Events (Upcoming & Past)

Past MMM Events

Lotte BierdelLudwig Maximilians University Munich, Germany 

The current literature discussing predictability of atmospheric flow and the nature of the underlying scale interactions considers the problem from two main perspectives. One approach is based on statistical closure models in a homogeneous and isotropic turbulent flow, where the predictability time is determined solely by the background kinetic energy spectrum and not by the underlying dynamical model. An alternative approach is based on results from numerical weather prediction models that suggest that latent heat release associated with deep moist convection is a primary mechanism for small-scale error growth. From this point of view error growth in the atmosphere is an initially localized, highly intermittent phenomenon that expands upscale, leading to a complete loss of predictability on scales below 100 km within a few hours. The error growth process then depends on the underlying dynamics of the respective scale range and the errors in particular have to transition from geostrophically unbalanced to balanced motion while propagating through the mesoscale. In this talk a study will be presented that examines the geostrophic adjustment process as possibly underlying this transition. To that end, an analytical framework for the geostrophic adjustment of an initial pointlike pulse of heat (modeling a convective cloud or an error within the prediction of a cloud) is developed. Spatial and temporal scales of the geostrophic adjustment mechanism are deduced and three characteristics of the solution are shown to be potentially useful for identifying the geostrophic adjustment process in numerical simulations. These three predictions are then tested in the framework of error growth experiments in idealized numerical simulations of a convective cloud field. Three different rotation rates are employed in order to identify the geostrophic adjustment mechanism and allow a quantitative comparison with the predictions of the analytical model. As will be shown, the numerical simulations agree well with the predictions developed from the analytical model. Based on these findings it is suggested that the geostrophic adjustment process governs upscale error growth through the atmospheric mesoscales.

Refreshments: 3:15 PM

Building:
Room Number: 
1001 (Note Location)
Type of event:
Will this event be webcast to the public by NCAR|UCAR?: 
Calendar Timing: 
Friday, July 21, 2017 - 3:30am to 4:30am

Lotte Bierdel
Ludwig Maximilians University
Munich, Germany 

The current literature discussing predictability of atmospheric flow and the nature of the underlying scale interactions considers the problem from two main perspectives. One approach is based on statistical closure models in a homogeneous and isotropic turbulent flow, where the predictability time is determined solely by the background kinetic energy spectrum and not by the underlying dynamical model. An alternative approach is based on results from numerical weather prediction models that suggest that latent heat release associated with deep moist convection is a primary mechanism for small-scale error growth. From this point of view error growth in the atmosphere is an initially localized, highly intermittent phenomenon that expands upscale, leading to a complete loss of predictability on scales below 100 km within a few hours. The error growth process then depends on the underlying dynamics of the respective scale range and the errors in particular have to transition from geostrophically unbalanced to balanced motion while propagating through the mesoscale. In this talk a study will be presented that examines the geostrophic adjustment process as possibly underlying this transition. To that end, an analytical framework for the geostrophic adjustment of an initial pointlike pulse of heat (modeling a convective cloud or an error within the prediction of a cloud) is developed. Spatial and temporal scales of the geostrophic adjustment mechanism are deduced and three characteristics of the solution are shown to be potentially useful for identifying the geostrophic adjustment process in numerical simulations. These three predictions are then tested in the framework of error growth experiments in idealized numerical simulations of a convective cloud field. Three different rotation rates are employed in order to identify the geostrophic adjustment mechanism and allow a quantitative comparison with the predictions of the analytical model. As will be shown, the numerical simulations agree well with the predictions developed from the analytical model. Based on these findings it is suggested that the geostrophic adjustment process governs upscale error growth through the atmospheric mesoscales.

Refreshments: 3:15 PM

First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1001 (Note Location)
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, July 20, 2017 - 3:30pm to 4:30pm

Stipo SenticNew Mexico Tech

Tropical convective organization is the process in which disorganized convection organizes into regions of intense convective activity surrounded by dry, convectively inactive regions. Well known examples are tropical cyclones and the Madden-Julian Oscillation (MJO)—they affect atmospheric energetics, and the MJO affects virtually all weather on our planet. Recent advances in idealized modelling of tropical convection, namely the weak temperature gradient (WTG) approximation, enable us to study convective organization in idealized settings. The WTG approximation parameterizes the effects of the large-scale on local convection, and can be used in idealized sensitivity studies of convection to changes in large-scale convective environment. To model organized convection in the context of the MJO, we used observations from the Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign to force WTG simulations in a cloud resolving model, and test how well the WTG approximation reproduces variations in convective diagnostics: precipitation rate, stability, moisture content, and large-scale transport (gross moist stability). We find that the WTG approximation reproduces variations in these diagnostics, and relationships between them.  The ability of WTG approximation to reproduce important observed diagnostics provides confidence that this is a good strategy for exploring tropical phenomena.  An example that I'll talk about is the behavior of convective organization at different SSTs.

