Staff Notes Daily Calendar Events

Friday, December 5, 2014 - 10:30am

Chiel C. van Heerwaarden
Max Planck Institute for Meteorology
Hamburg, Germany


The heterogeneously heated free Convective Boundary Layer (CBL) is investigated by means of dimensional analysis and results from Large-Eddy Simulations (LES) and Direct Numerical Simulations (DNS).The investigated physical model is a CBL that forms in a linearly stratified atmosphere heated from the surface. We present results from two different experiments: a CBL that is heated from patches with afixed surface heat flux, and a CBL that is heated from stripes with a fixed surface temperature.

For the first experiment, we show that each simulation, if run long enough, contains first the formation of a peak in kinetic energy, corresponding to the “optimal” heterogeneity size with strong secondary circulations, and subsequently the transition into a horizontally homogeneous CBL. We have developed scaling laws for the time of the optimal state and transition that show that the optimal state and transition do not occur at a fixed ratio of the heterogeneity size to the CBL thickness. Instead, these occur at a higher ratio for simulations with increasing heterogeneity sizes, due to the development of structures in the downward moving air that grow faster than the CBL thickness.

For the second experiment, we show that imposing a fixed surface temperature changes the physics dramatically. In contrast to the first experiment, the system develops towards a steady state where the release of heat from the warm stripes equals the amount of heat taken up from the cold stripes. In this development, the system can go into transition to a horizontally homogeneous CBL and subsequently change back to a state with strong secondary circulations. Furthermore, large stripe sizes lead to oscillations in the kinetic energy and asymmetry in the plume circulations.

This seminar will be webcast live at:
http://www.fin.ucar.edu/it/mms/fl2-live.htm

Recorded seminar link can be viewed here:
https://www.mmm.ucar.edu/events/seminars

***Please join us on this special day and time for our MMM seminar***
Friday, 5 December 2014, 10:30 AM
Refreshments 10:15 AM
NCAR-Foothills Laboratory
3450 Mitchell Lane
Bldg 2 Small Seminar Room 1001

Presenter(s):
Chiel C. van Heerwaarden
Type of event:
Seminar/Symposium
Building:
FL2
Room:
1001

Posted by MIchelle Menard (menard@ucar.edu) at x8189
Lab/division hosting the event:
NCAR, NESL, MMM
Affiliation or organization:
Wednesday, December 10, 2014 - 11:00am

Abstract: Clouds are not only fascinating to watch for their myriad of shapes, but are also scientifically challenging because their formation requires both knowledge about the large-scale meteorological environment as well as knowledge about the details of cloud droplet and ice crystal formation on the micro-scale. The ice phase in cloud remains enigmatic because ice crystal number concentrations can exceed the number concentrations of those aerosol particles acting as centers for ice crystals (so-called ice nuclei) by orders of magnitude. To date, measurement devices for ice nuclei are rare and custom-made. In this work, I present the significant progress that has been made in the ice nucleation community in identifying which aerosol particles may act as ice nuclei and why.

As pointed out in the fifth assessment report of the Intergovernmental Panel on Climate Change, the radiative forcing due to aerosol-cloud interactions remains the largest uncertainty of the anthropogenic forcings. On the other hand, how clouds change in a warmer climate is the largest of uncertainties in terms of the expected warming at a point of doubling of carbon dioxide.

Presenter(s):
Prof. Ulrike Lohmann
Type of event:
Seminar/Symposium
Building:
Mesa Lab
Room:
Main Seminar Room

Posted by Scott Briggs (sbriggs@ucar.edu) at x1607
Lab/division hosting the event:
NCAR, ASP
Thursday, December 11, 2014 - 11:00am

Abstract: Aerosol-cloud interactions constitute the highest uncertainties in radiation forcing estimates. Uncertainties due to the phase and longevity of mixed-phase clouds (MPCs) influence the radiative balance and the hydrological cycle. Due to Wegener-Bergeron-Findeisen-process (WBF) which describes the glaciation of MPC due to the lower saturation vapor pressure over ice than over water, the MPCs are mostly expected to be short-lived. In contrast, in-situ measurements have shown that MPCs can persist over longer time.

We present measurements obtained at the high-altitude research station Jungfraujoch (JFJ, 3580 m asl) in the Swiss Alps partly taken during the CLoud-Aerosol Interaction Experiments (CLACE). During the winter season, the JFJ has a high frequency of super-cooled clouds and is considered representative for being in the free troposphere. In-situ measurements of the microstructure of MPCs have been obtained with the digital imager HOLIMO II, that delivers phase-resolved size distributions, concentrations, and water contents. The data set of MPCs at JFJ shows that for northerly wind cases partially-glaciated MPCs are more frequently observed than for southerly wind cases. The higher frequency of these intermediate states of MPCs at the JFJ suggests either higher updraft velocities, and therefore higher supersaturations with respect to water, or the absence of sufficiently high IN concentrations to quickly glaciate the MPC.

