Developing a Cloud Scheme With Prognostic Cloud Fraction and Two Moment Microphysics for ECHAM‐HAM

Münch, Steffen; Lohmann, Ulrike

doi:10.1029/2019ms001824

Cited by 25 publications

(32 citation statements)

References 136 publications

(307 reference statements)

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“…The detrained cloud condensate is used as a source term for the cloud condensate treated by the CLOUD submodel and is considered in the liquid or ice phase depending on its temperature (if temperature is lower than −35 • C, the phase is ice; otherwise it is liquid). In this work, the scheme of Tiedtke (1989) with modifications by Nordeng (1994) has been used. The CLOUD submodel describes physical and microphysical processes in large-scale stratiform clouds.…”

Section: Numerical Representation Of Cloudsmentioning

confidence: 99%

Cold cloud microphysical process rates in a global chemistry–climate model

et al. 2021

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Abstract. Microphysical processes in cold clouds which act as sources or sinks of hydrometeors below 0 ∘C control the ice crystal number concentrations (ICNCs) and in turn the cloud radiative effects. Estimating the relative importance of the cold cloud microphysical process rates is of fundamental importance to underpin the development of cloud parameterizations for weather, atmospheric chemistry, and climate models and to compare the output with observations at different temporal resolutions. This study quantifies and investigates the ICNC rates of cold cloud microphysical processes by means of the chemistry–climate model EMAC (ECHAM/MESSy Atmospheric Chemistry) and defines the hierarchy of sources and sinks of ice crystals. Both microphysical process rates, such as ice nucleation, aggregation, and secondary ice production, and unphysical correction terms are presented. Model ICNCs are also compared against a satellite climatology. We found that model ICNCs are in overall agreement with satellite observations in terms of spatial distribution, although the values are overestimated, especially around high mountains. The analysis of ice crystal rates is carried out both at global and at regional scales. We found that globally the freezing of cloud droplets and convective detrainment over tropical land masses are the dominant sources of ice crystals, while aggregation and accretion act as the largest sinks. In general, all processes are characterized by highly skewed distributions. Moreover, the influence of (a) different ice nucleation parameterizations and (b) a future global warming scenario on the rates has been analysed in two sensitivity studies. In the first, we found that the application of different parameterizations for ice nucleation changes the hierarchy of ice crystal sources only slightly. In the second, all microphysical processes follow an upward shift in altitude and an increase by up to 10 % in the upper troposphere towards the end of the 21st century.

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Section: Numerical Representation Of Cloudsmentioning

confidence: 99%

Cold cloud microphysical process rates in a global chemistry–climate model

et al. 2021

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“…As the magnitude of the saturation ratio in the updraft is related to the vertical velocity, a fictitious downdraft is introduced to quantify the saturation ratio decrease by water vapor consumption onto ice (Kuebbeler et al, 2014). Muench and Lohmann (2020) updated the water vapor consumption by ice, following the diffusional growth equation (Lohmann et al, 2016). The temporal change of the saturation ratio follows such that if the updraft is stronger than the water vapor consumption by pre-exisiting ice and heterogeneous INPs, then it may reach a suitable magnitude for homogeneous nucleation to occur.…”

Section: Model Descriptionmentioning

confidence: 99%

“…In general, the cirrus nucleation scheme follows an "energy-barrier" approach, with pre-existing ice and the most efficient INP, dust (in the default setup), consuming water vapor at a lower ice saturation ratio (S i ). An ice formation event in each mode can occur as either a threshold freezing process or as a continuous freezing process (Muench and Lohmann, 2020). The former is based on the original cirrus scheme by Kärcher et al (2006), whereby ice forms by a particular mode when its critical ice saturation ratio (S i,crit ) is reached.…”

Section: Model Descriptionmentioning

confidence: 99%

“…For dust immersion freezing, only 5 % of the total dust aerosol concentration from the aerosol module, HAM, act as INPs within the mode, following Gasparini and Lohmann (2016). Muench and Lohmann (2020) introduced the latter, continuous freezing process to account for the saturation-dependent activated fraction (AF) of INPs available for heterogeneous nucleation. We include deposition on insoluble accumulation and coarse size mode (Stier et al, 2005;Zhang et al, 2012;Tegen et al, 2019) dust particles as continuous freezing modes.…”

Section: Model Descriptionmentioning

confidence: 99%

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Cirrus cloud thinning using a more physically-based ice microphysics scheme in the ECHAM-HAM GCM

