Mesoscale eddy fluxes play an important role in ocean transport. Coarse resolution climate models parameterize these fluxes in terms of diffusion coefficients, and improving such parameterizations remains an active topic of research. Recently, significant progress has been made in both describing and understanding the spatial variability in mesoscale diffusivity. The latter has mainly been in...
The global overturning of ocean waters involves the equatorward transport of cold, deep waters and the poleward transport of warm, near-surface waters. Such movement creates a net poleward transport of heat that, in partnership with the atmosphere, establishes the global and regional climates. Although oceanographers have long assumed that a reduction in deep water formation at high latitudes in the North Atlantic translates...
This week GS Yang Tian will lead the discussion on the attached paper titled ”weakening of the stratospheric polar vortex by Arctic sea-ice loss." Attached is also a related review paper by Cohen et al (2014).
Briefly: "In spite of mean global surface warming, an ostensibly large number of high-impact cold extremes have occurred in the Northern Hemisphere mid-latitude over the past decade. One hypothesis is that Arctic amplification, i.e. the greater warming of the Arctic compared with lower latitudes, alters the large scale circulation to states that favor extreme...
GS Jiahua Guo will be discussing Lewis and Karoly (2013) and Perkins et al. (2014), attached. She summarizes the discussion below:
The Australian ‘angry summer” of 2012/2013 was the warmest on record since1910. Such high temperatures are also coincident with bush fires and severe flooding. Before the summer, late onset of the Australian monsoon and below average rainfall primed the continent for extremely hot summer weather. This paper (Lewis and Karoly 2013) is trying to consider the possible anthropogenic contribution to extreme seasonal temperatures...
This week GS Alex Robel will discuss Roe & Baker (2014), and he summarizes the attached paper as the following:
There has been focus recently on the length changes of mountain glaciers around the world. In this week's ClimaTea, we will discuss work by Roe and colleagues exploring how glaciers integrate noise from the climate system, producing fluctuations in length. They make the basic observation that glaciers have memory, which responds to local temperature and precipitation through the glacier mass balance. This can be captured by models...
The seasonal variability of the polar stratospheric vortex is studied in a simplified AGCM driven by specified equilibrium temperature distributions. Seasonal variations in equilibrium temperature are imposed in the stratosphere only, enabling the study of stratosphere-troposphere coupling on seasonal timescales, without the...
GS Leah Birch will be presenting the attached two papers, and her summary is below:
Clouds have a two-fold effect in the atmosphere, as they promote both cooling and heating. Due to their size, they are often a great source of uncertainty in GCMs, so it is important to look at results critically. This week I will focus on the warming effect that clouds may have in the context of deglaciation from a Snowball Earth. We will discuss two papers by Abbot et. al. (2012) and Abbot (2014) in an effort to understand the heating ability of clouds and the limitations we think are present...
This week GS Chris Horvat is going to lead the discussion and explore how modern GCMs simulate sea ice, and two ways modelers have been led into traps while modeling it. First, Moon and Wettlaufer (2014) (attached) explore modeling of growth and decay in variable ice-cover regions in GCMs, showing that the when simple sea ice models were extended to these regions (which constitute a majority of the Arctic and Antarctic regions), the extension: (a) "violates the basic rules of calculus" (b) "neglects a leading order latent heat flux" and therefore (c) cannot capture the influence of the ice...
GS Karen McKinnon will be presenting Miralles et al. (2014), "Mega-heatwave temperatures due to combined soil desiccation and atmospheric heat accumulation."
Miralles and co-authors present case studies of the large heat waves in Europe in 2003 and Russia in 2010. Using both data (satellites, balloon measurements) and a land surface-atmosphere model, they examine the land surface and atmospheric conditions that allowed for the large heat waves. They find that mega-heatwaves require both the 'correct' synoptic conditions and a desiccated land surface -- and the locations of most...