As we welcome winter, I want to take this oppotunity to share some research I’ve been doing on some certain aspects that have been shown to have an effect on Australian snow. Firstly the long term updates will be beginning very soon (this or next weekend). Secondly, thank you to all of those who read my Seasonal outlook, I got quite a few suggestions for next time, which I will certainly build upon. As I have said before, this is a evolving blog and place, and the forecasting world is constantly changing to account for new data.
There are various well known climate drivers like the El Niño Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), Southern Annular Mode (SAM) and the Madden-Julian Oscillation (MJO). These all affect Australian snowfall, as well as each other. They also affect global weather patterns in general as well.
This article concerns the effects of the Global Wind Oscillation (GWO) and the Global Integrated Atmospheric Angular Momentum (GLAAM or AAM). What these terms refer to is the winds of the planet being weaker (less westerly than normal) in terms of a low or negative AAM, and the winds of the planet being stronger (more westerly than normal) in terms of a high or positive AAM. In general, the jetstreams of both hemispheres are more poleward and contracted in a low AAM, and more equatorward and expanded in a high AAM.
So how does this connect to our continent? The GWO and AAM is influenced by ENSO and the MJO, and then back to them in a feedback loop. In general, a negative or low AAM means that there is a La Niña around, and a positive or high AAM means that there is an El Niño around. But there are often breaks with this correlation, like all correlations do. The MJO is responsible for about 25% of the GWO’s effects, the rest is eddy wave flux/transport, torques and other equatorial waves. The correlations between the GWO and MJO are summed up well in the below chart.
Generally when the MJO is in Phase 5/6, which are accepted as the best Phases for Australian snowfall, the AAM is neutral or rising into positive AAM territory, depending on various factors, including the mentioned ENSO factors. When the GWO is rising, the convection in the tropics is around Maritime Continent (Indonesia region), just north of Australia. And when it is falling, the convection is typically over Africa, moving into the Indian Ocean. In general GWO Phases 2&3 are for Low AAM, and GWO Phases 6&7 are for High AAM.
The torques I mentioned earlier are divided into Mountain Torque and Frictional Torque, and a bunch of smaller ones. Mountain Torque is created when the winds hit the mountains. +MT helps increase the winds, and -MT slows them down. Frictional Torque is similar but the torque is created as the wind scrapes the Earth’s surface, rather than by hitting a mountain range. There is a lot of complicated science around the torques and how they get affected by the MJO, and numerous other factors, but the above is a basic summary.
So how exactly does the GWO/AAM affect Australia? Well it turns out it has quite an effect. I compared the GLAAM dataset(spreadsheet fun!)from the NOAA ERSL Physical Sciences Division, and the Spencer’s Creek snowdepth measuring site, the generally accepted marker for snowfall in Australia, and the state of New South Wales in particular. Below is the raw correlation between the two.
So there is a 5% correlation between Australian snowfall and the GLAAM. A -AAM causes more snowfall to occur in the Australian Alps. Other drivers like SAM, MJO and ENSO have higher correlations, but given they are affected by the AAM/GWO themselves, the GWO is still an important tool. There is also the hampers of data analysis to contend with, outliers, errors, etc.
In other correlations, the GWO also relates to Australian weather and climate as a whole, as well as global climate in general. I analysed this in a 500mb plot from the NOAA, based upon the years that were above +1 in GLAAM and below -1 in GLAAM.
500mb anomaly plot, +1 and above GLAAM years.
500mb anomaly plot, -1 and below GLAAM years.
So it is clear there is a correlation between -AAM and troughing in SE Australia, where the major ski resorts are located. And there is also a correlation between +AAM and ridging in SE Australia.
The rest of the physical elements align with this theory (thanks for Dr Ed Berry for assisting me with this). He and Dr Klaus Weickmann were one of the first to make this theory more available to the public and to research it further, and correlate it with various global weather events. Their article here is one of the studies that the GWO and GLAAM under the Global Synoptic-Dynamic Model was formed under.
Victor Gensini is a research partner of Berry, and he has formed a very useful site for those who want to track the GLAAM and it’s potential impacts on Australian snowfall.
So in conclusion, I have shown that the Global Wind Oscillation is correlated with Australian snowfall. A negative Atmospheric Angular Momentum correlates with more troughing and snowfall in SE Australia. And a positive AAM correlates with ridging and less snowfall. It is a useful tool in accordance with the MJO and the SAM, primarily because you can forecast it up to a month away with some degree of accuracy. It isn’t perfect, but I think it is major step in long term forecasting for the Australian snow landscape. The GWO is the MJO’s extratropical partner for predicting snowfall on the long term. I am going to use it for sure to help predict the winter ahead.
Other links for further research:
In addition, the 33andrain forum hosts a teleconnection research portal, that lists dozens, if not hundreds of articles on teleconnections, such as the GWO, SAM, AAM, etc. Here is a link to it (note: you will need to sign up to the forum).
Thanks to all of those who read this article. I think this work was important, so I dedicated a lot of time towards it. I hope you enjoyed the read, and learnt something. If you have a comment, or are confused, feel free to drop a comment. Until next time, stay cool!