Cirrus cloud formation and ice supersaturated regions in a global climate model

Abstract. A statistical cirrus cloud scheme that accounts for mesoscale temperature perturbations is implemented in a coupled aerosol and atmospheric circulation model to better represent both subgrid-scale supersaturation and cloud formation. This new scheme treats the effects of aerosol on cloud formation and ice freezing in an improved manner, and both homogeneous freezing and heterogeneous freezing are included. The scheme is able to better simulate the observed probability distribution of relative humidity compared to the scheme that was implemented in an older version of the model. Heterogeneous ice nuclei (IN) are shown to decrease the frequency of occurrence of supersaturation, and improve the comparison with observations at 192 hPa. Homogeneous freezing alone can not reproduce observed ice crystal number concentrations at low temperatures (<205 K), but the addition of heterogeneous IN improves the comparison somewhat. Increases in heterogeneous IN affect both high level cirrus clouds and low level liquid clouds. Increases in cirrus clouds lead to a more cloudy and moist lower troposphere with less precipitation, effects which we associate with the decreased convective activity. The change in the net cloud forcing is not very sensitive to the change in ice crystal concentrations, but the change in the net radiative flux at the top of the atmosphere is still large because of changes in water vapor. Changes in the magnitude of the assumed mesoscale temperature perturbations by 25% alter the ice crystal number concentrations and the net radiative fluxes by an amount that is comparable to that from a factor of 10 change in the heterogeneous IN number concentrations. Further improvements on the representation of mesoscale temperature perturbations, heterogeneous IN and the competition between homogeneous freezing and heterogeneous freezing are needed.

Download Full-text

Global 3D modelling of Martian CO2 clouds

10.5194/egusphere-egu21-9457 ◽

2021 ◽

Author(s):

Christophe Mathé ◽

Anni Määttänen ◽

Joachim Audouard ◽

Constantino Listowski ◽

Ehouarn Millour ◽

...

Keyword(s):

Climate Model ◽

Global Climate ◽

Global Climate Model ◽

Martian Atmosphere ◽

Cloud Formation ◽

Polar Regions ◽

Northern Latitudes ◽

1D Model ◽

Mesospheric Clouds ◽

Microphysical Processes

In the Martian atmosphere, carbon dioxide (CO2) clouds have been revealed by numerous instruments around Mars from the beginning of the XXI century. These observed clouds can be distinguished by two kinds involving different formation processes: those formed during the winter in polar regions located in the troposphere, and those formed during the Martian year at low- and mid-northern latitudes located in the mesosphere (M&#228;&#228;att&#228;nen et al, 2013). Microphysical processes of the formation of these clouds are still not fully understood. However, modeling studies revealed processes necessary for their formation: the requirement of waves that perturb the atmosphere leading to a temperature below the condensation of CO2 (transient planetary waves for tropospheric clouds (Kuroda et al., 20123), thermal tides (Gonzalez-Galindo et al., 2011) and gravity waves for mesospheric clouds (Spiga et al., 2012)). In the last decade, a state-of-the-art microphysical column (1D) model for CO2 clouds in a Martian atmosphere was developed at Laboratoire Atmosph&#232;res, Observations Spatiales (LATMOS) (Listowski et al., 2013, 2014). We use our full microphysical model of CO2 cloud formation to investigate the occurrence of these CO2 clouds by coupling it with the Global Climate Model (GCM) of the Laboratoire de M&#233;t&#233;orologie Dynamique (LMD) (Forget et al., 1999). We recently activated the radiative impact of CO2 clouds in the atmosphere. Last modeling results on Martian CO2 clouds properties and their impacts on the atmosphere will be presented and be compared to observational data.

