the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 31 Jan 2025
Failed cyclogenesis of a mesoscale convective system near Cape Verde: The role of the Saharan trade wind layer among other inhibiting factors observed during the CADDIWA field campaign
Abstract. The role of the Saharan air layer in Cape Verde cyclogenesis remains uncertain. Here, we investigate the inhibiting factors leading to the failed cyclogenesis of the mesoscale convective system (MCS) Pierre Henri (PH) observed during two flights of the CADDIWA campaign. We use CADDIWA data and a convection-permitting simulation run with the Meso-NH model. We show that the African easterly wave in which PH is embedded forms a marsupial pouch that keeps the SAL away from PH. On the contrary, a dusty, dry and warm air layer between 0.8 and 2 km altitude, called Saharan trade wind layer (STWL), penetrates into PH convective core, increasing the convective inhibition (CIN) area, and contributing up to 40 % of the CIN area during the MCS mature phase. The cold pools produced by convection also increase the CIN area, and contribute up to 50 % of this area after the MCS intense phase. Upper tropospheric (UT) dry air, with relative humidity below 15 % between 7 and 11 km altitude, gradually penetrates into the 150 km circle around PH, reaching 18 % of the area during its dissipation phase, preventing the MCS anvil expansion. The inhibiting roles of the STWL, cold pools, and UT dry air in leading the cyclogenesis to fail provide new insights into the complex dynamics of cyclogenesis in the Cape Verde region and challenge the existing model of the SAL.
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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
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Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2025-105', Anonymous Referee #1, 12 Feb 2025
This study investigates the inhibiting factors that led to the failed cyclogenesis of the mesoscale convective system (MCS) Pierre Henri (PH), observed during the CADDIWA field campaign. Using high-resolution airborne observations and a convection-permitting Meso-NH model, the authors analyze the interactions between the Saharan Air Layer (SAL), the Saharan Trade Wind Layer (STWL), cold pools, and upper tropospheric (UT) dry air. The study finds that: 1) the STWL, a relatively underexplored feature, played a significant role in increasing convective inhibition (CIN), contributing up to 40% of CIN during the mature phase of PH; 2) cold pools generated by convection further suppressed cyclone development, with their CIN contribution peaking at 50% post-intense phase; and 3) UT dry air limited the MCS's anvil expansion, with relative humidity below 15% between 7 and 11 km altitude, covering 18% of the MCS environment during dissipation. The findings are well-supported by observational data and validated against numerical simulations. I only have two minor comments for the authors to consider.
The study focuses on the failed cyclogenesis of one MCS (PH), but it is unclear how representative these findings are for other storms in the Cape Verde region. It would be interesting to more comprehensively compare the findings in this study with past ones on failed and/or successful Cape Verde cyclogenesis cases to improve the broader implications.
While the study effectively shows that STWL increased CIN, the mechanism of STWL intrusion into the MCS and its modification of convective processes needs clearer explanation. I suggest further elaborating on how weak low-level circulation allows STWL intrusion based on the current analysis.
Citation: https://doi.org/10.5194/egusphere-2025-105-RC1 - AC2: 'Reply on RC1', Guillaume Feger, 15 Apr 2025
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RC2: 'Comment on egusphere-2025-105', Anonymous Referee #2, 10 Apr 2025
Review of"Failed cyclogenesis of a mesoscale convective system near Cape Verde: The role of the Saharan trade wind layer among other inhibiting factors observed during the CADDIWA field campaign"by G.Feger et al, submitted to ACP.This article presents a study on the cyclogenesis as observed and modelled after a Caddiwa field campaign case study. The goal is to explain why a Mesoscale Convective System (MCS) failed to produce a cyclogenesis often observed over the Atlantic sea under the wind of the Saharan air layer (SAL). Using aircraft measurements data and convection-permitting simulation run with the Meso-NH model, the authors show that some African easterly waves inhibit the impact of the SAL on the MCS. The article concludes that observations confirm the factors already known. The added value of the study is that it quantifies these factors in a specific case.The article is clear and well written, even if it is full of acronyms and numbers that make it hard to understand the sentence and what the authors are trying to show. It can be accepted for publication after answering a few questions.Major comments:The main comment is the status of a single 'studied case' of this work. It is interesting to analyse the observations and the model in detail in order to quantify the impact of the various processes involved in maintaining cyclogenesis or not. But is this a specific case or a more general conclusion? To what extent can this study and its conclusions be considered generalizable? And if not, what more systematic data than a measurement campaign would enable this categorisation to be made more systematically?Is the present analysis confirmed by other cases where the cyclogenesis not failed and for the reasons proposed in this study? (other already published articles about cyclogenesis in this region?)Finally, in a forecasting context, is it possible to set thresholds for the various factors and thus know in advance whether cyclogenesis will take place or not?Minor comments:l.12 Acronyms may be useful but too much acronyms make reading difficult. Only in the abstract: MCS, CADDIWA, Meso-NH, PH, SAL, STWL, CIN, UT.l.25: "... on going debate (Shu and Wu, 2009)". Very long debate. A more recent reference?l.4 A "protective shell" in place of 'marsupial pouch'?? is this a common way of describing this atmospheric phenomenon?l.61: the 'respective' role? because the fact they have a role seems to be already known.l.82 It is necessary to have a top domain at 26 km ASL for this kind of study? Would not it be more interesting, for the same calculation cost, to have a lower top and therefore a thinner first vertical cell depth than 30m? Is 24h enough for the spin-up (i.e absorb the impact of the large scale due to the initial conditions)?l.205 Again about initial conditions: why not use the same model as input knowing forecast was made for the previous days?Figure 5: what is the unit for the dust concentrations in cm-3? number of particles/cm3? mass per cm3? a concentration is 'something' per 'volume'.l.242 what is the meaning of an 'accumulation mode' for dust? Is it possible than other aerosols are present in the studied plume?l.244 What is the definition of fine and coarse aerosol?l.288 what is the reference for this treshold of 10 ?/cm-3 to define the STWL?Citation: https://doi.org/
