Planetary waves or confirmation bias?

While in Oklahoma this academic year, I thought I had discovered something peculiar. Frequently, when discussing the weather back at home in Stockton-on-Tees with my parents via Skype, there was often a coincidence of weather type, even a swift change on the same day, e.g. the passage of a front. Of course, I was wary of psychological effects here – I believe they call it confirmation bias – or some positive version of Sod’s Law (“oh typical, it’s sunny at home and it’s 35ºC here!”). While trying to attempt to explain this to myself with recently-learned meteorological theory, I stumbled upon the fact that the distance between Norman, OK and Stockton-on-Tees, UK (7238 km) was rather close to the wavelength of a Rossby, or planetary, wave (6-7000 km, with some assumptions and a sinusoidal wave equation). Troughs in the planetary waves are associated with cyclonic (positive) vorticity advection downstream, and thus depressions, rain, wind etc., while ridges are manifested at the surface downstream by calm, anticyclonic conditions, thanks to widespread sinking motion under anticyclonic (negative) vorticity advection. Could this account for an occasional perceived parallel weather pattern?

It seems even the layman (or laywoman in this case) may inadvertently acknowledge this effect. After visiting my Grandma, a retired parcel van driver in Motherwell, Scotland, over the Christmas break, she remarked how she had foreseen a couple of the more severe snow days in the UK, because the US coast had been hit by a vicious nor’easter the day before. Her theory was that the low pressure moved across the Atlantic and hit the UK the next day. Should her perception be sound, a much more likely (and realistic) explanation is that troughs in the Rossby wave had been located over the eastern US and western Europe simultaneously.

I don’t think a quick delve into weather archives on randomly selected days would do justice to this ‘theory’, as I could easily pick three or four days to support my case and ignore the other times where it’s been hot in the Mid-West and, well, British in Britain. Instead, I throw this out to those much better qualified than myself: does this blog’s content sound reasonable to you? Have there been any papers on the matter? In the meantime, assuming my hypothesis holds, I shall continue to harbour pity for Americans in the Central Time Zone who are by my reckoning getting some pretty serious drizzle.

2 thoughts on “Planetary waves or confirmation bias?

  1. Yes, I think this is quite possible. The first thing I thought of was baroclinic waves, but these seem to have too short a wavelength, around 4000-5000km. (There’s a good paper on this by Chang and Yu 1999). So it would have to be longer Rossby waves. There are certainly lots of those about, but it’s not so clear that these have a preferred wavelength. For the UK and Oklahoma to often be the same we would need 7000km waves to happen more often than waves of other wavelengths. There does seem to be some evidence for this though – Branstator (2002) and Rennert and Wallace (2009) both show waves of this wavelength are pretty common….

    Branstator (2002) Circumglobal teleconnections, the jet stream waveguide, and the North Atlantic Oscillation, J. Climate

    Chang, E.K.M., and D.B. Yu**, 1999: Characteristics of wave packets in the upper troposphere. Part I: Northern hemisphere winter. J. Atmos. Sci., 56, 1708-1728.

    Rennert and Wallace (2009) Circumglobal teleconnections, the jet stream waveguide, and the North Atlantic Oscillation, J. Atmos Sci

Leave a Reply

Your email address will not be published. Required fields are marked *