Tully

Neubauer

Omanovic

et al. 2021

Preprint

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Abstract. Cirrus cloud thinning (CCT) is a relatively new radiation management proposal to counteract anthropogenic climate warming by targeting Earth’s terrestrial radiation balance. The efficacy of this method was presented in several general circulation model (GCM) studies that showed widely varied radiative responses, originating in part from the differences in the representation of cirrus ice microphysics between the different GCMs. The recent implementation of a new, more physically based ice microphysics scheme (Predicted Particle Properties, P3) that abandons ice hydrometeor size class separation into the ECHAM-HAM GCM, coupled to a new approach for calculating cloud fractions that increases the relative humidity (RH) thresholds for cirrus cloud formation, motivated a reassessment of CCT efficacy. In this study, we first compared CCT sensitivity between the new cloud fraction approach and the original ECHAM-HAM cloud fraction approach. With the P3 scheme and the higher RH thresholds for cirrus cloud formation, we find a significant cooling response of −0.36 Wm−2 only for our simulation with a seeding particle concentration of 1 L−1, due mostly to rapid cloud adjustments. The most notable response is the reduction of the maximum global-mean net top-of-atmosphere (TOA) radiative anomalies from overseeding by more than 50 %, from 9.0 Wm−2 with the original cloud fraction approach, down to 4.3 Wm−2 using the new cloud fraction RH thresholds by avoiding artificial ice-cloud expansion upon ice nucleation. We attribute the large positive TOA anomalies to seeding particles overtaking both homogeneous nucleation and heterogeneous nucleation on mineral dust particles within cirrus clouds to produce more numerous and smaller ice crystals. This effect is amplified by longer ice residence times in clouds due to the more realistic, slower removal of ice via sedimentation in the P3 scheme. In an effort to avoid this overtaking effect of seeding particles, we increased the default critical ice saturation ratio (Si,seed) for ice nucleation on seeding particles from the default value of 1.05 to 1.35 in a second sensitivity test. With the higher Si,seed we eliminate overseeding and are able to produce cooling responses over a broader range of seeding particle concentrations, with the largest cooling of −0.32 Wm−2 for a seeding particle concentration of 10 L−1, which suggests that Si,seed is a key factor to consider for future CCT studies. However, the global-mean TOA anomalies contain high uncertainty. In response, we examined the TOA responses regionally and found that specific regions only show a small potential for targeted CCT, which is partially enhanced by using the larger Si,seed. Finally, in a seasonal analysis of TOA responses to CCT, we find that our results do not support the previous finding that high-latitude wintertime seeding is a feasible strategy to enhance CCT efficacy, as seeding in our model enhances the already positive cirrus longwave cloud radiative effect. Instead, our results show that summertime cooling occurs due to adjustments of lower-lying mixed-phase and liquid clouds. Therefore, we conclude that CCT is unlikely to act as a feasible climate intervention strategy on a global scale, and should be investigated further with higher-resolution studies in potential target regions and with studies dedicated to assessing potentially realistic seeding particle materials.

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“…In subtropical oceans where shallow convective clouds are prevalent, AOD is overestimated likely because precipitation from shallow convective clouds is only allowed if the clouds reach a certain thickness (Muench & Lohmann, 2020). Furthermore, black carbon and organic carbon concentrations are underestimated to some extent, which may be due to underestimated biomass burning emissions and cause to low AOD in biomass burning regions (Tegen et al, 2019).…”

Section: Accepted Articlementioning

confidence: 99%

Understanding Top‐of‐Atmosphere Flux Bias in the AeroCom Phase III Models: A Clear‐Sky Perspective

Liang

Myhre

et al. 2021

J Adv Model Earth Syst

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Over ocean, aerosol optical depth (AOD) bias contributes about 25% to the 60 • S-60 • N mean SW flux bias for the multi-model mean (MMM) result • Over land, AOD and land surface albedo biases contribute about 40% and 30% to the 60 • S-60 • N mean SW flux bias for the MMM result • Observation-based land surface albedo should be used by all models to accurately calculate the top-of-atmosphere shortwave fluxes

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Developing a Cloud Scheme With Prognostic Cloud Fraction and Two Moment Microphysics for ECHAM‐HAM

Cited by 25 publications

References 136 publications

Cold cloud microphysical process rates in a global chemistry–climate model

Cold cloud microphysical process rates in a global chemistry–climate model

Cirrus cloud thinning using a more physically-based ice microphysics scheme in the ECHAM-HAM GCM

Understanding Top‐of‐Atmosphere Flux Bias in the AeroCom Phase III Models: A Clear‐Sky Perspective

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