Download Full-text

Bacteria in the ECHAM5-HAM global climate model

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-8645-2012 ◽

2012 ◽

Vol 12 (18) ◽

pp. 8645-8661 ◽

Cited By ~ 48

Author(s):

A. Sesartic ◽

U. Lohmann ◽

T. Storelvmo

Keyword(s):

Active Sites ◽

Climate Model ◽

Global Climate ◽

Global Climate Model ◽

Ice Nucleation ◽

Cloud Formation ◽

Liquid Water Path ◽

Water Path ◽

Ice Nuclei ◽

Ice Water

Abstract. Some bacteria are among the most active ice nuclei found in nature due to the ice nucleation active proteins on their surface, which serve as active sites for ice nucleation. Their potential impact on clouds and precipitation is not well known and needs to be investigated. Bacteria as a new aerosol species were introduced into the global climate model (GCM) ECHAM5-HAM. The inclusion of bacteria acting as ice nuclei in a GCM leads to only minor changes in cloud formation and precipitation on a global level, however, changes in the liquid water path and ice water path are simulated, specifically in the boreal regions where tundra and forests act as sources of bacteria. Although bacteria contribute to heterogeneous freezing, their impact is reduced by their low numbers compared to other heterogeneous IN. This result confirms the outcome of several previous studies.

Download Full-text

Cirrus clouds in a global climate model with a statistical cirrus cloud scheme

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-16607-2009 ◽

2009 ◽

Vol 9 (4) ◽

pp. 16607-16682 ◽

Cited By ~ 3

Author(s):

M. Wang ◽

J. E. Penner

Keyword(s):

Climate Models ◽

Climate Model ◽

Global Climate ◽

Global Climate Model ◽

Circulation Model ◽

Global Climate Models ◽

Cirrus Clouds ◽

Cirrus Cloud ◽

Ice Crystal ◽

Low Level

Abstract. A statistical cirrus cloud scheme that accounts for mesoscale temperature perturbations is implemented into a coupled aerosol and atmospheric circulation model to better represent both cloud fraction and subgrid-scale supersaturation in global climate models. This new scheme is able to better simulate the observed probability distribution of relative humidity than the scheme that was implemented in an older version of the model. Heterogeneous ice nuclei (IN) are shown to affect not only high level cirrus clouds through their effect on ice crystal number concentration but also low level liquid clouds through the moistening effect of settling and evaporating ice crystals. As a result, the change in the net cloud forcing is not very sensitive to the change in ice crystal concentrations associated with heterogeneous IN because changes in high cirrus clouds and low level liquid clouds tend to cancel. Nevertheless, the change in the net radiative flux at the top of the atmosphere due to changes in IN is still large because of changes in the greenhouse effect of water vapor caused by the changes in ice crystal number concentrations. Changes in the magnitude of the assumed mesoscale temperature perturbations by 25% alter the ice crystal number concentrations and radiative fluxes by an amount that is similar to that from a factor of 10 change in the heterogeneous IN number concentrations.

Download Full-text

Freezing thresholds and cirrus cloud formation mechanisms inferred from in situ measurements of relative humidity

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-3-3267-2003 ◽

2003 ◽

Vol 3 (3) ◽

pp. 3267-3299 ◽

Cited By ~ 4

Author(s):

W. Haag ◽

B. Kärcher ◽

J. Ström ◽

A. Minikin ◽

U. Lohmann ◽

...

Keyword(s):

Relative Humidity ◽

Large Scale ◽

Climate Model ◽

Global Climate Model ◽

In Situ Measurements ◽

Cirrus Clouds ◽

Cloud Formation ◽

Formation Mechanisms ◽

Cirrus Cloud

Abstract. Factors controlling the distribution of relative humidity above ice saturation in the upper troposphere and lower stratosphere in the presence of cirrus clouds are examined with the help of microphysical trajectory simulations using a box model. Our findings are related to results from recent field campaigns and global model studies. We suggest that the relative humidities at which ice crystals form in the atmosphere can be inferred from in situ measurements of water vapor and temperature close to, but outside of, cirrus clouds. The comparison with similar measurements performed inside cirrus clouds provides a clue to freezing mechanisms active in cirrus. The comparison with field data reveals distinct interhemispheric differences in cirrus cloud freezing thresholds. Combining the present findings with recent results addressing the frequency distributions of updraft speeds and cirrus ice crystal number densities (Kärcher and Ström, 2993} provides evidence for the existence of complex heterogeneous freezing mechanisms in cirrus, at least in the polluted northern hemisphere, and further emphasizes the key role of gravity wave-induced dynamical variability in vertical air motion at the mesoscale. The key features of distributions of upper tropospheric relative humidity simulated by a global climate model are shown to be in general agreement with both, microphysical simulations and field observations, delineating a feasible method to include and validate ice supersaturation in other large-scale models of the atmosphere, in particular chemistry-transport and weather forecast models.

