Kenneth M Towe

I will appreciates comments from scholars that can help to supply relevant information on this topic.

Thank you

Very interesting. I was unaware of the "widening of the tropical belt with time". You are probably aware of this paper published in nature in 2008: "Widening of the tropical belt in a changing climate". It's been cited 671, so I recommend looking at the recent citations as a way to see what work has been done since. As far as I understand it, the widening of the tropical belt would be a response to increased SSTs that would extend the branches of the Brewer-Dobson circulation. This would mean stronger convection at the equator, increased divergence in the stratosphere, and the advection of mass expanding closer towards the poles. The terminal point of this would be the latitude at which the meridional component tends to zero. You would see a higher tropopause in the widening scenario, which, if impacts at the extratropics are ignored, would result in a steeper gradient of the tropopause height from pole to equator.

If we assume that the all extratropical impacts are negligible or ignored, then we could imagine a scenario where the north-south temperature gradient would increase, the jet streams closer to the poles as a result equatorial widening, and an increase in overall strength of the jet stream. It's not clear, however, that the jet stream is moving towards the poles, however, and the poles are warming at the same time the equator is warming (i.e. elevated SSTs and perhaps changes in cloud cover). As a result, we don't have a stronger jet nor do we have a stronger temperature gradient. In fact, it has been shown that the east-west component of the jet stream is slowing down and that the patterns are becoming more wavy. This results in more heat, energy, and mass transport between the poles and the equator. This explains why Alaska has been considerably warmer than D.C. at times when these patterns occur, and that the frequency at which this occurs has increased. The base state, zonal average may show this widening problem, but one should never ignore the extratropics when it comes to this problem, especially the interactions between the two.

Edward J. Strobach thank you for your comments. I know some of the things you stated about the effects of the widening of the tropical belts. However what can be done to curtail future or continuous widening?

Kenneth M Towe

Emmanuel, it's impossible to really say what would curtail future or continuous widening, and it's also very difficult to predict how much widening the equatorial region would experience over time. The first thing is to separate natural variability v. anthropogenic, and then from there understand the interaction and feedbacks between them. Second, there is a lagtime in the atmosphere, so you would need to understand atmospheric response to changes introduced into the system. Third, if you have the ability to run long-term climate forecasts, then you can try creating scenarios where you change or turn off forcing components so that you can see the impact on the widening problem. This would likely require a lot of different tests to see how a combination of different conditions/forcing results in the widening/narrowing of the tropical belt. Lastly, take a look at this problem when the ozone hole was reaching it's maximum v. the recent and gradual repair of the ozone hole. The ozone hole or lack of an ozone hole effects the lower stratospheric and upper tropospheric thermodynamics which would in turn effect the overall global circulation. Hope this provides some context and direction

Kenneth M Towe