the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 28 Feb 2025
Factors Causing Stratocumulus to Deviate from Subtropical High Variability on Seasonal to Interannual Timescales
Abstract. Stratocumulus (Sc) covers the eastern flanks of maritime subtropical high pressure systems and exerts an influence on the global energy budget comparable to CO2. Previous studies have identified the temperature difference between 700 hPa and the surface as the primary driver of Sc variability. However, the mechanistic linkages between subtropical highs and this critical temperature gradient, which defines lower tropospheric stability, remain unresolved. While subsidence modulates temperatures at 700 hPa and wind-driven cooling affects surface temperatures, the observed decoupling between subtropical high intensity and Sc fraction on seasonal to interannual timescales lacks a mechanical explanation. This study uses reanalysis data to test two hypothesized pathways linking the strength of the subtropical highs to the lower tropospheric stability. Results demonstrate that neither pathway dominates, as correlations between Sc-regime temperatures and subtropical high dynamics exhibit strong regional and temporal dependencies, indicating that correlation does not apply causation. Additionally, Sc-regime conditions do not systematically align with subtropical high variability, highlighting the need for further investigation into the dynamical processes governing temperatures in the lower troposphere.
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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.
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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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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2025-876', Anonymous Referee #1, 24 Mar 2025
- AC1: 'Reply on RC1', Hairu Ding, 24 May 2025
-
RC2: 'Comment on egusphere-2025-876', Anonymous Referee #2, 31 Mar 2025
Review of "Factors causing stratocumulus to deviate
from subtropical high variability on seasonal to
interannual timescales"
by H. Ding, B. Stevens, and H. Schmidt[A] Overall recommendation
This study presents statistical analyses of observational
data for maritime stratocumulus cloud fraction andÂ
atmospheric conditions. The study discusses whether theÂ
cloud fraction is controlled by the atmosphericÂ
conditions, focusing on the strength of the subtropicalÂ
high pressure system.The issue addressed in the paper is important.Â
Stratocumulus cloud plays a major role in the globalÂ
energy budget, and therefore, its changes can lead toÂ
sizable impact on the global climate. This motivatesÂ
research on the factors controlling the stratocumulusÂ
cloud.This study forwards understanding of the issue byÂ
rejecting two hypothesized processes by which theÂ
subtropical highs may affect the stratocumulus cloud.
The authors also illustrate that correlation between
the stratocumulus regime temperatures and theÂ
subtropical high dynamics exhibit strong regional andÂ
temporal dependencies, which is a valuable piece ofÂ
information for those interested in the stratocumulusÂ
cloud variation.There are, however, some minor points to mentionÂ
regarding the presentation or interpretation of theÂ
results as listed below. I would therefore recommendÂ
accepting the manuscript for publication after minorÂ
revision.
[B] Minor Comments(1) P.3 L.65 "This paper uses the second version of
the ATSR-AATSR"Readers may be interested in the characteristics ofÂ
this data set when compared with other observationsÂ
such as ISCCP or MODIS. If the authors could commentÂ
on this, that will be helpful.(2) P.5 L.109 "... it is fixed to be 500m"
It would be helpful to readers if the authorsÂ
explain why the LCL is fixed to be 500m, ratherÂ
than being estimated.(3) P.5 Figure 2 caption "low cloud fraction (kappa)
from 2003 to 2014"This appears inconsistent with the statement inÂ
L.70, that low cloud fraction data for the period
from Jan 2003 to Dec 2011 is analyzed.(4) P.6 L.143 "C_D=0.0015 the drag coefficient"
Readers might wonder why the drag coefficient isÂ
assumed to be a constant value of 0.0015.
Additional clarification would be helpful.(5) P.7 Table 1 caption "The dominant contribution
to EIS is denoted by a bold font"It would be helpful to readers if the authors explain
in more detail what the dominant contribution means.
Does it mean that magnitude of the correlation or theÂ
standard deviation at one pressure level is largerÂ
than the magnitude at the other level?(6) P.7 L.158 "explain most of the variability in EIS"
Readers might wonder if this statement is supported by
Table 1, because magnitude of the correlation isÂ
smaller at 700hPa than at 1000hPa at NP and SI onÂ
interannual timescale.
Additional clarification would be helpful.(7) P.7 L.171 "this correlation does not imply causation"
Here the authors argue that the correlation does notÂ
imply causation. Does this argument apply to bothÂ
seasonal cycle and interannual variability, or does itÂ
apply to interannual variability only?
Additional clarification would be helpful.(8) P.8 Figure 3
I suggest that the authors give definition of the primesÂ
for EIS, Q_c, LHF_c, and W_E.(9) P.8 L.187 "a clear relationship between Q_c andÂ
omega_700,c"It would be helpful if the authors write the pressureÂ
level at which the Q_c is evaluated. Is it 700hPa?(10) P.10 L.204 "Upwelling areas are restricted to the
coastal regions where the wind-stress curl is large"In Figure 7(b), there appears to be no upwelling alongÂ
the equator in the Pacific and the Atlantic. ReadersÂ
might wonder how the SST cold tongue is maintained.
Additional clarification would be helpful.(11) P.10 L.207 "variations in near-surface geopotential
gradients are not the primary driver of changes in
theta_1000"It may be a good idea to show scatter plots forÂ
variations in geopotential gradients and variationsÂ
in theta_1000, for both seasonal and interannualÂ
timescales, so that readers can better follow theÂ
argument.
[C] Typos(1) P.6 L.133 "geopolitical"
geopotential?
(2) P.7 L.164 "SP"
SI?
(3) P.8 L.187 "theta_700"
omega_700?
(4) P.9 Figure 4 caption "omega_700(left)"
omega_700(top)?
