Guest essay by Michael Wallace, Hydrologist and Graduate Student at UNM Dept of Nanoscience and Microsystems.
I am a hydroclimatologist who works and researches in the area of solar based climate forecasting. In advancing that, I’ve adapted data from various sources of my interest and have run that data through various graphical and stochastic exercises. This has sometimes led to improvements in my forecasting techniques, as well as interesting and apparently unique graphics. I am presenting some of this material next week at a conference focused on the Animas River in the Southern Rocky Mountains. I also post on much of this material at my non-interactive blog at http://www.abeqas.com.
An internet search on “geostrophic winds” can set the background for this post. In my examples and likely those of others, these winds are averaged across the “entire” atmosphere (100 km according to many sources) and then mapped across the globe. The patterns can be both useful and intriguing. While most other researchers (both orthodox and skeptic alike) appear to favor one or several particular layer(s) of the atmosphere, I favor the full atmosphere for much of my climate work. Accordingly this post is about some examples of those full atmosphere based patterns. Much of my work is still on a steep learning curve across a number of fronts so my apologies in advance as I stumble through topics where my knowledge is still sketchy. I hope readers will view this post as simply an informal report of some work in progress and of course comments are welcome.
It seems safe to suggest that averages of the full atmosphere contoured over any region including and up to the full globe, are an intrinsic adoption of quasi-geostrophic theory (QG). I am still combing through the rich details that the QG perspective affords, precisely because of its useful and often overlooked simplifications. These limitations are somewhat similar to the ones I’ve long worked in as a hydrogeologic modeler of energy and mass transport in porous media within multiphase flow conditions.
QG approaches are quasi-three dimensional and they can violate many more fully 3D principles at sub synoptic scales (synoptic scale is 1,000 kilometer (km)). For example, QG can nominally fail at some scales in the presence of other larger scale baroclinic and/or vertically sheared domains which are well known. Yet the QG simplifications have proven useful, even in many of those very environments, especially for forecasting moisture frontal movements associated with high velocity parcels moving within the jet streams.
QG theory based forecasts of storms that form in response to bends and velocity changes within jet streams are already well established. Moreover, they are widely agreed to work very well. The QG methods employ a curious conceptualization of a limited segment of relatively high velocity flow within a jet stream. Vortices exist in each corner. The directions of convection and subsidence vary with each corner vortex in relation to the direction of flow within the jet stream segment. All is explained well, by many sources, via reference to so called geostrophic flows which are linked to the Coriolis effect and thermal gradients. There are indeed challenging and dynamic 3D components to the actual systems as well, and notably some aspects of the circulations are often described in terms of the “atmospheric conveyor belt”. Even so, the QG simplifications work at the synoptic scale. I may not be the first to speculate that the same principals can therefore be applied to the entire global atmosphere.
I accordingly decided a few years ago to begin to build an atlas of full atmosphere global maps because in part I was curious to see if QG-styled representations of features such as jet streams and vortexes would manifest. I also wondered how such a map would reflect other well known features as Hadley and Walker circulations, the Intertropical Convergence Zone (ITCZ), and the OLR along the equatorial west Pacific, as well as a few other intersections of global hydrological interest.
Figure 1 is a typical example of the types of data I graph in this light. This is a comparison of the full atmosphere geopotential height (Z) over the month of December at the end of 2005 and at the end of 2013. I downloaded the underlying data from an ERA Interim archive at a UCAR site over a year ago. The archive included the parameters of Temperature (T), Geopotential Height (Z), Divergence of Latent Energy (LEDIV), and Evaporation – Precipitation (EP), in addition to numerous other parameters, averaged or integrated across the full atmosphere.
Figure 1. Comparison of two months for coverage of QG winds and full atmosphere geopotential heights Z.
Figure 1 and many subsequent figures are based in part on my coarsening of the ERA Interim data. Each cell is 2.8125 degrees in latitude and longitude dimensions. The row and column axes reflect the cell counts accordingly. As mentioned, this figure compares the Z contours across the planet for the month of December at the end of 2005 and at the end of 2013. These years and months are not necessarily any more or less interesting than any other two months. I simply was initially motivated to compare Z for a month following a high Atlantic cyclone count season and for a month following a low count season. According to the HURDAT reference , the Accumulated Cyclonic Energy (ACE) record indicates that 2005 was a high energy season and 2013 was relatively low.
I have introduced streamline origin points at various locations across the map to help define flows and gyres more clearly than the underlying vector plots could do. These lines are calculated from the original ERA Interim full atmosphere zonal and meridional wind speed data. As these are excerpts from works in progress, the streamline origin and identification features and later parcel tracking features are not always consistent. For the most part, green streamlines originate along a meridian in the east Atlantic (yet west of the Greenwich Meridian). Cyan streamlines originate along a meridian in the west Atlantic. Black streamlines originate along the east Pacific, and blue lines originate along the central Pacific. Red lines originate along the Greenwich Meridian which also defines the left boundary of each of the maps.
Examinations of the resulting flow patterns appear to confirm the expected Hadley and Walker circulation related middle latitude westerlies, equatorial easterlies, polar vortices, jet streams, and gyres at the very least. One interesting artifact of the QG approach that I looked forward to observing was the inevitable singularities of both “sink” and “source” vortex features created automatically from this mapping of a 3D circulation to an essentially 2D surface.
Figure 1 documents a small number of QG transformed sources and sinks, some of which might be persistent across the years. Each source and sink vortex identified through the streamline coverages are largely understood to be QG artifacts and they are positioned at well known locations. “Sink” gyres appear in the polar regions and two types of “Source” gyres appear in sub equatorial regions. In my view, these more or less stationary gyre features and their arrangement with respect to the ITCZ are reminiscent of the previously mentioned and most curious QG representation of a jet stream and storm generation. But this is just an idle thought and perhaps it has already been more deeply explored by others.
From a conventional perspective, the gyres are simply giant rotating masses of air that are caused by horizontal shear between the mid latitude westerlies and the equatorial easterlies. A purely QG artifact of interest to me which is animated shortly, is that air parcels actually disappear into the sinks and reappear from the sources. That wouldn’t happen of course in the real world. Or would it? 😀
In addition to these fantastic artifacts, actual known weather events can easily be visualized fully automatically using this system. For example, the “Great Polar Vortex” of early 2014 can be seen in Figure 2. This is a good time to note that manually developed artworks are customarily used in depictions of items such as polar vortices and jet streams. Such renderings typically are motivated because the raw data depictions are not often clear. I think however that many would agree that these new automatic QG based maps appear to express more accurate fidelity to observations and…