scholarly journals EPIC simulations of Neptune’s dark spots using an active cloud microphysical model

2020 ◽  
Vol 496 (4) ◽  
pp. 4760-4768
Author(s):  
Nathan Hadland ◽  
Ramanakumar Sankar ◽  
Raymond Paul LeBeau ◽  
Csaba Palotai
Keyword(s):  
Northern Hemisphere ◽  
General Circulation ◽  
Large Scale ◽  
Dynamic Properties ◽  
Circulation Model ◽  
Cloud Microphysics ◽  
Cloud Formation ◽  
Explicit Calculation ◽  
Dark Spot ◽  
Vapour Density

ABSTRACT The Great Dark Spot (GDS-89) observed by Voyager 2 was the first of several large-scale vortices observed on Neptune, the most recent of which was observed in 2018 in the Northern hemisphere (NDS-2018). Ongoing observations of these features are constraining cloud formation, drift, shape oscillations, and other dynamic properties. In order to effectively model these characteristics, an explicit calculation of methane cloud microphysics is needed. Using an updated version of the Explicit Planetary Isentropic Coordinate General Circulation Model (EPIC GCM) and its active cloud microphysics module to account for the condensation of methane, we investigate the evolution of large-scale vortices on Neptune. We model the effect of methane deep abundance and cloud formation on vortex stability and dynamics. In our simulations, the vortex shows a sharp contrast in methane vapour density inside compared to outside the vortex. Methane vapour column density is analogous to optical depth and provides a more consistent tracer to track the vortex, so we use that variable over potential vorticity. We match the meridional drift rate of the GDS and gain an initial insight into the evolution of vortices in the Northern hemisphere, such as the NDS-2018.

scholarly journals Global anthropogenic aerosol effects on convective clouds in ECHAM5-HAM

2008 ◽  
Vol 8 (7) ◽  
pp. 2115-2131 ◽  
Author(s):  
U. Lohmann
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Hydrological Cycle ◽  
Circulation Model ◽  
Cloud Microphysics ◽  
Convective Precipitation ◽  
Anthropogenic Aerosol ◽  
Convective Clouds ◽  
Double Moment ◽  
Aerosol Effects

Abstract. Aerosols affect the climate system by changing cloud characteristics in many ways. They act as cloud condensation and ice nuclei and may have an influence on the hydrological cycle. Here we investigate aerosol effects on convective clouds by extending the double-moment cloud microphysics scheme developed for stratiform clouds, which is coupled to the HAM double-moment aerosol scheme, to convective clouds in the ECHAM5 general circulation model. This enables us to investigate whether more, and smaller cloud droplets suppress the warm rain formation in the lower parts of convective clouds and thus release more latent heat upon freezing, which would then result in more vigorous convection and more precipitation. In ECHAM5, including aerosol effects in large-scale and convective clouds (simulation ECHAM5-conv) reduces the sensitivity of the liquid water path increase with increasing aerosol optical depth in better agreement with observations and large-eddy simulation studies. In simulation ECHAM5-conv with increases in greenhouse gas and aerosol emissions since pre-industrial times, the geographical distribution of the changes in precipitation better matches the observed increase in precipitation than neglecting microphysics in convective clouds. In this simulation the convective precipitation increases the most suggesting that the convection has indeed become more vigorous.

scholarly journals Effects of Cloud Microphysics on Tropical Atmospheric Hydrologic Processes and Intraseasonal Variability

2005 ◽  
Vol 18 (22) ◽  
pp. 4731-4751 ◽  
Author(s):  
K. M. Lau ◽  
H. T. Wu ◽  
Y. C. Sud ◽  
G. K. Walker
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Water Cycle ◽  
Deep Convection ◽  
Intraseasonal Variability ◽  
Lower Troposphere ◽  
Circulation Model ◽  
Cloud Microphysics ◽  
Hydrologic Processes ◽  
Warm Rain

