Study of downward longwave radiation on the decadal scale: investigation of multifractal characteristics and long-term memory

Abstract

Οι χρονικές διακυμάνσεις της καθοδικής ακτινοβολίας μεγάλου μήκουσ κύματος μελετώνται με χρήση της μεθόδου MF-DFA.

We study the time fluctuations of Downward Longwave Radiation (DLR) using Multi-Fractal De-trended Fluctuation Analysis (MF-DFA) in decadal scale. In most stations non-stationary signal isobserved for micro-scales, comparable to those of meteorological processes. DLR presents power lawscaling for time scales of about ten days to five years. These different scaling regions are delimited fromthe emergence of a crossover that marks the transition to a positively correlated signal referred to aslong-memory. In several stations presenting the common feature of strong maritime influence, fluctua-tion function follows 1/f noise in micro-scales. These stations’ fluctuations are most likely affected byoscillatory trends. This is revealed by examining second order fluctuation function F2 (s) and furtherconfirmation is derived from multifractal analysis where scaling exponents spectrum is corrupted in atypical way, characteristic of periodicities presence. In west Pacific equatorial stations periodicity seemsto be ENSO, though this cannot be clearly considered a fact. In stations where no obvious oscillatorytrend is observed for F2 (s), mean memory is 0.63. Dependence of fluctuations scaling exponents on theorder q approaches the therotical behavior for Gaussian data. Deviations possibly occur due to shortrange correlations embedded in the data.