(Special Date) Tuesday, 30 May 2017, 3:30 PMRefreshments: 3:15 PM NCAR-Foothills Laboratory 3450 Mitchell LaneBldg. 2, Small Seminar Room 1001 (Note Location)

Building:
Room Number: 
1001 (Please note location)
Type of event:
Will this event be webcast to the public by NCAR|UCAR?: 
Calendar Timing: 
Wednesday, May 31, 2017 - 3:30am to 4:30am

Stipo Sentic
New Mexico Tech

Tropical convective organization is the process in which disorganized convection organizes into regions of intense convective activity surrounded by dry, convectively inactive regions. Well known examples are tropical cyclones and the Madden-Julian Oscillation (MJO)—they affect atmospheric energetics, and the MJO affects virtually all weather on our planet. Recent advances in idealized modelling of tropical convection, namely the weak temperature gradient (WTG) approximation, enable us to study convective organization in idealized settings. The WTG approximation parameterizes the effects of the large-scale on local convection, and can be used in idealized sensitivity studies of convection to changes in large-scale convective environment. To model organized convection in the context of the MJO, we used observations from the Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign to force WTG simulations in a cloud resolving model, and test how well the WTG approximation reproduces variations in convective diagnostics: precipitation rate, stability, moisture content, and large-scale transport (gross moist stability). We find that the WTG approximation reproduces variations in these diagnostics, and relationships between them.  The ability of WTG approximation to reproduce important observed diagnostics provides confidence that this is a good strategy for exploring tropical phenomena.  An example that I'll talk about is the behavior of convective organization at different SSTs.

(Special Date) Tuesday, 30 May 2017, 3:30 PM
Refreshments: 3:15 PM 
NCAR-Foothills Laboratory 
3450 Mitchell Lane
Bldg. 2, Small Seminar Room 1001 (Note Location)


First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1001 (Please note location)
Host lab/program/group:
Type of event:
Calendar Timing: 
Tuesday, May 30, 2017 - 3:30pm to 4:30pm

Michael TjernströmDepartment of Meteorology & Bolin Centre for Climate ResearchStockholm University, Sweden

Arctic climate is ultimately determined by a balance between meridional heat transport into the area, and radiation heat loss at the top of the atmosphere over the same area. Since the net radiation loss is due to small-scale processes parameterized in models, and the meridional heat flux is due to larger scale atmospheric dynamics resolved by the models, the two has usually been studied separately. In this seminar this concept will be called into question.

In an episode during the Arctic Clouds in Summer Experiment (ACSE) in the summer of 2014, warm air from the Siberian mainland flowed in over melting sea-ice in the East-Siberian Sea for over a week. As the ~25 °C warm air flowed over the melting surface, maintained at the melting point, a strong surface inversion formed in which dense fog also formed. This resulted in a positive net longwave radiation while the sensible heat flux was downward. Although solar radiation was attenuated by the fog, this led to an additional 10-20 Wm-2 energy to the surface. This led us to hypothesize a zone from the ice edge where the surface will receive enhanced energy when the atmospheric flow is northward onto the ice. 

To test this hypothesis, we analyzed the observation from the entire ACSE expedition. All temperature profiles taken over sea ice were categorized into cases with or without a surface inversion; the inversion cases where further divided into two categories using the humidity profiles. When projecting other observations onto these three classes, many are systematically different. Surface inversion with increasing moisture with height systematically added 10-20 Wm-2 energy to the surface energy budget, indicating that meridional heat flux must be considered together with the small-scale processes caused by the air mass transformation.

Please note the location change.

Thursday, 1 June 2017, 3:30 PMRefreshments:  3:15 PM NCAR-Foothills Laboratory3450 Mitchell Lane Bldg. 2, Small Seminar Room 1001 

Building:
Room Number: 
1001 (Please note location change)
Type of event:
Will this event be webcast to the public by NCAR|UCAR?: 
Calendar Timing: 
Friday, June 2, 2017 - 3:30am to 4:30am

Michael Tjernström
Department of Meteorology & Bolin Centre for Climate Research
Stockholm University, Sweden

Arctic climate is ultimately determined by a balance between meridional heat transport into the area, and radiation heat loss at the top of the atmosphere over the same area. Since the net radiation loss is due to small-scale processes parameterized in models, and the meridional heat flux is due to larger scale atmospheric dynamics resolved by the models, the two has usually been studied separately. In this seminar this concept will be called into question.