Abstract The sensitivity of tropical atmospheric hydrologic processes to cloud microphysics is investigated using the NASA Goddard Earth Observing System (GEOS) general circulation model (GCM). Results show that a faster autoconversion rate leads to (a) enhanced deep convection in the climatological convective zones anchored to tropical land regions; (b) more warm rain, but less cloud over oceanic regions; and (c) an increased convective-to-stratiform rain ratio over the entire Tropics. Fewer clouds enhance longwave cooling and reduce shortwave heating in the upper troposphere, while more warm rain produces more condensation heating in the lower troposphere. This vertical differential heating destabilizes the tropical atmosphere, producing a positive feedback resulting in more rain and an enhanced atmospheric water cycle over the Tropics. The feedback is maintained via secondary circulations between convective tower and anvil regions (cold rain), and adjacent middle-to-low cloud (warm rain) regions. The lower cell is capped by horizontal divergence and maximum cloud detrainment near the freezing–melting (0°C) level, with rising motion (relative to the vertical mean) in the warm rain region connected to sinking motion in the cold rain region. The upper cell is found above the 0°C level, with induced subsidence in the warm rain and dry regions, coupled to forced ascent in the deep convection region. It is that warm rain plays an important role in regulating the time scales of convective cycles, and in altering the tropical large-scale circulation through radiative–dynamic interactions. Reduced cloud–radiation feedback due to a faster autoconversion rate results in intermittent but more energetic eastward propagating Madden–Julian oscillations (MJOs). Conversely, a slower autoconversion rate, with increased cloud radiation produces MJOs with more realistic westward-propagating transients embedded in eastward-propagating supercloud clusters. The implications of the present results on climate change and water cycle dynamics research are discussed.

The Tropospheric Response to Tropical and Subtropical Zonally Asymmetric Torques: Analytical and Idealized Numerical Model Results

2012 ◽  
Vol 69 (1) ◽  
pp. 214-235 ◽  
Author(s):  
Tiffany A. Shaw ◽  
William R. Boos
Keyword(s):  
Temperature Gradient ◽  
Northern Hemisphere ◽  
General Circulation ◽  
Large Scale ◽  
Critical Line ◽  
Circulation Model ◽  
General Circulation Models ◽  
Kelvin Wave ◽  
Meridional Temperature Gradient ◽  
Poleward Shift

Abstract The tropospheric response to prescribed tropical and subtropical zonally asymmetric torques, which can be considered as idealizations of vertical momentum transfers by orographic gravity waves or convection, is investigated. The linear analytical Gill model response to westward upper-tropospheric torques is compared to the response to a midtropospheric heating, which is a familiar point of reference. The response to an equatorial torque projects onto a Kelvin wave response to the east that is of opposite sign to the response to the east of the heating at upper levels. In contrast, the torque and heating both produce Rossby gyres of the same sign to the west of the forcing and the zonal-mean streamfunction responses are identical. When the forcings are shifted into the Northern Hemisphere, the streamfunction responses have opposite signs: there is upwelling in the Southern (Northern) Hemisphere in response to the torque (heating). The nonlinear response to westward torques was explored in idealized general circulation model experiments. In the absence of a large-scale meridional temperature gradient, the response to an equatorial torque was confined to the tropics and was qualitatively similar to the linear solutions. When the torque was moved into the subtropics, the vorticity budget response was similar to a downward control–type balance in the zonal mean. In the presence of a meridional temperature gradient, the response to an equatorial torque involved a poleward shift of the midlatitude tropospheric jet and Ferrel cell. The response in midlatitudes was associated with a poleward shift of the regions of horizontal eddy momentum flux convergence, which coincided with a shift in the upper-tropospheric critical line for baroclinic waves. The shift in the critical line was caused (in part) by the zonal wind response to the prescribed torque, suggesting a possible cause of the response in midlatitudes. Overall, this hierarchy of analytical and numerical results highlights robust aspects of the response to tropical and subtropical zonally asymmetric torques and represents the first step toward understanding the response in fully comprehensive general circulation models.

scholarly journals Introduction of prognostic rain in ECHAM5: design and single column model simulations

2008 ◽  
Vol 8 (11) ◽  
pp. 2949-2963 ◽  
Author(s):  
R. Posselt ◽  
U. Lohmann
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Cloud Microphysics ◽  
Rain Water ◽  
Time Step ◽  
Surface Precipitation ◽  
Column Model ◽  
Single Column ◽  
Single Column Model

