The atmospheric heating patterns: a new heat transport perspective
File(s)
Author(s)
Liang, Minyi
Type
Thesis
Abstract
The standard definition of poleward heat transport was found to lead to surprisingly large fluctuations (in excess of $10^{15}$W = 1PW) on timescales shorter than a few years. We have argued in this thesis the standard definition masks more meaningful climate signals present in the heat transport variability, and a new definition is proposed to isolate the latter.
Utilising the new definition of heat transport, large/weak heat transport events are identified. The atmospheric heating patterns by the mean flow and eddies under these enhanced heat transport events are also discussed. It is found that for every 1PW increase in heat transport across $45^\circ$ latitude, a surface heating and cooling dipole at the rate of about 0.3 K/day is observed. This is largely attributed to stationary (transient) eddies in the NH (SH). The same dipole structure is noticeable in the upper troposphere but tilted towards the pole when analysing the heating patterns by eddies (but is partially compensated by the mean flow). This tilted dipole might be linked to poleward energy propagation. For the sub-tropics, when the atmosphere carries more heat across $10^\circ $ latitude, a vertically coherent heating/cooling, extending from the surface to the upper troposphere, is observed, with values being about $\pm$ 0.5K/day. This heating pattern is closely linked to the strengthening of the Hadley circulation.
Using the standard definition of heat transport, similar heating patterns are also found, although the magnitude is much smaller. This further confirms our hypothesis that the new definition may shed further light on the intuitive link between energy transport and climate variability.
The above analysis is carried out under the Eulerian mean framework. Next, we analyse the cancellation effect between the mean flow and eddies using the three most popular frameworks under pressure coordinates: the Eulerian mean, the conventional transformed Eulerian mean, and the modified transformed Eulerian mean. It is found that the choice of framework largely depends on the domain one is interested in, and there is no one framework that is more favourable than the others. We further conclude that Eulerian mean framework is adequate for the analysis of the heating patterns under enhanced heat transport events as discussed in this thesis.
Utilising the new definition of heat transport, large/weak heat transport events are identified. The atmospheric heating patterns by the mean flow and eddies under these enhanced heat transport events are also discussed. It is found that for every 1PW increase in heat transport across $45^\circ$ latitude, a surface heating and cooling dipole at the rate of about 0.3 K/day is observed. This is largely attributed to stationary (transient) eddies in the NH (SH). The same dipole structure is noticeable in the upper troposphere but tilted towards the pole when analysing the heating patterns by eddies (but is partially compensated by the mean flow). This tilted dipole might be linked to poleward energy propagation. For the sub-tropics, when the atmosphere carries more heat across $10^\circ $ latitude, a vertically coherent heating/cooling, extending from the surface to the upper troposphere, is observed, with values being about $\pm$ 0.5K/day. This heating pattern is closely linked to the strengthening of the Hadley circulation.
Using the standard definition of heat transport, similar heating patterns are also found, although the magnitude is much smaller. This further confirms our hypothesis that the new definition may shed further light on the intuitive link between energy transport and climate variability.
The above analysis is carried out under the Eulerian mean framework. Next, we analyse the cancellation effect between the mean flow and eddies using the three most popular frameworks under pressure coordinates: the Eulerian mean, the conventional transformed Eulerian mean, and the modified transformed Eulerian mean. It is found that the choice of framework largely depends on the domain one is interested in, and there is no one framework that is more favourable than the others. We further conclude that Eulerian mean framework is adequate for the analysis of the heating patterns under enhanced heat transport events as discussed in this thesis.
Version
Open Access
Date Issued
2019-05
Date Awarded
2019-09
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Czaja, Arnaud
Sponsor
Kristian Gerhard Jebsen Foundation
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)