the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 20 May 2026
Marine Stratocumulus to Land Fog Transition in the Coastal Mountain-Range of Atacama Desert
Abstract. The advection of marine stratocumulus clouds (Sc) from the Southeast Pacific into the Atacama Desert forms extensive, semi-permanent fog banks at the top of the coastal mountain range. These fog banks provide the sole water input for xeric ecosystems and serve as a freshwater resource for human activities. To improve our understanding of this relevant system, we conducted a field experiment in July 2024 at the coastal Atacama called StraToFog to measure vertical profiles and near-surface parameters related to the marine boundary layer (MBL) state during the marine Sc-to-land fog transition. In this study, we aim to describe the campaign and present some of the first results from observations of the main processes at non-local and local scales during the Sc-fog transition. The vertical profile measurements reveal that the cloud-topped MBL frequently reaches ~15 km inland, with negligible thermal changes but a significant decrease in humidity, suggesting fog and water vapour retention on the coastal mountains. We found that maximum fog collection occurs in the afternoon, driven by a sea-to-land breeze that transports higher marine humidity, thereby increasing liquid water content. During the night, fog collection decreases due to lower wind speed and liquid water content resulting from lower air temperature. At the surface, our observations suggest that negative latent heat flux is produced by dewfall at dawn, water vapour adsorption during midday, and fog deposition over the afternoon. The StraToFog field experiment revealed key acting processes, linking spatial scales to understand atmospheric water pathways in this hyperarid environment.
- Preprint
(14247 KB) - Metadata XML
- BibTeX
- EndNote
Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-2396', Anonymous Referee #1, 24 Aug 2026
- RC2: 'Comment on egusphere-2026-2396', Anonymous Referee #2, 04 Sep 2026
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 312 | 193 | 35 | 540 | 30 | 22 |
- HTML: 312
- PDF: 193
- XML: 35
- Total: 540
- BibTeX: 30
- EndNote: 22
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
This study synthesizes observations from the StraToFog field campaign in coastal Atacama to analyze the evolution and surface impact of marine fog that forms in that region. Overall, the campaign methodology is sound and comprehensive. Their multi-site and instrument method of observing the thermodynamic state is foundational to be able to comment on the evolution of these clouds. Their findings that coastal fog is ultimately driven by moisture advection from the diurnal land-sea winds, and the synoptic pressure state, is substantiated by their measurements and consistent with general boundary layer theory. Consequently, their arguments for the advection of the marine boundary layer over the terrain and into the surface desert air mass above is sound. Their key discussion on the fate of the moisture from this airmass interacting with surface fluxes seems plausible. The authors could address specific mechanisms as further evidence for the surface interaction.
Specific Comments:
Line 135: The methodology of approximating the height of the boundary layer is sound, the calculations of the rate may be too definitive from their measurements. Is this a constant linear rate from the observations? If so, include that and perhaps some error bars.
Line 160: If you’re going to use the LCL from a sounding, the assumption is that the parcels that are generating the cloud are starting from the very surface. I think this is a good assumption given it’s reasonable to assume these marine clouds are formed from moisture fluxing off the surface, then rising. However, this is still an approximation, given that different layers of the atmosphere may be more moist (although, their measurements indicate the surface is the most moist). It would be good to quantify more of the uncertainty with this technique. Also, it’s interesting that they approximate the cloud top with a different technique than the LCL. Why was this the case?
Line 190: The claim that your measurements at the first few meters of the surface are significantly different between site C and site E and therefore an indication of fog deposition and evaporation to me are weak. First, I’m not sure if you’re using the same instrument in site C and E, it appears that one may be using a radiosonde, and the other a UAV. This would absolutely impact the results. If one of them is using a UAV, perhaps the drone sitting for a few minutes before launch could impact the first measurement being made. Furthermore, you have flux measurements of the 5 km, do these flux measurements match your claim? I see your point that you are arguing that it is a process that is happening at the very surface, but it’s a big jump to your claim of fog deposition and evaporation from one measurement at the surface on one event. Did this happen at other times throughout the campaign?
The system that is the fog deposition into the ground, is there some information in the literature of this process? I understand this may be out of the scope of the paper, but given it’s a key part of the findings, a few lines arguing it’s happening may be helpful. Additionally, is there a saturation and the speed at which this happens? Some comment on this process happening quickly at say the start of fog deposition (the ground is most dry) can help. Overall, some paragraph perhaps on the biology or soil moisture dynamics would help the author’s surface interactions claims.
Technical Corrections:
Given this was an important part of your analysis, I would add to your q mixing ratio a subscript of qv (for vapor) and qt (total mixing ratio), similar as you did to ql, to help the reader keep track of what mixing ratio you’re referring to.
In the figure captions, it would be beneficial if you included the instruments used to make these measurements, given the complexity of the field campaign, and you use different instruments to make claims about processes happening at the same layers.