the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 Apr 2025
Interdecadal shift in the impact of winter land-sea thermal contrasts on following spring transcontinental dust transport pathways in North Africa
Abstract. North Africa, the largest and most active dust source region globally, plays a critical role in the Earth's environment by dispersing dust over remote areas, especially in terms of circum-global transport that occurred many times since the 21st century. As a key indicator of the thermodynamic structure and dynamical circulation of the troposphere, the land-sea thermal contrast (LSC) could influence the variability of dust and subsequent large-scale propagation, but the extent of such influence is still unknown. This study reveals that around the late 1990s, the influence of pre-winter LSC on the spring dust transport pathway is reversed in North Africa, which is attributed to the bridging effect of the North Atlantic Oscillation (NAO). Before 2000, the warm land-cold ocean pattern in pre-winter is typically associated with the NAO+ mode, and the anomalous northeasterly and zonal circulation in the following spring facilitate the westward transport of dust from the lower troposphere in West North Africa towards the Atlantic. After 2000, the reversed zonal temperature pattern leads to the NAO− mode and enhances mid-latitude westerlies in winter, which persists into the next spring. Under conditions of unusually dry soil and strong dry convection, dust is mixed into the mid-to-upper troposphere and subsequently transported eastward globally, affecting regions including West Asia, northern China, the Pacific, and southeastern North America after 2000. This study underscores the critical role of sea-land-atmosphere interaction in circum-global dust propagation and offers new perspectives for investigating dust changes mechanism in the context of climate change.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(3660 KB) - Metadata XML
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Supplement
(1172 KB) - BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2025-826', Anonymous Referee #1, 29 Apr 2025
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AC1: 'Reply on RC1', Qi Wen, 04 May 2025
We sincerely appreciate your time and constructive feedback on our manuscript. Your comments and valuable suggestions have helped us improve the clarity and presentation of our work. Below, we address your specific concerns point by point, and we hope the responses adequately address your concerns.
- Choice of Periods
Comment: Section 2.1.3. Lines 147-151. The choice of these periods is not very clear, and it should be justified. In addition, are the conclusions depending on this choice?
Response:
Thanks for your suggestion! We agree that the rationale for selecting the two periods (1980–2000 and 2001–2023) should be clarified. These periods are chosen based on:
- We tested the PC of the dust field from SVD decomposition by a sliding t-test and found a significant climatic abruptness in 2000 (p<0.05), a conclusion that is also consistent with previous dust studies (e.g., Liu et al., 2023).
- Global warming (global warming acceleration and stagnation phases) and atmospheric circulation changed significantly in the late 1990s (e.g., Fyfe et al., 2013; Salinger et al., 2005).
- The two periods are also selected to take into account the fact that the composite sample sizes of the two periods are comparable and do not overlap.
This multi-faceted approach to period selection ensures our analysis captures genuine climate-dust relationships rather than artificial temporal artifacts. We have verified that our main conclusions remain unchanged when using different window lengths. Specifically, Fig. 2e (L226) in the original manuscript shows that the dust field PC exhibits a stable and significant sliding correlation with the land-sea thermal contrast index beginning in the early 21st century (multiple window lengths (15, 17, 21, and 23 years)), suggesting that the conclusions are robust. We will include the above justifications in the revised manuscript.
- Figure Readability
Comment: In my opinion, most of the figures are quite small and not easily readable when printed. The dashed dot vectors are not visible at all.
Response:
Thanks for your suggestion! We apologize for the suboptimal figure quality. In the revised version, we will:
(1) Enlarge all figures and adjust line weights/colors for better visibility.
(2) Zoom in and replace the high contrast pattern ensures that the dashed dot vectors are clearly visible.
(3) Provide high-resolution versions (e.g., 800 dpi) for printing.
- Bold Text in Figure Captions
Comment: I would eliminate the bold part of each Figure caption.
Response:
Thanks for your suggestion! We will revise all figure captions to use standard formatting (no bold text) for consistency with journal style.
- Statistical Threshold
Comment: Line 294. Why using a threshold of 0.1 for p rather than the usual one of 0.05. Could the conclusions change if a more standard threshold if chosen?
Response:
We sincerely appreciate this thoughtful question, as it rightly highlights an important methodological consideration in statistical analysis. We re-ran all analyses with p < 0.05 and found that the primary conclusions (e.g., shifts in dust pathways and anomalous cyclonic and anticyclonic circulation) remain valid, though some regional details become less pronounced. However, our choice of p < 0.1 is carefully considered and aligns with several previous studies examining decadal-scale climate variability (e.g., Liu et al., 2023). This slightly more lenient threshold is sometimes warranted, due to the limited sample size of decadal periods and to maintain the continuity of the dust transport path.
