP except WIO rainfall in Full Exp and EA rainfall in IO Exp are statistically significant at 95% confidence level in the three key regions.

Bottom Line: During the hiatus, the tropical Pacific Ocean displays a La Niña-like cooling pattern while sea surface temperature (SST) in the Indian Ocean has continued to increase.This SST pattern differs from the well-known La Niña-induced basin-wide cooling across the Indian Ocean on the interannual timescale.Overall, the tropical Pacific SST effect opposes and is greater than the Indian Ocean SST effect.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan.

ABSTRACT
Recent research indicates that the cooling trend in the tropical Pacific Ocean over the past 15 years underlies the contemporaneous hiatus in global mean temperature increase. During the hiatus, the tropical Pacific Ocean displays a La Niña-like cooling pattern while sea surface temperature (SST) in the Indian Ocean has continued to increase. This SST pattern differs from the well-known La Niña-induced basin-wide cooling across the Indian Ocean on the interannual timescale. Here, based on model experiments, we show that the SST pattern during the hiatus explains pronounced regional anomalies of rainfall in the Asian monsoon region and thermodynamic effects due to specific humidity change are secondary. Specifically, Indo-Pacific SST anomalies cause convection to intensify over the tropical western Pacific, which in turn suppresses rainfall in mid-latitude East Asia through atmospheric teleconnection. Overall, the tropical Pacific SST effect opposes and is greater than the Indian Ocean SST effect.

No MeSH data available.


Related in: MedlinePlus