Because of the limitation of the in-situ information, i.e. point measurements and missing measurements of vertical velocities at JFJ, the mechanism of the long persistence of MPCs at JFJ cannot be fully understood. Therefore, in addition to measurements we investigate the JFJ region with a regional model study with a new version of the non-hydrostatic model COSMO that includes the online coupled Aerosol reactive trace gases model (ART) and the aerosol module M7. The combination of kilometer-scale simulations with measurements allows to systematically study the effect of vertical velocity and temperatures on MPCs at JFJ, the synoptic conditions, origins of air masses and aerosol concentration.

Presenter(s):
Prof. Ulrike Lohmann
Type of event:
Seminar/Symposium
Building:
FL2
Room:
Large Auditorium (1022)

Posted by Scott Briggs (sbriggs@ucar.edu) at x1607
Lab/division hosting the event:
NCAR, ASP
Tuesday, December 2, 2014 - 3:30am

Plains elevated convection at night: the PECAN project

The PECAN campaign (June-July 2015) is a multi-agency project (NSF, NOAA, NASA, DOE) designed to advance the understanding of continental, nocturnal, warm-season precipitation. PECAN will focus on nocturnal convection in conditions over the central Great Plains with a stable boundary layer (SBL), a low-level jet (LLJ) and the largest CAPE located above the SBL. Thunderstorms are most common after sunset across this region in summer, and much of the resulting precipitation falls from MCSs. To date, an accurate prediction and an in-depth understanding of elevated convection in this environment remains an elusive goal. While the initiation of deep convection (CI) in well-mixed daytime boundary layers occurs along pre-existing boundaries of surface convergence, the initiation of nocturnal convection above the SBL is poorly understood and relatively unexplored. Nocturnal CI and MCS maintenance may be controlled by vertical parcel displacements due to undular bores and non-linear wave-like features triggered by the MCS cold pools. It remains uncertain how the dynamics and microphysics of MCSs evolve as the boundary layer stabilizes in response to nocturnal radiative cooling, and what controls the decoupling of strong winds from the surface. Finally, PECAN aims to improve NWP, in particular nocturnal QPF in the Great Plains, mainly by means of a mesoscale network of thermodynamic and kinematic profiling systems.

Tuesday, 2 December 2014, 3:30PM
NCAR-Foothills Laboratory
3450 Mitchell Lane
Bldg. 2 Large Auditorium (Rm 1022)
Webcast Link: http://www.fin.ucar.edu/it/mms/fl-live.htm

Presenter(s):
Bart Geerts
Type of event:
Seminar/Symposium
Building:
FL2
Room:
1022 (Large Auditorium)

Posted by Whitney Robinson (wrobs@ucar.edu) at x8713
Lab/division hosting the event:
NCAR, EOL
Affiliation or organization:
Wednesday, December 10, 2014 - 12:15pm

Since their introduction in 1990, regional climate models (RCMs) have been widely used to study the impact of climate change on human health, ecology, and epidemiology. To ensure that the conclusions of impact studies are well founded, it is necessary to assess the uncertainty in RCMs. This is not an easy task since two major sources of uncertainties can undermine an RCM: uncertainty in the boundary conditions needed to initialize the model and uncertainty in the model itself.  

In this paper we present a statistical modeling framework to assess an RCM driven by analyses. More specifically, our scientific interest here is determining whether there exist time periods during which the RCM in consideration displays the same type of spatial discrepancies from the observations. The proposed model can be seen as an exploratory tool for atmospheric modelers to identify time periods that require a further in depth examination. Focusing on seasonal average temperature and seasonal maximum temperature, our model relates the corresponding observed seasonal fields to the RCM output via a hierarchical Bayesian statistical model that includes a spatio-temporal calibration term. The latter, which represents the spatial error of the RCM, is in turn provided with a Dirichlet process prior, enabling clustering of the errors in time. 
 
On the first level of the hierarchy, the model specifies a normal distribution for seasonal average temperature and a continuous GEV spatial process for seasonal maximum temperature. We apply our modeling framework to data from Southern Sweden spanning the period December 1, 1962 to November 30, 2007. Our analysis reveals intriguing tendencies with respect to the RCM spatial errors relative to seasonal average temperature; on the other hand, no systematic spatial error is detected for seasonal maximum temperature during the period 1963-2007.  
Presenter(s):
Veronica Berrocal
Type of event:
Seminar/Symposium
Building:
Mesa Lab
Room:
Chapman Room

Posted by Carolyn Mueller (cmueller@ucar.edu) at x2491
Lab/division hosting the event:
NCAR, CISL, IMAGe
Affiliation or organization:
Tuesday, December 2, 2014 - 2:00pm

IPCC Chapter 13: Sea Level Change

Ever wonder what the Intergovernmental Panel on Climate Change (IPCC) report says?  Learn more Tuesday and Thursday afternoons this fall during a seminar series by IPCC authors and contributors. This fall’s focus is on Climate Change 2013: The Physical Science Basis (Working Group I’s contribution to the IPCC 5th Assessment Report).

