Events (Upcoming & Past)

Past MMM Events

William SkamarockNCAR/MMM 

One of the unsolved questions in atmospheric dynamics concerns the energetics responsible for the horizontal wavenumber k^(-5/3) scaling observed in the mesoscale portion of the atmospheric kinetic energy (KE) spectrum.  Model spectra qualitatively reproduce the observations-based spectrum in both the synoptic-scale k^(-3) and mesoscale k^(-5/3) regions, and given the limitations of the observations, modeling-based studies have become the primary approach for examining the mesoscale dynamics of the spectrum.  We are computing atmospheric spectra for global NWP forecasts using the atmospheric component of the Model for Prediction Across Scales (MPAS) to study these dynamics.  As in past studies, we find a mesoscale region in the model spectrum when resolution is sufficiently fine.  The first part of the present study examines the accuracy of model solutions, where we find that typical model configurations produce solutions that are significantly under-resolved vertically as revealed in convergence test results for KE spectra and examination of inertia gravity wave structure.  The second part of this study examines KE dissipation and its associated dynamics.  The mesoscale region is thought to be characterized as possessing a net downscale energy cascade, and the dynamics in the regions of energy dissipation should play a role in the downscale cascade.   Understanding these dynamics should help test existing theories for the mesoscale KE spectrum.  We will present results illustrating these points,  and we will discuss the implications of these results for current theories for the mesoscale KE spectrum.  We will also discuss the implications for atmospheric modeling applications in weather and climate given that current operational weather and climate model configurations do not resolve well the mesoscale KE, particularly in the upper troposphere and lower stratosphere.

Refreshments: 3:15 pm

Building:
Room Number: 
1022
Type of event:
Will this event be webcast to the public by NCAR|UCAR?: 
Calendar Timing: 
Friday, December 8, 2017 - 5:30am to 6:30am

William Skamarock
NCAR/MMM 

One of the unsolved questions in atmospheric dynamics concerns the energetics responsible for the horizontal wavenumber k^(-5/3) scaling observed in the mesoscale portion of the atmospheric kinetic energy (KE) spectrum.  Model spectra qualitatively reproduce the observations-based spectrum in both the synoptic-scale k^(-3) and mesoscale k^(-5/3) regions, and given the limitations of the observations, modeling-based studies have become the primary approach for examining the mesoscale dynamics of the spectrum.  We are computing atmospheric spectra for global NWP forecasts using the atmospheric component of the Model for Prediction Across Scales (MPAS) to study these dynamics.  As in past studies, we find a mesoscale region in the model spectrum when resolution is sufficiently fine.  The first part of the present study examines the accuracy of model solutions, where we find that typical model configurations produce solutions that are significantly under-resolved vertically as revealed in convergence test results for KE spectra and examination of inertia gravity wave structure.  The second part of this study examines KE dissipation and its associated dynamics.  The mesoscale region is thought to be characterized as possessing a net downscale energy cascade, and the dynamics in the regions of energy dissipation should play a role in the downscale cascade.   Understanding these dynamics should help test existing theories for the mesoscale KE spectrum.  We will present results illustrating these points,  and we will discuss the implications of these results for current theories for the mesoscale KE spectrum.  We will also discuss the implications for atmospheric modeling applications in weather and climate given that current operational weather and climate model configurations do not resolve well the mesoscale KE, particularly in the upper troposphere and lower stratosphere.

Refreshments: 3:15 pm

First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, December 7, 2017 - 3:30pm to 4:30pm

Raymond A. ShawAtmospheric Sciences Program Michigan Technological University 

Aerosol particles, such as sea salt, dust and anthropogenic pollution, influence the optical properties of clouds and the tendency of a cloud to form precipitation through droplet collisions. We have investigated cloud droplet growth in a turbulent environment under varying levels of aerosol concentration. The results reveal a surprising role of turbulence in cloud droplet growth that leads to two regimes: a polluted cloud regime in which thermodynamic conditions are rather uniform and cloud droplet sizes are similar, and a clean cloud regime in which thermodynamic conditions are highly variable and cloud droplet sizes are very diverse. The narrowing of droplet size range under polluted conditions introduces a new stabilizing factor by which increased aerosol concentration can suppress precipitation and enhance cloud brightness. 

