the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Interdecadal Pacific Oscillation responsible for the linkage of decadal changes in precipitation/moisture in arid central Asia and humid Asian monsoon region during the last millennium
Hongna Xu
Huijun Wang
Abstract. Reconstruction and observational studies imply a potential linkage of moisture/precipitation change in arid central Asia and monsoonal East Asia, in which the evolution of moisture/precipitation in central Asia is out-of-phase with that in northern China, but in-phase with that in southern China. In order to ascertain whether there is a robust linkage between the changes in climate in Asian arid regions and monsoon regions and to elucidate the underlying dynamic mechanisms, we analyzed the Last Millennium Reanalysis dataset and output from the Community Earth System Model-Last Millennium Ensemble (CESM-LME). The results indicate a significant decadal linkage between precipitation changes in central Asia’s arid region and the Asian monsoon region during the last millennium, which is primarily driven by the Interdecadal Pacific Oscillation (IPO). In spring, the positive IPO could enhance westerlies over the Mediterranean Sea and to its east, which could transport more water vapor and cause increased precipitation over central Asia. In summer, the positive IPO is accompanied with weakened Asian monsoon and southward Asian subtropical westerly jet, which can lead to increased (decreased) summer precipitation over southern China (over northern China and South Asia). The IPO plays a dominant role in connecting the decadal variations in precipitation between arid central Asia and monsoonal Asia by modulating the precipitation of their respective major rainy seasons. Model results suggest that this decadal linkage stems entirely from the internal variability present in the CESM-LME control and all single-forcing simulations. Changes in external forcing factors do not alter this inherent linkage caused by IPO. Moreover, based on analyses of the aridity index and soil moisture content, this relationship of precipitation variation also causes a similar decadal linkage of moisture changes in central Asia and monsoonal Asia. The differences in the multi-centennial-scale moisture/precipitation variations in the Asian arid region and the monsoon region between the Medieval Climate Anomaly and Little Ice Age are also likely caused by IPO-like sea surface temperature anomalies.
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Hongna Xu et al.
Status: final response (author comments only)
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RC1: 'Comment on cp-2023-53', Anonymous Referee #1, 26 Aug 2023
Summary: The objective of the manuscript is to disentangle the precipitation variability in Asia over the past millennium by analyzing data from climate model simulations driven by different forcing combinations and data from the last Millennium reanalysis Project. This latter data set results from polio data off-line assimilation into simulations with Earth-system models.
The main conclusion of the study is that a citation at multi-annual time stairs in this region displays a typo structure with northern Asia experiencing trial conditions and central and monsoonal Asia experiencing what conditions and vice versa. This structure is detectable in almost all climate simulations in the forcing and in the proxy-driven analysis. The authors conclude that this structure results from internal climate variability and is not associated with external forcing. The conclusion of the analysis is that this type of structure is associated with the Interdecadal Pacific Oscillation and with the impact of their sea surface temperature anomalies. Nevertheless, the authors also detect that this precipitation pattern is affected by the transition between the medieval climate anomaly and the Little Ice Age.
Recommendation:
The manuscript is very well written, the structure is very clear, and the analyses are all meaningful. Therefore, I am recommending the publication, but I do have a few comments that the authors may want to consider.
Main point:
1) The conclusion that the precipitation dipole is not affected by external forcing is not as solid as the authors believe. it is true that this structure appears in all empirical function analyses of almost all simulations regardless of the external forcing. However, it is possible that the precipitation dipole, despite being produced by internal climate variability, might still be affected by the external forcing so that its time variations could be affected by phases of strong or weak volcanism or strong or weak solar output. To some extent, the study leaves this possibility open when the authors found that the time evolution of the precipitation dipole is affected by the Little Ice Age.