Presenter(s):
Steve Nerem
Type of event:
Seminar/Symposium
Building:
CIRES Auditorium at CU-Boulder

Posted by Gaylynn Potemkin (potemkin@ucar.edu) at x1618
Lab/division hosting the event:
External:, CIRES-ATOC
Tuesday, December 9, 2014 - 2:00pm

IPCC Chapter 14: Climate Phenomena and their Relevance for Future Regional Climate Change

Ever wonder what the Intergovernmental Panel on Climate Change (IPCC) report says?  Learn more Tuesday and Thursday afternoons this fall during a seminar series by IPCC authors and contributors. This fall’s focus is on Climate Change 2013: The Physical Science Basis (Working Group I’s contribution to the IPCC 5th Assessment Report).

Presenter(s):
Kevin Trenberth
Type of event:
Seminar/Symposium
Building:
CIRES Auditorium at CU-Boulder

Posted by Gaylynn Potemkin (potemkin@ucar.edu) at x1618
Lab/division hosting the event:
External:, CIRES-ATOC
Affiliation or organization:
Thursday, December 4, 2014 - 3:30pm

Juan-Pedro Mellado
Max Planck Institute for Meteorology
Hamburg, Germany

This seminar presents new insights into small-scale turbulent mixing at the boundary-layer top gained using direct numerical simulations. First we show that, under cloud-free conditions, the entrainment zone is better characterized by two length-scales rather than one. This duplicity of scales explains the observed dependence of entrainment-zone properties on weak- and strong tropospheric stratification regimes. Second, for the stratocumulus-topped boundary layer, we demonstrate that mixing enhancement by wind shear can render evaporative cooling as important as other sources of turbulence at the cloud top. This result implies that, even though its effect is indirect, wind shear must be taken into account for a correct representation of entrainment at the cloud top.


This seminar will be webcast live at:
http://www.fin.ucar.edu/it/mms/fl-live.htm

Recorded seminar link can be viewed here:
https://www.mmm.ucar.edu/events/seminars

Thursday 4, December 2014, 3:30 PM
Refreshments 3:15 PM
NCAR-Foothills Laboratory
3450 Mitchell Lane
Bldg 2 Small Seminar Room 1022

Presenter(s):
Juan-Pedro Mellado
Type of event:
Seminar/Symposium
Building:
FL2
Room:
1022

Posted by Michelle Menard (menard@ucar.edu) at x8189
Lab/division hosting the event:
NCAR, NESL, MMM
Affiliation or organization:
Tuesday, December 9, 2014 - 3:30pm
One of the most populated regions (Indo-Gangetic Plain) of the world is located in south Asia, where varieties of anthropogenic and biogenic emission sources are housing. On the other hand, pristine regions like the Himalayas and the oceanic regions are also located here and making this region an ideal laboratory to study influences of diverse emissions, dynamics and photochemistry. In view of this and realizing the scarcity of observational data, an observational facility was setup at ARIES, Nainital (29.4N, 79.5E; 1950 m) in the central Himalayas and at two sites in the IGP region. Surface observations of different trace gases (Ozone, CO, NO, NOy, light NMHCs, SO2, CO2 and other GHGs) and aerosols are initiated. Regular, once in a week, balloon-borne measurements of ozone, RH, temperature and GPS winds are also being made since January 2011. Observations at mountain site show signature of relative clean environment, while observations in IGP regions are strongly influenced by local and regional pollutions. A strong seasonal cycle in the lower tropospheric ozone with highest values during spring (~ 100 ppbv) and lowest during summer-monsoon (20-40 ppbv) is discerned. Few events of downward ozone transport are seen, but such influences are seen to be weaker in the eastern part of the Himalayas. Influences of biomass burning are seen even over the central Himalayas. In-contrast to trace gases over the central Himalayas, surface BC level is higher in winter and AOD and aerosol absorption are highest in spring over IGP. Further analysis of these observations with the help of air trajectories, satellite data and WRF-Chem model will be discussed.
Presenter(s):
Dr. Manish Naja
Type of event:
Seminar/Symposium
Building:
Foothills Labs
Room:
1022

Posted by Dianne Hodshon (dhodshon@ucar.edu) at x1401
Lab/division hosting the event:
NCAR, NESL, ACD
Affiliation or organization: