Dominant Imprint of Rossby Waves in the Climate Network

The connectivity pattern of networks based on ground level temperature records shows a dense stripe of links in the extra tropics of the southern hemisphere. We show that statistical categorization of these links yields a clear association with the pattern of an atmospheric Rossby wave, one of the major mechanisms associated with the weather system and with planetary scale energy transport. It is shown that alternating densities of negative and positive links are arranged in half Rossby wave distances around 3500, 7000, and 10 000 km and are aligned with the expected direction of energy flow, distribution of time delays, and the seasonality of these waves. In addition, long distance links that are associated with Rossby waves are the most dominant in the climate network.

Figure 1

(a) An example of a seasonally detrended surface temperature daily time series from 45°S, 52.5°E for the year 1948. (b) Same as (a) for 45°S, 97.5°E. (c) The cross-correlation function between the time series shown in (a) and (b). (d) Same as (c) but when the time series of the two sites are of different years (“shuffling” method).

Figure 2

(a) The PDF of the mean weight of negative links in the globe, in real (solid line) and shuffled (dashed line) data. (b) The dependence of the std. of time delay ${\tau }^{*}$ on the mean weight $⟨W⟩$ for all possible links, for real [dark gray (blue)] and shuffled [light gray (red)] data. (c) The mean negative link weight as a function of distance $d$, for the SH (circles), the NH (squares), and the equatorial (diamonds) regions. The figure is based on the globe temperature records at 1000 hPa isobar for November to February.

Figure 3

The dependence of the weight of negative links on the distance $d$ in the SH during (a) winter and (b) summer. (c),(d) Same as (a),(b) for positive links. The PDF of time delays ${\tau }^{*}$ of near negative (squares, $d\sim 3500\mathrm{km}$), far positive (circles, $d\sim 7000\mathrm{km}$), and far negative (diamonds, $d\sim 10000\mathrm{km}$) weighted links, in the SH during (e) winter and (f) summer.

Figure 4

The out degree (a) and in degree (b) of the climate network structure from November to February (SH summer). The out degree (c) and in degree (d) of the climate network structure from May to August (SH winter). The specific region of outgoing and incoming links indicates eastward “network flow,” similar to Rossby waves traveling on top of an eastward jet.

Figure 5

The dependence of the weight of negative links on the distance $d$ in the SH during the SH summer months for temperature (left panels) and meridional velocity (right panels) for 300 hPa (upper panels) and 1000 hPa (lower panels).