Cloud droplet growth in a turbulent environment is studied by creating turbulent moist Rayleigh-Benard convection in a laboratory chamber (the Pi Chamber). Cloud formation is achieved by injecting aerosols into the water-supersaturated environment created by the isobaric mixing of saturated air at different temperatures. In steady state, the injection and activation of aerosol particles to form cloud droplets is balanced by cloud droplet growth through vapor condensation and loss by gravitational settling. A range of steady-state cloud droplet number concentrations is achieved by supplying aerosols at different rates. As steady-state droplet number concentration is decreased the mean droplet size increases as expected, but also the width of the size distribution increases. This increase in the width is associated with larger supersaturation fluctuations due to the slow droplet microphysical response (sink of the water vapor) compared to the fast turbulent mixing (source of the water vapor). The boundary between the two regimes can be identified with a cloud Damkoehler number of order unity.

Thursday, 16 November 2017, 3:30 PM Refreshments:  3:15 PM

Building:
Room Number: 
1022
Type of event:
Will this event be webcast to the public by NCAR|UCAR?: 
Calendar Timing: 
Friday, November 17, 2017 - 5:30am to 6:30am

Raymond A. Shaw
Atmospheric Sciences Program
Michigan Technological University 

Aerosol particles, such as sea salt, dust and anthropogenic pollution, influence the optical properties of clouds and the tendency of a cloud to form precipitation through droplet collisions. We have investigated cloud droplet growth in a turbulent environment under varying levels of aerosol concentration. The results reveal a surprising role of turbulence in cloud droplet growth that leads to two regimes: a polluted cloud regime in which thermodynamic conditions are rather uniform and cloud droplet sizes are similar, and a clean cloud regime in which thermodynamic conditions are highly variable and cloud droplet sizes are very diverse. The narrowing of droplet size range under polluted conditions introduces a new stabilizing factor by which increased aerosol concentration can suppress precipitation and enhance cloud brightness. 

Cloud droplet growth in a turbulent environment is studied by creating turbulent moist Rayleigh-Benard convection in a laboratory chamber (the Pi Chamber). Cloud formation is achieved by injecting aerosols into the water-supersaturated environment created by the isobaric mixing of saturated air at different temperatures. In steady state, the injection and activation of aerosol particles to form cloud droplets is balanced by cloud droplet growth through vapor condensation and loss by gravitational settling. A range of steady-state cloud droplet number concentrations is achieved by supplying aerosols at different rates. As steady-state droplet number concentration is decreased the mean droplet size increases as expected, but also the width of the size distribution increases. This increase in the width is associated with larger supersaturation fluctuations due to the slow droplet microphysical response (sink of the water vapor) compared to the fast turbulent mixing (source of the water vapor). The boundary between the two regimes can be identified with a cloud Damkoehler number of order unity.

Thursday, 16 November 2017, 3:30 PM
Refreshments:  3:15 PM

First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, November 16, 2017 - 3:30pm to 4:30pm

Richard Rotunno NCAR/MMM 

From the point of view of the shallow-water equations (SWE), the hydraulic jump is a discontinuity in fluid-layer depth and velocity at which kinetic energy is dissipated. To provide an understanding of the origin and internal dynamics of the hydraulic jump, three-dimensional numerical solutions of the Navier-Stokes Equations (NSE) are carried out alongside SWE solutions for nearly identical physical initial-value problems. Analysis of the solutions to the initial-value problem shows that the tendency to form either the lee-side height/velocity discontinuity in the SWE, or the overturning density interface in the NSE, is a feature of inviscid, nonturbulent fluid dynamics. Dissipative turbulent processes associated with the lee-side hydraulic jump are a consequence of the inviscid fluid dynamics that initiate and maintain the locally unstable conditions. Implications for the modeling of atmospheric mountain waves and lee vortices are discussed.