The model setup used by the alphas could also be used to ascertain the hypothesis that external forcing also affects the time of evolution of the precipitation dipole, and the ensemble of simulations that the authors have used there are several driven by all forces if the forcing affects the possibilation dipole it can component of the empirical function, namely, the principal component should display some correlation across all simulations driven by all forcings. If the forcing has no impact, then this correlation across the simulations should be very small. Therefore, there is a relatively easy way to support the initial conclusion of the study.
Particular points:
2) ‘Additionally, considering
the superior performance of the Community Earth System Model (CESM) series in simulating Asian climate (Mishra and Aadhar, 2021; Ning et al., 2020; Xue et al., 2023),’
I would recommend rephrasing the sentence in a more specific way. In which sense is the CESM model superior? Does it produce better spatial patterns of precipitation or temperature or other recent trends, small realistic etc.. The judgements about the general superiority of a model about the models are usually unfair.
3) line 166 : measures the supply of soil water to the atmosphere. ‘
Evapo transpiration does not really measure the supply of soil water to the atmosphere but the atmospheric demand of water. This demand might be supplied if the soil is wet enough, but not necessarily
4) 164 ‘A larger aridity index indicates
that relatively more moisture remains in the land, whereas a smaller aridity index represents drier condition’
This definition of the aridity index is real because the reader may assume that a larger ability in the index would indicate trial conditions and vice versa.
5) Their ensemble pattern was also consistent with the reconstruction (Fig. 1b).’
how was the ensemble pattern calculated? is the sample pattern the average of all leading EOF patterns or was it calculated by concatenating all simulations in time ?
6) Conclusions discussion
In the present version of the manuscript, the discussion section comes after the conclusions, which is strange. Usually, the conclusion section is the last section in the manuscript. Also, the discussion section is rather limited. I address just the difference between the Little Ice Age and other periods regarding the precipitation dipole. This is a Small Part of the analysis, and the discussion's main points should be actually devoted to the issues of the precipitation dipole, internal availability, and external forcing.
Citation: https://doi.org/10.5194/cp-2023-53-RC1 -
AC1: 'Reply on RC1', Tao Wang, 14 Sep 2023
The comment was uploaded in the form of a supplement: https://cp.copernicus.org/preprints/cp-2023-53/cp-2023-53-AC1-supplement.pdf
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AC1: 'Reply on RC1', Tao Wang, 14 Sep 2023
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CC1: 'Comment on cp-2023-53', Liang Ning, 02 Oct 2023
Comments
Summary:
Based on reanalysis and simulations of the last millennium, the existence of the linkage between decadal changes in precipitation in arid central Asia and humid Asian monsoon regions was ascertained in this paper. The decadal linkage is characterized by the same changes in precipitation in arid central Asia and southern China, which were the opposite of those in the South Asian monsoon region and most of northern China. This paper also found that the internal variability associated with the Interdecadal Pacific Oscillation (IPO) plays a dominant role in connecting the decadal variations in precipitation between arid central Asia and monsoonal Asia by modulating the precipitation of their respective major rainy seasons. Besides, this decadal linkage of precipitation variation causes a similar decadal linkage between moisture changes in central Asia and monsoonal Asia.
Recommendation:
I think this paper is well written, well organized, and well diagramed. And this paper tried to ascertain and explain the observed decadal linkage between precipitation changes in Asian arid regions and monsoonal regions during the current period based on longer data (i.e., reanalysis and simulations of the last millennium), which is meaningful and interesting. However, I still have some comments. I think it is publishable after some comments in the following are considered.
Main comments:
(I) The “time period 850–2005” in captions of several figures (e.g., Fig. 7 and 9) is inaccurate, because the simulations forced by ozone and aerosols only cover the time period 1850–2005.
(II) Section 3.3 Processes of the IPO modulating the leading precipitation pattern is relatively long. It seems that this section is organized by the “Processes of the IPO modulating precipitation of major rainy seasons in central Asia” and “Processes of the IPO modulating precipitation of major rainy seasons in monsoonal Asia”. It would be easier to follow if the authors subdivide this section into two further subsections by adding subsection titles.
(III) It is interesting that the IPO plays a dominant role in connecting the decadal variations both in precipitation and in moisture between arid central Asia and monsoonal Asia. Besides, the variations in moisture conditions result from the combined effect of precipitation and PET, as indicated by the aridity index (AI). Then I wonder how IPO affects the PET and whether the impact of IPO on PET positively contributes to the decadal linkage of moisture changes in central Asia and monsoonal Asia or not.
Line by line comments:
Line 21 (‘output’ can be “outputs”)
Line 66 (‘EOF1’ can be “the first leading mode (EOF1)”)
Line 67 (‘LMR’ can be “Last Millennium Reanalysis (LMR)”)
Line 104 (‘this study will also utilize CESM…’ can be “this study also utilizes CESM…”)
Line 254 (‘Last Millennium Reanalysis dataset’ can be “LMR”)
Line 492 (‘abovementioned’ can be “aforementioned”)
Line 558 (‘above-mentioned’ can be “aforementioned”)
Citation: https://doi.org/10.5194/cp-2023-53-CC1 -
RC2: 'Comment on cp-2023-53', Anonymous Referee #2, 02 Oct 2023
Comments
Summary:
Based on reanalysis and simulations of the last millennium, the existence of the linkage between decadal changes in precipitation in arid central Asia and humid Asian monsoon regions was ascertained in this paper. The decadal linkage is characterized by the same changes in precipitation in arid central Asia and southern China, which were the opposite of those in the South Asian monsoon region and most of northern China. This paper also found that the internal variability associated with the Interdecadal Pacific Oscillation (IPO) plays a dominant role in connecting the decadal variations in precipitation between arid central Asia and monsoonal Asia by modulating the precipitation of their respective major rainy seasons. Besides, this decadal linkage of precipitation variation causes a similar decadal linkage between moisture changes in central Asia and monsoonal Asia.
Recommendation:
I think this paper is well written, well organized, and well diagramed. And this paper tried to ascertain and explain the observed decadal linkage between precipitation changes in Asian arid regions and monsoonal regions during the current period based on longer data (i.e., reanalysis and simulations of the last millennium), which is meaningful and interesting. However, I still have some comments. I think it is publishable after some comments in the following are considered.
Main comments:
(I) The “time period 850–2005” in captions of several figures (e.g., Fig. 7 and 9) is inaccurate, because the simulations forced by ozone and aerosols only cover the time period 1850–2005.
(II) Section 3.3 Processes of the IPO modulating the leading precipitation pattern is relatively long. It seems that this section is organized by the “Processes of the IPO modulating precipitation of major rainy seasons in central Asia” and “Processes of the IPO modulating precipitation of major rainy seasons in monsoonal Asia”. It would be easier to follow if the authors subdivide this section into two further subsections by adding subsection titles.
(III) It is interesting that the IPO plays a dominant role in connecting the decadal variations both in precipitation and in moisture between arid central Asia and monsoonal Asia. Besides, the variations in moisture conditions result from the combined effect of precipitation and PET, as indicated by the aridity index (AI). Then I wonder how IPO affects the PET and whether the impact of IPO on PET positively contributes to the decadal linkage of moisture changes in central Asia and monsoonal Asia or not.
Line by line comments:
Line 21 (‘output’ can be “outputs”)
Line 66 (‘EOF1’ can be “the first leading mode (EOF1)”)
Line 67 (‘LMR’ can be “Last Millennium Reanalysis (LMR)”)
Line 104 (‘this study will also utilize CESM…’ can be “this study also utilizes CESM…”)
Line 254 (‘Last Millennium Reanalysis dataset’ can be “LMR”)
Line 492 (‘abovementioned’ can be “aforementioned”)
Line 558 (‘above-mentioned’ can be “aforementioned”)
Citation: https://doi.org/10.5194/cp-2023-53-RC2
Hongna Xu et al.
Hongna Xu et al.
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