- Titel
- Impact of volcanic aerosols on clouds in cloud-system-resolving simulations and satellite observations
- Zitierfähige Url:
- https://nbn-resolving.org/urn:nbn:de:bsz:15-qucosa2-925850
- Datum der Einreichung
- 10.07.2023
- Datum der Verteidigung
- 29.01.2024
- Abstract (EN)
- Increased anthropogenic aerosols result in an enhancement in cloud droplet number concentration (Nd), which consequently modifies cloud and precipitation processes. It is unclear how exactly cloud liquid water path (LWP) and cloud fraction respond to aerosol perturbations. A volcanic eruption may help to better understand and quantify the cloud response to external perturbations, with a focus on short-term cloud adjustments. The goal of the present study is to understand and quantify the response of clouds to a se- lected volcanic eruption and to thereby advance the fundamental understanding of the cloud response to external forcing. In this study we used the ICON (ICOsahedral Non-hydrostatic) model in its numerical weather prediction setup at a cloud-system-resolving resolution of 2.5 km horizontally, to simulate the region around the Holuhraun volcano for one week (1 – 7 September 2014). The ICON-NWP version employed in this study does not include an interactive aerosol model. Therefore a new method for cloud condensation nuclei (CCN) activation in a mi- crophysics scheme that was developed specifically for this study is introduced. The CCN values were determined by interpolating from look-up tables and considering the corresponding pressure (p) and vertical velocity (w) values within each grid-box of the atmospheric model. Moreover, in order to improve the comparison between cloud microphysical variables and satellite retrievals, the MODIS simulator from the COSP (CFMIP Observation Simulator Package) framework was implemented into the source code of ICON-NWP. A pair of simulations, with and without the volcanic aerosol plume, allowed us to as- sess the simulated effective radiative forcing and its mechanisms, as well as its impact on adjustments of LWP and cloud fraction to the perturbations of Nd. In comparison to MODIS (Moderate Resolution Imaging Spectroradiometer) satellite retrievals, a clear enhancement of Nd due to the volcanic aerosol is detected and attributed. In contrast, no changes in either LWP or cloud fraction could be attributed. The on average almost unchanged LWP is a result of some LWP enhancement for thick and a decrease for thin clouds. In addition for this case of eruption, further experiments to examine how aerosols from the Holuhraun volcanic eruption affected LWP in regional simulations were conducted. The experiments aimed at: I) Determining the influence of different horizontal resolutions in ICON-NWP on LWP sensitivity. II) Assessing the sensitivity of LWP to changes in the autoconversion rate within the models. III) Comparing the responses of LWP and total column cloud droplet number concentration to the Holuhraun volcano eruption using different atmospheric models. The analysis indicates that increasing the horizontal resolution leads to higher LWP values in the model. However, the difference is not particularly significant, and the overall signal remains consistent in the volcano and no-volcano simulations across the three different resolutions. When the auto-conversion rate is increased by 10 times, there is a general reduction in LWP compared to the default rate. In addition, even relatively shallow clouds are sensitive to aerosol perturbations. Therefore, a larger number of clouds are affected by the volcanic plume in this scenario compared to the default auto-conversion case. When the auto-conversion rate is decreased by a factor of 10, there is a rise in LWP compared to the default rate. Our finding suggests that thicker clouds are more sensitive to aerosol perturbations in this case Comparative analysis of simulation results using different atmospheric models (ICON NWP, ICON-ART, and MetOffice Unified Model) for the Holuhraun volcano demonstrated consistent enhancements in total column Nd and LWP within the plume region compared to the no-volcano simulations. However, the magnitudes of the enhancements varied significantly between the different models. In order to examine the impact of these aerosols on a cloud regime different from the Holuhraun case, the Kilauea eruption and La Soufrière eruption, which occurred in low latitudes were examined with the same methodology. Our analyses revealed that in both cases, a comparison of both simulations with MODIS retrievals shows that the simulated Nd is considerably higher than the satellite data. It is plausible that the MODIS data may be influenced by the broken clouds, leading to an overestimation of the effective radius and consequently a lower Nd. In the Kilauea case, in LWP a relative enhancement by 14% inside the plume compared to outside the plume was obtained. However, in the La Soufrière eruption, the LWP inside the plume in the volcano and no-volcano simulations indicate that LWP does not differ significantly. In conclusion, the impact of volcanic eruption-induced aerosols on the LWP response is heavily influenced by cloud regimes. Also other model assumptions like the relevance of the precipitation formation rate as a cloud water sink play a role. However, in none of the simulations, a significant overall change in LWP that would have been plausibly consistent with observations was found.
- Freie Schlagwörter (EN)
- Aerosol-Cloud-Interaction Volcanos-Eruption Climate
- Klassifikation (DDC)
- 530
- Den akademischen Grad verleihende / prüfende Institution
- Universität Leipzig, Leipzig
- Version / Begutachtungsstatus
- publizierte Version / Verlagsversion
- URN Qucosa
- urn:nbn:de:bsz:15-qucosa2-925850
- Veröffentlichungsdatum Qucosa
- 12.07.2024
- Dokumenttyp
- Dissertation
- Sprache des Dokumentes
- Englisch
- Lizenz / Rechtehinweis
CC BY 4.0