Refreshments:  3:15 PM

Building:
Room Number: 
1022
Type of event:
Will this event be webcast to the public by NCAR|UCAR?: 
Calendar Timing: 
Friday, November 10, 2017 - 5:30am to 6:30am

Richard Rotunno
NCAR/MMM 

From the point of view of the shallow-water equations (SWE), the hydraulic jump is a discontinuity in fluid-layer depth and velocity at which kinetic energy is dissipated. To provide an understanding of the origin and internal dynamics of the hydraulic jump, three-dimensional numerical solutions of the Navier-Stokes Equations (NSE) are carried out alongside SWE solutions for nearly identical physical initial-value problems. Analysis of the solutions to the initial-value problem shows that the tendency to form either the lee-side height/velocity discontinuity in the SWE, or the overturning density interface in the NSE, is a feature of inviscid, nonturbulent fluid dynamics. Dissipative turbulent processes associated with the lee-side hydraulic jump are a consequence of the inviscid fluid dynamics that initiate and maintain the locally unstable conditions. Implications for the modeling of atmospheric mountain waves and lee vortices are discussed.

Refreshments:  3:15 PM

First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, November 9, 2017 - 3:30pm to 4:30pm

Piotr SmolarkiewiczEuropean Center for Medium Range Weather Forecasts (ECMWF)United Kingdom 

The talk highlights the development of the Finite-Volume Module (FVM) of the Integrated Forecasting System (IFS) at ECMWF. FVM represents an alternative dynamical core that enhances the spectral dynamical core of the IFS with new capabilities, such as a compact-stencil finite-volume discretisation, flexible meshes, conservative non-oscillatory PDATA transport, and all-scale nonhydrostatic governing equations. As a default, FVM solves the compressible Euler equations in a geospherical framework, using a centred two-time-level time-stepping scheme with 3D implicit treatment of acoustic, buoyant and rotational modes. A hybrid computational mesh, fully unstructured in the horizontal and structured in the vertical, enables efficient global atmospheric modelling. Theoretical considerations are illustrated with results of benchmark simulations of intermediate complexity, and comparison to the operational spectral dynamical core of the IFS.

Refreshments: 3:15 PM

Building:
Room Number: 
1022
Type of event:
Will this event be webcast to the public by NCAR|UCAR?: 
Calendar Timing: 
Friday, October 27, 2017 - 3:30am to 4:30am

Piotr Smolarkiewicz
European Center for Medium Range Weather Forecasts (ECMWF)
United Kingdom 

The talk highlights the development of the Finite-Volume Module (FVM) of the Integrated Forecasting System (IFS) at ECMWF. FVM represents an alternative dynamical core that enhances the spectral dynamical core of the IFS with new capabilities, such as a compact-stencil finite-volume discretisation, flexible meshes, conservative non-oscillatory PDATA transport, and all-scale nonhydrostatic governing equations. As a default, FVM solves the compressible Euler equations in a geospherical framework, using a centred two-time-level time-stepping scheme with 3D implicit treatment of acoustic, buoyant and rotational modes. A hybrid computational mesh, fully unstructured in the horizontal and structured in the vertical, enables efficient global atmospheric modelling. Theoretical considerations are illustrated with results of benchmark simulations of intermediate complexity, and comparison to the operational spectral dynamical core of the IFS.

Refreshments: 3:15 PM

First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, October 26, 2017 - 3:30pm to 4:30pm

Paul Field UK Met OfficeExeter, United Kingdom

We use convection permitting global aquaplanet simulations to explore the interaction between aerosol and mid-latitude cyclones. Based on model simulations we propose a hypothesis about how midlatitude cyclones will respond to increases in aerosol loading.  In this talk, I will introduce the model results and describe how we tested it with a decade of satellite observations and a more focused period coinciding with the Icelandic volcanic eruption in 2014.

Refreshments: 3:15 PM

Building:
Room Number: 
1022
Type of event:
Will this event be webcast to the public by NCAR|UCAR?: 
Calendar Timing: 
Friday, September 29, 2017 - 3:30am to 4:30am

Paul Field
UK Met Office
Exeter, United Kingdom

We use convection permitting global aquaplanet simulations to explore the interaction between aerosol and mid-latitude cyclones. Based on model simulations we propose a hypothesis about how midlatitude cyclones will respond to increases in aerosol loading.  In this talk, I will introduce the model results and describe how we tested it with a decade of satellite observations and a more focused period coinciding with the Icelandic volcanic eruption in 2014.

Refreshments: 3:15 PM

First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1022
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, September 28, 2017 - 3:30pm to 4:30pm

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