Brewer-Wilson Seminar Series Past Events 2016 /
18
Nov
2016
Thermohaline Instability and the Formation of North Atlantic Super Polynyas during the Glacial
Climate variability recorded in Greenland ice cores over the past 100,000 years is interspersed by a number of rapid warming events. Each warming event is approximately 10 to 15 degrees C in annual average temperature at summit Greenland. Each of these events in the climate record is also estimated to have occurred in less than a couple of decades. A modelling simulation of the glacial climate with a fully coupled climate model reveals that the initial warming event is triggered by thermohaline instability under a North Atlantic covered by sea ice. The initial instability is characterized by the formation of a wintertime glacial super polynya at the beginning of each warming event. Afterwards, the resumption of the Atlantic Meridional Overturning Circulation (AMOC) from a reduced state occurs within a couple of decades. I will describe some of the interesting physics underlying the instability.
04
Nov
2016
40 years of atmospheric methane FTIR observations from a remote European site
Observation of solar radiation in the infrared have been performed since the mid-fifties at the International Scientific Station of the Jungfraujoch (ISSJ, Swiss Alps, 46.5°N, 8.0°E, 3580 m a.s.l.), in the framework of the Network for Detection of Atmospheric Change (NDACC, www.ndacc.org<http://www.ndacc.org>). Systematic monitoring of the chemical composition of the Earth's atmosphere started in 1984 by using two state-of-the‐art Fourier Transform InfraRed (FTIR) instruments, while grating spectrometers were used previously in the early 1950s, and from the mid-1970s onwards, covering 40 years of quasi-continuous solar observations. In this framework, I will discuss optimization of retrieval strategies from infrared solar observations and methane trend analysis.
28
Oct
2016
Quantifying emissions of CO and NOx using observations from MOPITT, OMI, TES, and OSIRIS
We use the GEOS-Chem four-dimensional variational (4D-var) data assimilation with satellite observations of multiple chemical species to estimate emissions of CO and NOx, as well as the tropospheric concentrations of O3. In doing so, we utilize CO retrievals from The Measurements of Pollution In The Troposphere (MOPITT), O3 retrievals from the Tropospheric Emission Spectrometer (TES), O3 retrievals from the Optical Spectrograph and InfraRed Imager System (OSIRIS), and NO2 columns from the Ozone Monitoring Instrument (OMI). By integrating these data in the 4D-Var scheme, we obtain a chemical state in the model that is consistent with all of the data over the assimilation period. In this context, for example, we find that combining TES and OSIRIS improves O3, particularly in the tropical upper troposphere (by 10-20%), which leads to a reduction in the uncertainty of the NOx emission estimates. However, although assimilating multiple chemical species provides a stronger constraint on the chemical, state, there are still large uncertainties on the CO and NOx emission estimates, due to the dependence of the results on the selection of the assimilation window and how the datasets are weighted in the cost function.
14
Oct
2016
Polar Low Induced Surface Ozone and HDO Depletion
Ground-based and satellite datasets were used to identify two similar polar low induced surface ozone depletion events in Eureka, Canada on March 2007 and April 2011. These two events coincident with observations of depleted HDO, indicate the condensation process during the transportation of the ozone depleted airmass. Lidar and radar measured the ice clouds and aerosol when the ozone and HDO depleted airmass arrived in Eureka. Two global chemical-climate models were used to simulate the surface ozone depletion. A global reanalysis model data and a particle dispersion model were used in this work to study the link between the ozone and HDO depletion. Observational and modelled data show these events have the distinctive feature of coincident of the strong tropospheric cyclone and intensified stratospheric vortex.
14
Oct
2016
Using space-based chlorophyll fluorescence and CO2 observations to constrain primary production and respiration about the boreal ecosystems
Sun-induced chlorophyll fluorescence (SIF), radiation emitted by vegetation during photosynthesis, has long been known to be a good proxy for primary productivity. However, only within the last few years have high-resolution space-based spectrometers allowed global observations of SIF. In this talk, I will examine how SIF observations from the GOME-2 satellite compare with primary productivity estimates from terrestrial ecosystem models. I will then introduce a method to combine space-based SIF observations with atmospheric CO2 observations to constrain both primary productivity and respiration in boreal terrestrial ecosystems.
07
Oct
2016
The atmospheric response to extratropical ocean warming induced by sea ice loss
Sea ice loss impacts the atmosphere by altering the surface energy balance, warming the Arctic lower troposphere, and potentially changing the large scale atmospheric circulation at mid-latitudes. A large number of studies have carried out numerical modeling experiments to isolate the atmospheric impacts of sea ice loss from other effects. These typically use an Atmospheric General Circulation Model (AGCM) forced with reduced sea ice concentrations while keeping sea surface temperatures and other forcings fixed. As the ocean cannot respond, these experiments ignore potentially important thermodynamic and dynamical feedbacks with the ocean. In this talk, I will examine the impact extratropical ocean warming caused by sea ice loss has on the atmosphere using both coupled ocean-atmosphere climate model and AGCM experiments. I will show that the extratropical ocean warming amplifies the atmospheric circulation response to sea ice loss, suggesting that previous studies using only AGCM experiments may underestimate the response.
07
Oct
2016
Why are upward EP-flux and temperature positively skewed in the stratosphere?
Polar stratospheric temperatures are positively skewed, with a typical value of skewness of 0.64 in Northern Hemisphere winter, an asymmetry that determines the character of ozone climate coupling and stratosphere-troposphere interactions. This skewness is often attributed to the fact that temperatures are bounded from below by a radiative limit while dynamical wave-driven events like sudden stratospheric warmings can cause significantly larger positive anomalies. In this talk, I will examine the positive skewness of upward wave activity flux itself as a driver of the temperature distribution. I will use the ideas of linear interference to explain the positive skewness of upward wave activity flux. In particular, I will show that a nonlinear relationship between the two terms that make up the heat flux anomaly can be used to explain its positive skewness. Finally, by using a toy statistical model of wave interference in the lower stratosphere, and I will show that the westward tilt of the climatological wave is the key ingredient to obtaining a positively skewed upward wave activity flux distribution.
30
Sep
2016
The mid-Pliocene CESM1 climatology
A very interesting time-period in the recent past is the mid-Pliocene (~3 Millions years ago). The configuration of the world looked much the same as today, CO2 was likely less than present day, but still the temperatures were much warmer and sea-level ~15-20m higher. If it is possible for the earth system to have such an extreme response to greenhouse gas concentrations no different from today’s, then it raises questions about the level of faith that can be put into climate model projections of only ~1 m of sea-level rise by the end of this century.
18
Mar
2016
NO2 Limb Retrieval in the Upper Troposphere/ Lower Stratosphere Region
26
Feb
2016
Reassessing the Ancient Martian Ocean Hypothesis using Global Distribution of Valley Networks
19
Feb
2016
Hybrid method: high-resolution imaging in lower mantle region
19
Feb
2016
A new characterization of the turbulent diapycnal diffusivities of mass and momentum in the ocean
05
Feb
2016
Detection of NH3 emissions in the Canadian Arctic from the 2014 Northwest Territories Fires
05
Feb
2016
Planetary surface mobility and the effect of core size, viscosity contrast and internal heating rate
29
Jan
2016
A How-to on Modifying CESM Conditions to Implement Interesting Experiments
22
Jan
2016
Quantifying CH4 emissions: from global to local scales