Reference:
Fyfe J C, Gillett N P, Zwiers F W. Overestimated global warming over the past 20 years[J]. Nature Climate Change, 2013, 3(9): 767-769.
Liu G, Li J, Ying T. The shift of decadal trend in Middle East dust activities attributed to North Tropical Atlantic variability[J]. Science Bulletin, 2023, 68(13): 1439-1446.
Salinger M J. Climate variability and change: past, present and future–an overview[J]. Climatic change, 2005, 70(1): 9-29.
Citation: https://doi.org/10.5194/egusphere-2025-826-AC1
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AC1: 'Reply on RC1', Qi Wen, 04 May 2025
-
RC2: 'Comment on egusphere-2025-826', Anonymous Referee #3, 02 Jul 2025
This study presents a timely and compelling investigation into the interdecadal shift (~late 1990s) in the relationship between winter land-sea thermal contrast (LSC) and spring dust transport pathways from North Africa. The authors identify the North Atlantic Oscillation (NAO) as a key bridge mechanism and demonstrate a transition from westward (pre-2000) to eastward/circum-global (post-2000) dust transport. The findings have implications for dust prediction, climate modeling, and assessing downstream environmental impacts. My specific comments are as follows:
- Regarding the choice of 1980–2000 and 2001–2023 periods is based on a sliding t-test, please give period splitting justification. For example, include the sliding t-test figure in supplementary materials to validate the 1990s shift. Alternatively, apply objective change-point detection (e.g., Pettitt test) to strengthen the rationale for the bifurcation.
- The results mention an increase in dust emissions after 2000 due to the drying of soils as a result of anomalous warming (Fig. 5g). However, quantitative analyses (e.g., regression of dust emissions on soil moisture) are not provided in the figure.
- CMIP6 results (Fig. S2) broadly support observations but lack discussion of model spread/uncertainty. I recommend quantify inter-model agreement (e.g., % of models showing significant correlations) and discuss limitations.
- It is important to emphasize the practical implications of the shift in conclusion.
- It is recommended that the text appearing in all figures be formatted consistently (Fig 6) and that the font be made larger.
Citation: https://doi.org/10.5194/egusphere-2025-826-RC2
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2025-826', Anonymous Referee #1, 29 Apr 2025
General comment
The paper investigates the influence of land-sea thermal contrasts on the dust transport from north Africa and the interdecadal shift of pathways. The topic is interesting and the paper well written and suitable for the Journal. I only have suggestions for a few minor points.
Specific comments
Section 2.1.3. Lines 147-151. The choice of these periods is not very clear, and it should be justified. In addition, are the conclusions depending on this choice?
In my opinion, most of the figures are quite small and not easily readable when printed. The dashed dot vectors are not visible at all.
I would eliminate the bold part of each Figure caption.
Line 294. Why using a threshold of 0.1 for p rather than the usual one of 0.05. Could the conclusions change if a more standard threshold if chosen?
Citation: https://doi.org/10.5194/egusphere-2025-826-RC1 -
AC1: 'Reply on RC1', Qi Wen, 04 May 2025
We sincerely appreciate your time and constructive feedback on our manuscript. Your comments and valuable suggestions have helped us improve the clarity and presentation of our work. Below, we address your specific concerns point by point, and we hope the responses adequately address your concerns.
- Choice of Periods
Comment: Section 2.1.3. Lines 147-151. The choice of these periods is not very clear, and it should be justified. In addition, are the conclusions depending on this choice?
Response:
Thanks for your suggestion! We agree that the rationale for selecting the two periods (1980–2000 and 2001–2023) should be clarified. These periods are chosen based on:
- We tested the PC of the dust field from SVD decomposition by a sliding t-test and found a significant climatic abruptness in 2000 (p<0.05), a conclusion that is also consistent with previous dust studies (e.g., Liu et al., 2023).
- Global warming (global warming acceleration and stagnation phases) and atmospheric circulation changed significantly in the late 1990s (e.g., Fyfe et al., 2013; Salinger et al., 2005).
- The two periods are also selected to take into account the fact that the composite sample sizes of the two periods are comparable and do not overlap.
This multi-faceted approach to period selection ensures our analysis captures genuine climate-dust relationships rather than artificial temporal artifacts. We have verified that our main conclusions remain unchanged when using different window lengths. Specifically, Fig. 2e (L226) in the original manuscript shows that the dust field PC exhibits a stable and significant sliding correlation with the land-sea thermal contrast index beginning in the early 21st century (multiple window lengths (15, 17, 21, and 23 years)), suggesting that the conclusions are robust. We will include the above justifications in the revised manuscript.