10.5194/egusphere-2025-105-RC2 - AC1: 'Reply on RC2', Guillaume Feger, 15 Apr 2025
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2025-105', Anonymous Referee #1, 12 Feb 2025
This study investigates the inhibiting factors that led to the failed cyclogenesis of the mesoscale convective system (MCS) Pierre Henri (PH), observed during the CADDIWA field campaign. Using high-resolution airborne observations and a convection-permitting Meso-NH model, the authors analyze the interactions between the Saharan Air Layer (SAL), the Saharan Trade Wind Layer (STWL), cold pools, and upper tropospheric (UT) dry air. The study finds that: 1) the STWL, a relatively underexplored feature, played a significant role in increasing convective inhibition (CIN), contributing up to 40% of CIN during the mature phase of PH; 2) cold pools generated by convection further suppressed cyclone development, with their CIN contribution peaking at 50% post-intense phase; and 3) UT dry air limited the MCS's anvil expansion, with relative humidity below 15% between 7 and 11 km altitude, covering 18% of the MCS environment during dissipation. The findings are well-supported by observational data and validated against numerical simulations. I only have two minor comments for the authors to consider.
The study focuses on the failed cyclogenesis of one MCS (PH), but it is unclear how representative these findings are for other storms in the Cape Verde region. It would be interesting to more comprehensively compare the findings in this study with past ones on failed and/or successful Cape Verde cyclogenesis cases to improve the broader implications.
While the study effectively shows that STWL increased CIN, the mechanism of STWL intrusion into the MCS and its modification of convective processes needs clearer explanation. I suggest further elaborating on how weak low-level circulation allows STWL intrusion based on the current analysis.
Citation: https://doi.org/10.5194/egusphere-2025-105-RC1 - AC2: 'Reply on RC1', Guillaume Feger, 15 Apr 2025
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RC2: 'Comment on egusphere-2025-105', Anonymous Referee #2, 10 Apr 2025
Review of"Failed cyclogenesis of a mesoscale convective system near Cape Verde: The role of the Saharan trade wind layer among other inhibiting factors observed during the CADDIWA field campaign"by G.Feger et al, submitted to ACP.This article presents a study on the cyclogenesis as observed and modelled after a Caddiwa field campaign case study. The goal is to explain why a Mesoscale Convective System (MCS) failed to produce a cyclogenesis often observed over the Atlantic sea under the wind of the Saharan air layer (SAL). Using aircraft measurements data and convection-permitting simulation run with the Meso-NH model, the authors show that some African easterly waves inhibit the impact of the SAL on the MCS. The article concludes that observations confirm the factors already known. The added value of the study is that it quantifies these factors in a specific case.The article is clear and well written, even if it is full of acronyms and numbers that make it hard to understand the sentence and what the authors are trying to show. It can be accepted for publication after answering a few questions.Major comments:The main comment is the status of a single 'studied case' of this work. It is interesting to analyse the observations and the model in detail in order to quantify the impact of the various processes involved in maintaining cyclogenesis or not. But is this a specific case or a more general conclusion? To what extent can this study and its conclusions be considered generalizable? And if not, what more systematic data than a measurement campaign would enable this categorisation to be made more systematically?Is the present analysis confirmed by other cases where the cyclogenesis not failed and for the reasons proposed in this study? (other already published articles about cyclogenesis in this region?)Finally, in a forecasting context, is it possible to set thresholds for the various factors and thus know in advance whether cyclogenesis will take place or not?Minor comments:l.12 Acronyms may be useful but too much acronyms make reading difficult. Only in the abstract: MCS, CADDIWA, Meso-NH, PH, SAL, STWL, CIN, UT.l.25: "... on going debate (Shu and Wu, 2009)". Very long debate. A more recent reference?l.4 A "protective shell" in place of 'marsupial pouch'?? is this a common way of describing this atmospheric phenomenon?l.61: the 'respective' role? because the fact they have a role seems to be already known.l.82 It is necessary to have a top domain at 26 km ASL for this kind of study? Would not it be more interesting, for the same calculation cost, to have a lower top and therefore a thinner first vertical cell depth than 30m? Is 24h enough for the spin-up (i.e absorb the impact of the large scale due to the initial conditions)?l.205 Again about initial conditions: why not use the same model as input knowing forecast was made for the previous days?Figure 5: what is the unit for the dust concentrations in cm-3? number of particles/cm3? mass per cm3? a concentration is 'something' per 'volume'.l.242 what is the meaning of an 'accumulation mode' for dust? Is it possible than other aerosols are present in the studied plume?l.244 What is the definition of fine and coarse aerosol?l.288 what is the reference for this treshold of 10 ?/cm-3 to define the STWL?Citation: https://doi.org/
10.5194/egusphere-2025-105-RC2 - AC1: 'Reply on RC2', Guillaume Feger, 15 Apr 2025
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Guillaume Feger
Jean-Pierre Chaboureau
Thibaut Dauhut
Julien Delanoë
Pierre Coutris
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(9412 KB) - Metadata XML