In an episode during the Arctic Clouds in Summer Experiment (ACSE) in the summer of 2014, warm air from the Siberian mainland flowed in over melting sea-ice in the East-Siberian Sea for over a week. As the ~25 °C warm air flowed over the melting surface, maintained at the melting point, a strong surface inversion formed in which dense fog also formed. This resulted in a positive net longwave radiation while the sensible heat flux was downward. Although solar radiation was attenuated by the fog, this led to an additional 10-20 Wm-2 energy to the surface. This led us to hypothesize a zone from the ice edge where the surface will receive enhanced energy when the atmospheric flow is northward onto the ice. 

To test this hypothesis, we analyzed the observation from the entire ACSE expedition. All temperature profiles taken over sea ice were categorized into cases with or without a surface inversion; the inversion cases where further divided into two categories using the humidity profiles. When projecting other observations onto these three classes, many are systematically different. Surface inversion with increasing moisture with height systematically added 10-20 Wm-2 energy to the surface energy budget, indicating that meridional heat flux must be considered together with the small-scale processes caused by the air mass transformation.

Please note the location change.

Thursday, 1 June 2017, 3:30 PM
Refreshments:  3:15 PM
NCAR-Foothills Laboratory
3450 Mitchell Lane
Bldg. 2, Small Seminar Room 1001 

First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1001 (Please note location change)
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, June 1, 2017 - 3:30pm to 4:30pm

Sharon SessionsDepartment of Physics, New Mexico TechSocorro, New Mexico

Tropical convection is difficult to understand and even more difficult to predict, in part because of the interplay between the convection itself and the large scale circulations.  Predictability is possible, however, if the  scales of convective disturbances are large enough that they are influenced by voriticity anomalies in the environment.  Ooyama, in 1982, discussed this idea in the context of mature tropical cyclones, in a process he refered to as "cooperative intensification".  Recently, Raymond et al. (2015) revisted Ooyama's ideas and addressed the question of whether other less extreme types of tropical disturbances could be a response to a nonlinear form of "balanced dynamics".  If so, they argued that these types of disturbances would have potential for predictability (and therefore would also be parameterizable).  In terms of time scales, disturbances which occur on scales longer than the time to establish balance, are candidates for predictability based on the potential for moist convection to evolve as a balanced response to large scale vorticity anomalies.  

In this talk, I'll revisit some of Ooyama's and Raymond's ideas regarding balance dynamics, and discuss how we would look for signatures of balanced dynamics in convective systems.  I'll also discuss the mechanism by which a vorticity anomaly can modulate and strengthen a developing convective system, and address the question of whether the Madden-Julian Oscillation is a candidate for a convective disturbance under the influence of balanced dynamics.  Finally, I discuss how these concepts can potentially be used to evaluate and diagnose global models that have varying degrees of skill in simulating tropical disturbances (and the MJO in particular).  

Special Wednesday Date--Rescheduled from 18 May 2017 Due to Weather

Wednesday, 24 May 2017, 3:30 PMRefreshments 3:15 PM NCAR--Foothills Laboratory 3450 Mitchell Lane Bldg. 2, Main Auditorium, Room 1022 

 

 

Building:
Room Number: 
1022
Type of event:
Will this event be webcast to the public by NCAR|UCAR?: 
Calendar Timing: 
Thursday, May 25, 2017 - 3:30am to 4:30am

Sharon Sessions
Department of Physics, New Mexico Tech
Socorro, New Mexico

Tropical convection is difficult to understand and even more difficult to predict, in part because of the interplay between the convection itself and the large scale circulations.  Predictability is possible, however, if the  scales of convective disturbances are large enough that they are influenced by voriticity anomalies in the environment.  Ooyama, in 1982, discussed this idea in the context of mature tropical cyclones, in a process he refered to as "cooperative intensification".  Recently, Raymond et al. (2015) revisted Ooyama's ideas and addressed the question of whether other less extreme types of tropical disturbances could be a response to a nonlinear form of "balanced dynamics".  If so, they argued that these types of disturbances would have potential for predictability (and therefore would also be parameterizable).  In terms of time scales, disturbances which occur on scales longer than the time to establish balance, are candidates for predictability based on the potential for moist convection to evolve as a balanced response to large scale vorticity anomalies.  

In this talk, I'll revisit some of Ooyama's and Raymond's ideas regarding balance dynamics, and discuss how we would look for signatures of balanced dynamics in convective systems.  I'll also discuss the mechanism by which a vorticity anomaly can modulate and strengthen a developing convective system, and address the question of whether the Madden-Julian Oscillation is a candidate for a convective disturbance under the influence of balanced dynamics.  Finally, I discuss how these concepts can potentially be used to evaluate and diagnose global models that have varying degrees of skill in simulating tropical disturbances (and the MJO in particular).  

Special Wednesday Date--Rescheduled from 18 May 2017 Due to Weather

Wednesday, 24 May 2017, 3:30 PM
Refreshments 3:15 PM
NCAR--Foothills Laboratory
3450 Mitchell Lane
Bldg. 2, Main Auditorium, Room 1022 

 

 

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: 
Wednesday, May 24, 2017 - 3:30pm to 4:30pm

Anders SivleNorwegian Meteorological InstituteOslo, Norway 

Different people in different occupations depend on weather forecasts to plan their work and recreational schedules. People with no expertise in meteorology frequently interpret weather forecasts and uncertainty information. These non-experts apply their prior knowledge and experiences in a variety of fields to synthesize different types of information to interpret forecasts. In this PhD study, situations of typical users were simulated when examining how different user groups interpret, integrate, and use information from an online weather report (www.Yr.no) in their everyday decision-making. First, qualitative interviews of twenty-one Norwegians (farmers, exterior painters, tour guides, teachers and students) were conducted. Second, sixteen students participated in an eye-tracking study.

The study found that nuances such as color and the number of drops were important in the interpretations of the weather symbols and forecast uncertainty, which were sometimes interpreted differently than intended by the forecast provider. Prior knowledge and the integration of information from different representations affected the participants’ interpretations. The decision-making process influenced the selections of representations in different situations; their selection was dependent on the importance of the envisaged activity and the weather conditions for the day. Additionally, in situations in which the participants had a lack of experiences, this lack provides a possible explanation for why part of the information was occasionally not understood and used.

Some implications of the findings for communication and future research will be discussed in the presentation. For example, it appears that some users should be supported to facilitate the interpretation and use of information in situations where they lack experiences. One possibility to support persons that lack experiences and have low situation awareness might be to provide consequences and impacts of forecast weather. 

Thursday, 8 June 2017, 3:30 PM Refreshments 3:15 PM NCAR-Foothills Laboratory 3450 Mitchell Lane (Location Change) Bldg. 2, Room 1001

Building:
Room Number: 
1001 (Please note location change)
Type of event:
Will this event be webcast to the public by NCAR|UCAR?: 
Calendar Timing: 
Friday, June 9, 2017 - 3:30am to 4:30am

Anders Sivle
Norwegian Meteorological Institute
Oslo, Norway 

Different people in different occupations depend on weather forecasts to plan their work and recreational schedules. People with no expertise in meteorology frequently interpret weather forecasts and uncertainty information. These non-experts apply their prior knowledge and experiences in a variety of fields to synthesize different types of information to interpret forecasts. In this PhD study, situations of typical users were simulated when examining how different user groups interpret, integrate, and use information from an online weather report (www.Yr.no) in their everyday decision-making. First, qualitative interviews of twenty-one Norwegians (farmers, exterior painters, tour guides, teachers and students) were conducted. Second, sixteen students participated in an eye-tracking study.

The study found that nuances such as color and the number of drops were important in the interpretations of the weather symbols and forecast uncertainty, which were sometimes interpreted differently than intended by the forecast provider. Prior knowledge and the integration of information from different representations affected the participants’ interpretations. The decision-making process influenced the selections of representations in different situations; their selection was dependent on the importance of the envisaged activity and the weather conditions for the day. Additionally, in situations in which the participants had a lack of experiences, this lack provides a possible explanation for why part of the information was occasionally not understood and used.

Some implications of the findings for communication and future research will be discussed in the presentation. For example, it appears that some users should be supported to facilitate the interpretation and use of information in situations where they lack experiences. One possibility to support persons that lack experiences and have low situation awareness might be to provide consequences and impacts of forecast weather. 

Thursday, 8 June 2017, 3:30 PM
Refreshments 3:15 PM
NCAR-Foothills Laboratory
3450 Mitchell Lane
(Location Change) Bldg. 2, Room 1001

First Name: 
Bobbie
Last Name: 
Weaver
Phone Extension (4 digits): 
8946
Email: 
weaver@ucar.edu
Building:
Room Number: 
1001 (Please note location change)
Host lab/program/group:
Type of event:
Calendar Timing: 
Thursday, June 8, 2017 - 3:30pm to 4:30pm

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