Download Full-text

Global Climate Model Simulations of Natural Aerosols over the Southern Ocean

10.5194/egusphere-egu21-195 ◽

2021 ◽

Author(s):

Yusuf Bhatti ◽

Laura Revell ◽

Adrian McDonald ◽

Jonny Willaims

Keyword(s):

Southern Ocean ◽

Dimethyl Sulfide ◽

Climate Model ◽

Global Climate ◽

Global Climate Model ◽

Cloud Formation ◽

Sulfate Aerosols ◽

Climate Model Simulations ◽

Aerosol Cloud Interactions ◽

The Impact

We studied sulfate aerosols over the Southern Ocean using the atmosphere-only climate model HadGEM3-GA7.1. The model contains biases in the aerosol seasonal variability over the Southern Ocean (40&#176;S to 60&#176;S), which cascade to uncertainties in aerosol-cloud interactions. Aerosols over the Southern Ocean are primarily natural in origin, such as sea spray aerosol and sulfate aerosol formed by phytoplankton-produced dimethyl sulfide (DMS).The current sulfate chemistry scheme implemented in the model simplifies the oxidation pathways for DMS, which has been identified as a major source of the seasonal bias present. The simulations performed here incorporate a comprehensive sulfate scheme in both the gas and aqueous-phase. An intermediate complexity biogeochemical dynamic model, MEDUSA, simulated a global climatology of seawater DMS, which is compared with a seawater DMS observational dataset from 2011. We compared the seasonality of sulfate aerosols over the Southern Ocean, and the global distribution using the two seawater DMS climatologies. Simulated aerosols over the Southern Ocean were evaluated against satellite and in-situ observations. The results show the impact of seawater DMS on sulfate aerosols and their influence on cloud formation.

Download Full-text

Cirrus Cloud Microphysical Properties and Aerosol Indirect Effects using Airborne Observations and a Global Climate Model

10.31979/etd.t5pv-7w26 ◽

2020 ◽

Author(s):

Ryan Patnaude

Keyword(s):

Indirect Effects ◽

Climate Model ◽

Global Climate ◽

Global Climate Model ◽

Cirrus Cloud ◽

Aerosol Indirect Effects ◽

Microphysical Properties

Download Full-text

Bacteria in the ECHAM5-HAM global climate model

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-1457-2011 ◽

2011 ◽

Vol 11 (1) ◽

pp. 1457-1488 ◽

Cited By ~ 11

Author(s):

A. Sesartic ◽

U. Lohmann ◽

T. Storelvmo

Keyword(s):

Active Sites ◽

Climate Model ◽

Global Climate ◽

Global Climate Model ◽

Ice Nucleation ◽

Cloud Formation ◽

Liquid Water Path ◽

Water Path ◽

Ice Nuclei ◽

Ice Water

Abstract. Bacteria are the most active naturally occuring ice nuclei (IN) due to the ice nucleation active proteins on their surface, which serve as active sites for ice nucleation. Their potential impact on clouds and precipitation is not well known and needs to be investigated. Bacteria as a new aerosol species were introduced into the global climate model (GCM) ECHAM5-HAM. The inclusion of bacteria acting as IN in a GCM leads to only minor changes in cloud formation and precipitation on a global level, however, changes in the liquid water path and ice water path can be observed, specifically in the boreal regions where tundra and forests act as sources of bacteria.

Download Full-text