Abstract. Prognostic equations for the rain mass mixing ratio and the rain drop number concentration are introduced into the large-scale cloud microphysics parameterization of the ECHAM5 general circulation model (ECHAM5-PROG). To this end, a rain flux from one level to the next with the appropriate fall speed is introduced. This maintains rain water in the atmosphere to be available for the next time step. Rain formation in ECHAM5-PROG is, therefore, less dependent on the autoconversion rate than the standard ECHAM5 but shifts the emphasis towards the accretion rates in accordance with observations. ECHAM5-PROG is tested and evaluated with Single Column Model (SCM) simulations for two cases: the marine stratocumulus study EPIC (October 2001) and the continental mid-latitude ARM Cloud IOP (shallow frontal cloud case – March 2000). In case of heavy precipitation events, the prognostic equations for rain hardly affect the amount and timing of precipitation at the surface in different SCM simulations because heavy rain depends mainly on the large-scale forcing. In case of thin, drizzling clouds (i.e., stratocumulus), surface precipitation is sensitive to the number of sub-time steps used in the prognostic rain scheme. Cloud microphysical quantities, such as cloud liquid and rain water within the atmosphere, are sensitive to the number of sub-time steps in both considered cases. This results from the decreasing autoconversion rate and increasing accretion rate.

scholarly journals Introduction of prognostic rain in ECHAM5: design and Single Column Model simulations

2007 ◽  
Vol 7 (5) ◽  
pp. 14675-14706 ◽  
Author(s):  
R. Posselt ◽  
U. Lohmann
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Cloud Microphysics ◽  
Rain Water ◽  
Time Step ◽  
Surface Precipitation ◽  
Column Model ◽  
Single Column ◽  
Single Column Model

Abstract. Prognostic equations for the rain mass mixing ratio and the rain drop number concentration are introduced into the large-scale cloud microphysics parameterization of the ECHAM5 general circulation model (ECHAM5-RAIN). For this a rain flux from one level to the next with the appropriate fall speed is introduced. This maintains rain water in the atmosphere to be available for the next time step. Rain formation in ECHAM5-RAIN is, therefore, less dependent on the autoconversion rate than the standard ECHAM5 but shifts the emphasis towards the accretion rates in accordance with observations. ECHAM5-RAIN is tested and evaluated with two cases: the continental mid-latitude ARM Cloud IOP (shallow frontal cloud case – March 2000) and EPIC (a marine stratocumulus study – October 2001). The prognostic equations for rain hardly affect the amount and timing of precipitation at the surface in different Single Column Model (SCM) simulations for heavy precipitating clouds because heavy rain depends mainly on the large-scale forcing. In case of thin, drizzling clouds (i.e., stratocumulus), an increase in surface precipitation is caused by more sub-time steps used in the prognostic rain scheme until convergence is reached. Cloud microphysical quantities, such as liquid and rain water, are more sensitive to the number of sub-time steps for light precipitation. This results from the decreasing autoconversion rate and increasing accretion rate.

Modeling Water Vapor and Clouds as Passive Tracers in an Idealized GCM

2018 ◽  
Vol 31 (2) ◽  
pp. 775-786 ◽  
Author(s):  
Yi Ming ◽  
Isaac M. Held
Keyword(s):  
Water Vapor ◽  
General Circulation ◽  
Large Scale ◽  
Probability Distributions ◽  
Water Vapor Pressure ◽  
Substantial Reduction ◽  
Lower Troposphere ◽  
Circulation Model ◽  
Cloud Microphysics ◽  
Cloud Fraction

