Adjustments to an abrupt solar forcing in the CMIP6 abrupt-solm4p experiment

Lange, Charlotte; Quaas, Johannes

doi:https://doi.org/10.5194/egusphere-2024-3229

Preprints

https://doi.org/10.5194/egusphere-2024-3229

Preprints

04 Nov 2024

| 04 Nov 2024

Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Adjustments to an abrupt solar forcing in the CMIP6 abrupt-solm4p experiment

Charlotte Lange and Johannes Quaas

Abstract. The concept of "radiative" or "rapid" adjustments refers to the response of the climate system to an instantaneous radiative forcing, independent of surface temperature changes. These adjustments can occur over time scales from hours (e.g. aerosol-cloud-interactions) to months (e.g. stratospheric temperature changes) or even longer, making it challenging to distinguish adjustments from feedbacks over longer time scales. Despite variations in definitions, understanding these processes is essential for advancing climate modeling.

Strong volcanic eruptions, which produce scattering aerosol layers in the stratosphere, offer natural experiments to study short-term adjustments. However, the gradual spread of aerosols over the globe over months complicates analysis, requiring more controlled experiments. The abrupt-solm4p experiment within the Cloud Feedback Model Intercomparison Project (CFMIP) as part of the 6th Coupled Model Intercomparison Project (CMIP6) simulates an instantaneous 4 % reduction in the solar constant, starting from a pre-industrial run on 1 January 1850. This study analyzed changes in climate variables, cloud properties, and radiative fluxes over different time scales (hours, days, months and up to 150 years) to understand adjustment processes.

Four models were evaluated, showing initial rapid cooling, particularly over Antarctica and the southern hemisphere, slowing down the polar night jet, disrupting the polar vortex and increasing Arctic cloud cover. During the first month, the troposphere cools down faster than the ocean surface, decreasing vertical stability and increasing cloud cover over ocean, while the opposite effect happens in the tropics over land. This in turn affects land-sea-circulation. On longer time scales we find robust changes of cloudiness.

Received: 16 Oct 2024 – Discussion started: 04 Nov 2024

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.

Download & links

Charlotte Lange and Johannes Quaas

Status: open (until 16 Dec 2024)

Post a comment Subscribe to comment alert

RC1: 'Comment on egusphere-2024-3229', Anonymous Referee #1, 25 Nov 2024 reply

Review of “Adjustments to an abrupt solar forcing in the CMIP6 abrupt-solm4p experiment”
by Charlotte Lang and Johannes Quaas

This paper examines simulations of the abrupt-solm4p model experiment from four Earth system models that contributed to CMIP6. Specifically, the authors investigate the models’ respond over different timescales to an abrupt reduction of the solar constant. Through the majority of the paper they focus on the climate response on sub-daily, daily, monthly, and centennial timescales. Toward the end of the paper the authors use a linear regression with global mean surface temperature to calculate the effective radiative forcing, and instantaneous radiative adjustment in the top-of-atmosphere radiative fluxes and the cloud radiative effect output of the abrupt-solm4p model simulations. Although many of the results presented in this paper are novel and interesting, there are some deficiencies in this paper that make it not currently suitable for publication. Below I have listed my major comments that need to be addressed before this paper should be published.
1. The structure of the manuscript is flawed, where the introduction bears little relevance to most of the results shown. The title and introduction are about rapid adjustments and effective radiative forcing, while until Section 3.6 and figure 14 there are no results shown on the rapid adjustments or effective radiative forcing. Instead, nearly the entire paper focuses on the models’ response at different timescales and does nothing to distinguish the rapid adjustments from temperature mediated changes. Due to this discrepancy between the introduction and nearly the entire results section, there is not a cohesive story to the paper. This makes it difficult to understand why the results shown are significant and how they relate to the rest of the paper. I recommend the authors re-organize and rewrite a lot of the material to either be about the different timescales of response to solm4p, or about the rapid adjustments and ERF.
2. This paper is missing substantial literature review. This would include summarizing some of the most relevant studies in the introduction and explaining in the conclusions how the present results relate to the previous literature. I believe that this manuscript would benefit from discussion of how the changes in abrupt-solm4p relate to changes from CO2 forcing, and other studies that have looked at solar forcing. I would like to point the authors to a pair of recently published studies on models’ response to solar forcing that they might find relevant.
Aerenson, T., & Marchand, R. (2024). Cloud Responses to Abrupt Solar and CO2 Forcing: 1. Temperature Mediated Cloud Feedbacks. Journal of Geophysical Research: Atmospheres, 129(12), e2023JD040296. https://doi.org/10.1029/2023JD040296

Aerenson, T., Marchand, R., & Zhou, C. (2024). Cloud Responses to Abrupt Solar and CO2 Forcing: 2. Adjustment to Forcing in Coupled Models. Journal of Geophysical Research: Atmospheres, 129(12), e2023JD040297. https://doi.org/10.1029/2023JD040297

3. The manuscript is also lacking explanation of how the authors distinguish the forced response from internal variability. On timescales as short as hourly, daily, and yearly one would imagine that the modeled climate response would be susceptible to internal variability. As far as I can tell the manuscript does not include any description of how the authors remove the variability signal to isolate the forced response. Without doing so, one cannot determine if the response is due to changing phases of for example, ENSO or the NAO instead of a response to the change in the solar forcing. If the authors are doing something to distinguish the forced response from internal variability, it needs to be mentioned in the manuscript. Or alternatively, if the authors can show that the internal variability is much smaller than the forced response that would also be adequate but would also have to be shown in the manuscript.
4. The manuscript mentions “not shown” results a handful of times, nearly all of which had me wondering why it is not shown. Generally, if a result is important enough to discuss it is important enough to show. I understand that this paper is already quite long, so some of this could be provided in a supplement.

Reply

Citation: https://doi.org/10.5194/egusphere-2024-3229-RC1

Charlotte Lange and Johannes Quaas

Viewed

Total article views: 429 (including HTML, PDF, and XML)

HTML	PDF	XML	Total	BibTeX	EndNote
341	67	21	429	4	3

HTML: 341
PDF: 67
XML: 21
Total: 429
BibTeX: 4
EndNote: 3

Views and downloads (calculated since 04 Nov 2024)

Month	HTML	PDF	XML	Total
Nov 2024	321	62	21	404
Dec 2024	20	5	0	25

Cumulative views and downloads (calculated since 04 Nov 2024)

Month	HTML	PDF	XML	Total
Nov 2024	321	62	21	404
Dec 2024	20	5	0	25

Viewed (geographical distribution)

Total article views: 425 (including HTML, PDF, and XML) Thereof 425 with geography defined and 0 with unknown origin.

Country	#	Views	%

Latest update: 13 Dec 2024

Short summary

We studied how the Earth’s climate system adjusts to sudden changes in the energy budget, by analyzing data of four climate models, which simulated a 4 % reduction of incoming solar energy. We found rapid cooling of the atmosphere and shifts in cloud cover and atmospheric circulation patterns like land-sea-circulation. Our research helps to better understand cloud adjustments, which are a main source of uncertainty in climate models. This can improve future climate predictions.


Total:	0
HTML:	0
PDF:	0
XML:	0