(5) P.9 Figure 4 caption "Q(right)"
Q(bottom)?
(6) P.9 Figure 4 caption "Stratocumulus regions"
Subtropical high areas?
(7) P.12 Figure 8 caption "omega_700(top)"
omega_700(left)?
(8) P.12 Figure 8 caption "d(phi)/dx(bottom)"
d(phi)/dx(right)?
Â
Citation: https://doi.org/10.5194/egusphere-2025-876-RC2 - AC2: 'Reply on RC2', Hairu Ding, 24 May 2025
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2025-876', Anonymous Referee #1, 24 Mar 2025
- AC1: 'Reply on RC1', Hairu Ding, 24 May 2025
-
RC2: 'Comment on egusphere-2025-876', Anonymous Referee #2, 31 Mar 2025
Review of "Factors causing stratocumulus to deviate
from subtropical high variability on seasonal to
interannual timescales"
by H. Ding, B. Stevens, and H. Schmidt[A] Overall recommendation
This study presents statistical analyses of observational
data for maritime stratocumulus cloud fraction andÂ
atmospheric conditions. The study discusses whether theÂ
cloud fraction is controlled by the atmosphericÂ
conditions, focusing on the strength of the subtropicalÂ
high pressure system.The issue addressed in the paper is important.Â
Stratocumulus cloud plays a major role in the globalÂ
energy budget, and therefore, its changes can lead toÂ
sizable impact on the global climate. This motivatesÂ
research on the factors controlling the stratocumulusÂ
cloud.This study forwards understanding of the issue byÂ
rejecting two hypothesized processes by which theÂ
subtropical highs may affect the stratocumulus cloud.
The authors also illustrate that correlation between
the stratocumulus regime temperatures and theÂ
subtropical high dynamics exhibit strong regional andÂ
temporal dependencies, which is a valuable piece ofÂ
information for those interested in the stratocumulusÂ
cloud variation.There are, however, some minor points to mentionÂ
regarding the presentation or interpretation of theÂ
results as listed below. I would therefore recommendÂ
accepting the manuscript for publication after minorÂ
revision.
[B] Minor Comments(1) P.3 L.65 "This paper uses the second version of
the ATSR-AATSR"Readers may be interested in the characteristics ofÂ
this data set when compared with other observationsÂ
such as ISCCP or MODIS. If the authors could commentÂ
on this, that will be helpful.(2) P.5 L.109 "... it is fixed to be 500m"
It would be helpful to readers if the authorsÂ
explain why the LCL is fixed to be 500m, ratherÂ
than being estimated.(3) P.5 Figure 2 caption "low cloud fraction (kappa)
from 2003 to 2014"This appears inconsistent with the statement inÂ
L.70, that low cloud fraction data for the period
from Jan 2003 to Dec 2011 is analyzed.(4) P.6 L.143 "C_D=0.0015 the drag coefficient"
Readers might wonder why the drag coefficient isÂ
assumed to be a constant value of 0.0015.
Additional clarification would be helpful.(5) P.7 Table 1 caption "The dominant contribution
to EIS is denoted by a bold font"It would be helpful to readers if the authors explain
in more detail what the dominant contribution means.
Does it mean that magnitude of the correlation or theÂ
standard deviation at one pressure level is largerÂ
than the magnitude at the other level?(6) P.7 L.158 "explain most of the variability in EIS"
Readers might wonder if this statement is supported by
Table 1, because magnitude of the correlation isÂ
smaller at 700hPa than at 1000hPa at NP and SI onÂ
interannual timescale.
Additional clarification would be helpful.(7) P.7 L.171 "this correlation does not imply causation"
Here the authors argue that the correlation does notÂ
imply causation. Does this argument apply to bothÂ
seasonal cycle and interannual variability, or does itÂ
apply to interannual variability only?
Additional clarification would be helpful.(8) P.8 Figure 3
I suggest that the authors give definition of the primesÂ
for EIS, Q_c, LHF_c, and W_E.(9) P.8 L.187 "a clear relationship between Q_c andÂ
omega_700,c"It would be helpful if the authors write the pressureÂ
level at which the Q_c is evaluated. Is it 700hPa?(10) P.10 L.204 "Upwelling areas are restricted to the
coastal regions where the wind-stress curl is large"In Figure 7(b), there appears to be no upwelling alongÂ
the equator in the Pacific and the Atlantic. ReadersÂ
might wonder how the SST cold tongue is maintained.
Additional clarification would be helpful.(11) P.10 L.207 "variations in near-surface geopotential
gradients are not the primary driver of changes in
theta_1000"It may be a good idea to show scatter plots forÂ
variations in geopotential gradients and variationsÂ
in theta_1000, for both seasonal and interannualÂ
timescales, so that readers can better follow theÂ
argument.
[C] Typos(1) P.6 L.133 "geopolitical"
geopotential?
(2) P.7 L.164 "SP"
SI?
(3) P.8 L.187 "theta_700"
omega_700?
(4) P.9 Figure 4 caption "omega_700(left)"
omega_700(top)?
(5) P.9 Figure 4 caption "Q(right)"
Q(bottom)?
(6) P.9 Figure 4 caption "Stratocumulus regions"
Subtropical high areas?
(7) P.12 Figure 8 caption "omega_700(top)"
omega_700(left)?
(8) P.12 Figure 8 caption "d(phi)/dx(bottom)"
d(phi)/dx(right)?
Â
Citation: https://doi.org/10.5194/egusphere-2025-876-RC2 - AC2: 'Reply on RC2', Hairu Ding, 24 May 2025
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- 1
Hairu Ding
Bjorn Stevens
Hauke Schmidt
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(32134 KB) - Metadata XML