This paper introduces an idealized general circulation model (GCM) in which water vapor and clouds are tracked as tracers, but are not allowed to affect circulation through either latent heat release or cloud radiative effects. The cloud scheme includes an explicit treatment of cloud microphysics and diagnoses cloud fraction from a prescribed subgrid distribution of total water. The model is capable of qualitatively capturing many large-scale features of water vapor and cloud distributions outside of the boundary layer and deep tropics. The subtropical dry zones, midlatitude storm tracks, and upper-tropospheric cirrus are simulated reasonably well. The inclusion of cloud microphysics (namely rain re-evaporation) has a modest but significant effect of moistening the lower troposphere in this model. When being subjected to a uniform fractional increase of saturated water vapor pressure, the model produces little change in cloud fraction. A more realistic perturbation, which considers the nonlinearity of the Clausius–Clapeyron relation and spatial structure of CO2-induced warming, results in a substantial reduction in the free-tropospheric cloud fraction. This is reconciled with an increase of relative humidity by analyzing the probability distributions of both quantities, and may help explain partly similar decreases in cloud fraction in full GCMs. The model provides a means to isolate individual processes or model components for studying their influences on cloud simulation in the extratropical free troposphere.

The General Circulation and Robust Relative Humidity

2006 ◽  
Vol 19 (24) ◽  
pp. 6278-6290 ◽  
Author(s):  
S. C. Sherwood ◽  
C. L. Meyer
Keyword(s):  
Relative Humidity ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Cloud Microphysics ◽  
Homogeneous State ◽  
Surface Warming ◽  
Westerly Jet ◽  
Community Atmosphere Model ◽  
Microphysical Processes

Abstract The sensitivity of free-tropospheric relative humidity to cloud microphysics and dynamics is explored using a simple 2D humidity model and various configurations of the National Center for Atmospheric Research (NCAR) Community Atmosphere Model version 3 (CAM3) atmospheric general circulation model (AGCM). In one configuration the imposed surface temperatures and radiative perturbations effectively eliminated the Hadley and Walker circulations and the main westerly jet, creating instead a homogeneous “boiling kettle” world in low and midlatitudes. A similarly homogeneous state was created in the 2D model by rapid horizontal mixing. Relative humidity ℛ simulated by the AGCM was insensitive to surface warming. Doubling a parameter governing cloud water reevaporation increased tropical mean ℛ near the midtroposphere by about 4% with a realistic circulation, but by more than 10% in the horizontally homogeneous states. This was consistent in both models. AGCM microphysical sensitivity decreased in the upper troposphere, and vanished outside the Tropics. Convective organization by the general circulation evidently makes relative humidity much more robust to microphysical details by concentrating the rainfall in moist environments. Models that fail to capture this will overestimate the microphysical sensitivity of humidity. Based on these results, the uncertainty in the strength of the water vapor feedback associated with cloud microphysical processes seems unlikely to exceed a few percent. This does not include uncertainties associated with large-scale dynamics or cloud radiative effects, which cannot be quantified, although radical CAM3 circulation changes reported here had surprisingly little impact on simulated relative humidity.

scholarly journals Bacteria in the global atmosphere – Part 2: Modeling of emissions and transport between different ecosystems

2009 ◽  
Vol 9 (23) ◽  
pp. 9281-9297 ◽  
Author(s):  
S. M. Burrows ◽  
T. Butler ◽  
P. Jöckel ◽  
H. Tost ◽  
A. Kerkweg ◽  
...  
Keyword(s):  
Seasonal Variation ◽  
Residence Time ◽  
General Circulation ◽  
Bacterial Species ◽  
Circulation Model ◽  
Cloud Condensation Nucleus ◽  
Cloud Formation ◽  
Emission Region ◽  
Culturable Bacteria ◽  
Bacterial Cells

Abstract. Bacteria are constantly being transported through the atmosphere, which may have implications for human health, agriculture, cloud formation, and the dispersal of bacterial species. We simulate the global transport of bacteria, represented as 1 μm and 3 μm diameter spherical solid particle tracers in a general circulation model. We investigate factors influencing residence time and distribution of the particles, including emission region, cloud condensation nucleus activity and removal by ice-phase precipitation. The global distribution depends strongly on the assumptions made about uptake into cloud droplets and ice. The transport is also affected, to a lesser extent, by the emission region, particulate diameter, and season. We find that the seasonal variation in atmospheric residence time is insufficient to explain by itself the observed seasonal variation in concentrations of particulate airborne culturable bacteria, indicating that this variability is mainly driven by seasonal variations in culturability and/or emission strength. We examine the potential for exchange of bacteria between ecosystems and obtain rough estimates of the flux from each ecosystem by using a maximum likelihood estimation technique, together with a new compilation of available observations described in a companion paper. Globally, we estimate the total emissions of bacteria-containing particles to the atmosphere to be 7.6×1023–3.5×1024 a−1, originating mainly from grasslands, shrubs and crops. We estimate the mass of emitted bacteria- to be 40–1800 Gg a−1, depending on the mass fraction of bacterial cells in the particles. In order to improve understanding of this topic, more measurements of the bacterial content of the air and of the rate of surface-atmosphere exchange of bacteria will be necessary. Future observations in wetlands, hot deserts, tundra, remote glacial and coastal regions and over oceans will be of particular interest.

