| 09 Sep 2026
The influence of the Madden-Julian Oscillation and extratropical Rossby wave dynamics on daily to multi-day precipitation variability in the arid Middle East during the wet season
Abstract. Most of the annual precipitation in the arid Middle East falls on only a few days per year during the cool season, having important implications for water resources and hydrometeorological hazards. Previous studies have shown that daily precipitation in the Middle East is modulated by both intraseasonal variability in tropical convection related to the Madden-Julian Oscillation (MJO) and midlatitude Rossby wave dynamics. However, their respective contributions to precipitation variability and their underlying mechanisms remain largely unexplored. This study quantifies the separate and joint influence of the MJO and midlatitude Rossby wave dynamics on daily to multi-day precipitation variability in the arid Middle East during the wet season (November–April) and explores the underlying mechanisms. To this end, we use daily precipitation observations and atmospheric reanalysis data for the period 1979–2020 along with diagnostics of Rossby wave packets and Rossby wave breaking. Our findings indicate that the remote influence of the MJO and local midlatitude Rossby wave forcing operate largely independent of each other and exert an approximately equal influence on Middle Eastern precipitation variability. Consistent with previous studies, reduced (enhanced) tropical convection over the eastern Indian Ocean and Maritime Continent during MJO phases 8 and 1 (4 and 5) increases (decreases) precipitation by more than 50 %. MJO convective activity influences Middle Eastern precipitation through a baroclinic response in the regional tropical circulation, consistent with the Matsuno-Gill model, inducing anomalies in the upper- and lower-tropospheric circulation, in atmospheric moisture transport into the region, and in large-scale vertical motion over the region. The immediate influence of the MJO via the regional tropical circulation does not alter the propagation and breaking of Rossby waves into the region in a manner that is consistent with wet or dry conditions. However, our findings suggest an extratropical pathway through which the MJO modulates precipitation over the Middle East with an approximately two-week lag, extending wet or dry conditions induced by the immediate MJO influence. The concurrence of the MJO with anomalous Rossby wave forcing can amplify or mute the precipitation response that would be expected from midlatitude forcing alone through strengthening or weakening the atmospheric moisture supply and through reinforcing or offsetting large-scale vertical motion over the region. This study contributes to improved process understanding of tropical and extratropical controls on precipitation variability in the water-scarce Middle East with implications for medium-range to sub-seasonal prediction of precipitation and early warnings for drought and flood hazards.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Weather and Climate Dynamics.
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Review of “The influence of the Madden-Julian Oscillation and extratropical Rossby wave dynamics on daily to multi-day precipitation variability in the arid Middle East during the wet season” by de Vries et al.
Recommendation: Minor revisions
Summary: This manuscript examines the contributions of the Madden-Julian oscillation (MJO) and midlatitude Rossby waves to precipitation in the Middle East during November-April. Reduced MJO precipitation in the eastern Indian Ocean during certain phases is associated with an increase in precipitation in the Middle East through the induced circulation response and moisture transport. It is shown that the MJO and extratropical influence can add constructively to augment the precipitation response that would be due to extratropical forcing alone. The study has important implications for subseasonal prediction related to water resources in this region.
I find this study to be a valuable contribution to understanding the large scale conditions that contribute to heavy precipitation in the Middle East, and recommend that this study be published after some minor revisions. However, I do have some areas for improvement. Arguments and diagnostics need to be strengthened for the tropical and extratropical pathways by which the MJO affects the Middle East. The writing can also be clarified in places. A list of detailed comments are provided below.
Comments:
Line 23. Please try to reduce the use of parentheses in this way in the paper.
Lines 27-31. The discussion here is confusing. It is first stated that the MJO does not affect Rossby wave propagation, but then it states that the MJO modulates the Middle East at a lag through the extratropics. This seems to occur via a stationary Rossby wave response as argued in Figures 10 and 11. The distinction that is noted here becomes somewhat more clear to me after reading further in the paper, but it lacked clarity at this moment in the abstract. The confusion in my mind lies from convoluting the stationary Rossby waves forced by the MJO with the extratropical Rossby wave packets being discussed here and in Figure 2 and 3.
Line 167. What percentage of the grid cell needs to be land before it is defined as land versus ocean?
Figure 1a. The target area defined in this figure has a large zonal extent and spans about 50 degrees of longitude. Can it be justified that the MJO or midlatitude events produce precipitation anomalies of the same sign across the entire region? I would anticipate that precipitation anomalies of different sign often occur within this large region.
Line 236. The presence of purple hatching is difficult to see. Maybe consider ways to make it more apparent.
Line 250. “westerly” -> “westward”. Also, this pattern of moisture transport resembles a Matsuno-Gill response to suppressed MJO heating as moisture transport will be dominated by the lower tropospheric flow. This could be mentioned.
Line 329-330. I wonder how this relationship might be mediated by the Indian Ocean Diploe (IOD), given relationships between ENSO and the IOD, as well as the ability of the IOD to create a dipole-like precipitation structure that creates a convective dipole-like pattern across the Indian Ocean basin.
Line 349. I don’t see southwesterly transport anomalies (from the southwest) in this figure. Similarly, the northwesterly anomalies are maybe more perceptible in opposite phases, but still hard to see. The size of vectors in Figure 2 dwarfs these anomalies during the MJO composites, downplaying the importance of the MJO-driven anomalies in Figure 7. More discussion would be helpful.
Page 14, and Figures 10 and 11. Evidence of a wave train that extends from the west Pacific to the Middle East is not entirely convincing in these plots, and the geopotential anomaly pattern looks noisy. Possibly an analysis of wave activity flux vectors would help. Some mediation of this teleconnection signal by the NAO might also occur, as suggested by Figure 11c, and so relating the results here to prior work on the subject (e.g. Lin, Brunet, and Derome et al. 2009) could be helpful.
Figure 14. It is interesting that the magnitude of the height anomalies does not seem to scale with the transport anomalies and water vapor anomalies. Maybe this is because the transport and water vapor are dominated by the lower troposphere, whereas the 500 hPa height anomalies are shown?
Line 569. See the comment about my confusion in the abstract, as this might also be relevant here. Compare also with line 577.
Lines 606-608. I also feel that modeling is an important step to help verify the lagged MJO response through midlatitude stationary wave propagation.