- Figure Readability
Comment: In my opinion, most of the figures are quite small and not easily readable when printed. The dashed dot vectors are not visible at all.
Response:
Thanks for your suggestion! We apologize for the suboptimal figure quality. In the revised version, we will:
(1) Enlarge all figures and adjust line weights/colors for better visibility.
(2) Zoom in and replace the high contrast pattern ensures that the dashed dot vectors are clearly visible.
(3) Provide high-resolution versions (e.g., 800 dpi) for printing.
- Bold Text in Figure Captions
Comment: I would eliminate the bold part of each Figure caption.
Response:
Thanks for your suggestion! We will revise all figure captions to use standard formatting (no bold text) for consistency with journal style.
- Statistical Threshold
Comment: Line 294. Why using a threshold of 0.1 for p rather than the usual one of 0.05. Could the conclusions change if a more standard threshold if chosen?
Response:
We sincerely appreciate this thoughtful question, as it rightly highlights an important methodological consideration in statistical analysis. We re-ran all analyses with p < 0.05 and found that the primary conclusions (e.g., shifts in dust pathways and anomalous cyclonic and anticyclonic circulation) remain valid, though some regional details become less pronounced. However, our choice of p < 0.1 is carefully considered and aligns with several previous studies examining decadal-scale climate variability (e.g., Liu et al., 2023). This slightly more lenient threshold is sometimes warranted, due to the limited sample size of decadal periods and to maintain the continuity of the dust transport path.
Reference:
Fyfe J C, Gillett N P, Zwiers F W. Overestimated global warming over the past 20 years[J]. Nature Climate Change, 2013, 3(9): 767-769.
Liu G, Li J, Ying T. The shift of decadal trend in Middle East dust activities attributed to North Tropical Atlantic variability[J]. Science Bulletin, 2023, 68(13): 1439-1446.
Salinger M J. Climate variability and change: past, present and future–an overview[J]. Climatic change, 2005, 70(1): 9-29.
Citation: https://doi.org/10.5194/egusphere-2025-826-AC1
-
AC1: 'Reply on RC1', Qi Wen, 04 May 2025
-
RC2: 'Comment on egusphere-2025-826', Anonymous Referee #3, 02 Jul 2025
This study presents a timely and compelling investigation into the interdecadal shift (~late 1990s) in the relationship between winter land-sea thermal contrast (LSC) and spring dust transport pathways from North Africa. The authors identify the North Atlantic Oscillation (NAO) as a key bridge mechanism and demonstrate a transition from westward (pre-2000) to eastward/circum-global (post-2000) dust transport. The findings have implications for dust prediction, climate modeling, and assessing downstream environmental impacts. My specific comments are as follows:
- Regarding the choice of 1980–2000 and 2001–2023 periods is based on a sliding t-test, please give period splitting justification. For example, include the sliding t-test figure in supplementary materials to validate the 1990s shift. Alternatively, apply objective change-point detection (e.g., Pettitt test) to strengthen the rationale for the bifurcation.
- The results mention an increase in dust emissions after 2000 due to the drying of soils as a result of anomalous warming (Fig. 5g). However, quantitative analyses (e.g., regression of dust emissions on soil moisture) are not provided in the figure.
- CMIP6 results (Fig. S2) broadly support observations but lack discussion of model spread/uncertainty. I recommend quantify inter-model agreement (e.g., % of models showing significant correlations) and discuss limitations.
- It is important to emphasize the practical implications of the shift in conclusion.
- It is recommended that the text appearing in all figures be formatted consistently (Fig 6) and that the font be made larger.
Citation: https://doi.org/10.5194/egusphere-2025-826-RC2
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Qi Wen
Yan Li
Mengying Du
Wenjun Song
Linbo Wei
Zhilan Wang
Xu Li
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(3660 KB) - Metadata XML
-
Supplement
(1172 KB) - BibTeX
- EndNote
- Final revised paper
General comment
The paper investigates the influence of land-sea thermal contrasts on the dust transport from north Africa and the interdecadal shift of pathways. The topic is interesting and the paper well written and suitable for the Journal. I only have suggestions for a few minor points.
Specific comments
Section 2.1.3. Lines 147-151. The choice of these periods is not very clear, and it should be justified. In addition, are the conclusions depending on this choice?
In my opinion, most of the figures are quite small and not easily readable when printed. The dashed dot vectors are not visible at all.
I would eliminate the bold part of each Figure caption.
Line 294. Why using a threshold of 0.1 for p rather than the usual one of 0.05. Could the conclusions change if a more standard threshold if chosen?