scholarly journals Towards a regional ocean forecasting system for the IBI (Iberia-Biscay-Ireland area): developments and improvements within the ECOOP project framework

Ocean Science ◽  
2012 ◽  
Vol 8 (2) ◽  
pp. 143-159 ◽  
Author(s):  
S. Cailleau ◽  
J. Chanut ◽  
J.-M. Lellouche ◽  
B. Levier ◽  
C. Maraldi ◽  
...  
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Vertical Mixing ◽  
Circulation Model ◽  
Storm Surges ◽  
Ocean General Circulation Model ◽  
Tidal Mixing ◽  
Basin Scale ◽  
Forecasting System ◽  
Ocean Forecasting

Abstract. The regional ocean operational system remains a key element in downscaling from large scale (global or basin scale) systems to coastal ones. It enables the transition between systems in which the resolution and the resolved physics are quite different. Indeed, coastal applications need a system to predict local high frequency events (inferior to the day) such as storm surges, while deep sea applications need a system to predict large scale lower frequency ocean features. In the framework of the ECOOP project, a regional system for the Iberia-Biscay-Ireland area has been upgraded from an existing V0 version to a V2. This paper focuses on the improvements from the V1 system, for which the physics are close to a large scale basin system, to the V2 for which the physics are more adapted to shelf and coastal issues. Strong developments such as higher regional physics resolution in the NEMO Ocean General Circulation Model for tides, non linear free surface and adapted vertical mixing schemes among others have been implemented in the V2 version. Thus, regional thermal fronts due to tidal mixing now appear in the latest version solution and are quite well positioned. Moreover, simulation of the stratification in shelf areas is also improved in the V2.

scholarly journals Multi-model dynamic climate emulator for solar geoengineering

2016 ◽  
Author(s):  
Douglas G. MacMartin ◽  
Ben Kravitz
Keyword(s):  
Sea Ice ◽  
Northern Hemisphere ◽  
General Circulation ◽  
Circulation Model ◽  
Nonlinear Effects ◽  
Accurate Estimate ◽  
Natural Variability ◽  
Sea Ice Extent ◽  
Temperature And Precipitation ◽  
Solar Geoengineering

Abstract. Climate emulators trained on existing simulations can be used to project the climate effects that would result from different possible future pathways of anthropogenic forcing, without relying on general circulation model (GCM) simulations for every possible pathway. We extend this idea to include different amounts of solar geoengineering in addition to different pathways of green-house gas concentrations by training emulators from a multi-model ensemble of simulations from the Geoengineering Model Intercomparison Project (GeoMIP). The emulator is trained on the abrupt 4 x CO2 and a compensating solar reduction simulation (G1), and evaluated by comparing predictions against a simulated 1 % per year CO2 increase and a similarly smaller solar reduction (G2). We find reasonable agreement in most models for predicting changes in temperature and precipitation (including regional effects), and annual-mean Northern hemisphere sea ice extent, with the difference between simulation and prediction typically smaller than natural variability. This verifies that the linearity assumption used in constructing the emulator is sufficient for these variables over the range of forcing considered. Annual-minimum Northern hemisphere sea ice extent is less-well predicted, indicating the limits of the linearity assumption. For future pathways involving relatively small forcing from solar geoengineering, the errors introduced from nonlinear effects may be smaller than the uncertainty due to natural variability, and the emulator prediction may be a more accurate estimate of the forced component of the models' response than an actual simulation would be.

Sign in / Sign up

Export Citation Format

Share Document