143 research outputs found
Power-Law Persistence in the Atmosphere: Analysis and Applications
We review recent results on the appearance of long-term persistence in
climatic records and their relevance for the evaluation of global climate
models and rare events.The persistence can be characterized, for example, by
the correlation C(s) of temperature variations separated by s days.We show
that, contrary to previous expectations, C(s) decays for large s as a power
law, C(s) ~ s^(-gamma). For continental stations, the exponent gamma is always
close to 0.7, while for stations on islands gamma is around 0.4. In contrast to
the temperature fluctuations, the fluctuations of the rainfall usually cannot
be characterized by long-term power-law correlations but rather by pronounced
short-term correlations. The universal persistence law for the temperature
fluctuations on continental stations represents an ideal (and uncomfortable)
test-bed for the state of-the-art global climate models and allows us to
evaluate their performance. In addition, the presence of long-term correlations
leads to a novel approach for evaluating the statistics of rare events.Comment: 12 pages, 6 included EPS figures, added chapter
Phase Synchronization in Temperature and Precipitation Records
We study phase synchronization between atmospheric variables such as daily
mean temperature and daily precipitation records. We find significant phase
synchronization between records of Oxford and Vienna as well as between the
records of precipitation and temperature in each city. To find the time delay
in the synchronization between the records we study the time lag phase
synchronization when the records are shifted by a variable time interval of
days. We also compare the results of the method with the classical
cross-correlation method and find that in certain cases the phase
synchronization yields more significant results.Comment: 11 pages including 8 figure
Volatility in atmospheric temperature variability
Using detrended fluctuation analysis (DFA), we study the scaling properties
of the volatility time series of daily temperatures
for ten chosen sites around the globe. We find that the volatility is long
range power-law correlated with an e xponent close to 0.8 for all
sites considered here. We use this result to test the scaling performance of
several state-of-the art global climate models and find that the models do not
reproduce the observed scaling behavior.Comment: 10 pages, 3 figures. Accepted for publication in Physica
Appropriateness of correlated first order auto-regressive processes for modeling daily temperature records
The present study investigates linear and volatile (nonlinear) correlations
of first-order autoregressive process with uncorrelated AR (1) and long-range
correlated CAR (1) Gaussian innovations as a function of the process parameter
(). In the light of recent findings \cite{jano}, we discuss the choice
of CAR (1) in modeling daily temperature records. We demonstrate that while CAR
(1) is able to capture linear correlations it is unable to capture nonlinear
(volatile) correlations in daily temperature records.Comment: Accepted for publication in Physica
Comment on "Scaling of atmosphere and ocean temperature correlations in observations and climate models"
In a recent letter [K. Fraedrich and R. Blender, Phys. Rev. Lett. 90, 108501
(2003)], Fraedrich and Blender studied the scaling of atmosphere and ocean
temperature. They analyzed the fluctuation functions F(s) ~ s^alpha of monthly
temperature records (mostly from grid data) by using the detrended fluctuation
analysis (DFA2) and claim that the scaling exponent alpha over the inner
continents is equal to 0.5, being characteristic of uncorrelated random
sequences. Here we show that this statement is (i) not supported by their own
analysis and (ii) disagrees with the analysis of the daily observational data
from which the grid monthly data have been derived. We conclude that also for
the inner continents, the exponent is between 0.6 and 0.7, similar as for the
coastline-stations.Comment: 1 page with 2 figure
Long term persistence in the sea surface temperature fluctuations
We study the temporal correlations in the sea surface temperature (SST)
fluctuations around the seasonal mean values in the Atlantic and Pacific
oceans. We apply a method that systematically overcome possible trends in the
data. We find that the SST persistence, characterized by the correlation
of temperature fluctuations separated by a time period , displays two
different regimes. In the short-time regime which extends up to roughly 10
months, the temperature fluctuations display a nonstationary behavior for both
oceans, while in the asymptotic regime it becomes stationary. The long term
correlations decay as with for both
oceans which is different from found for atmospheric land
temperature.Comment: 14 pages, 5 fiure
Power-law persistence and trends in the atmosphere: A detailed study of long temperature records
We use several variants of the detrended fluctuation analysis to study the
appearance of long-term persistence in temperature records, obtained at 95
stations all over the globe. Our results basically confirm earlier studies. We
find that the persistence, characterized by the correlation C(s) of temperature
variations separated by s days, decays for large s as a power law, C(s) ~
s^(-gamma). For continental stations, including stations along the coastlines,
we find that gamma is always close to 0.7. For stations on islands, we find
that gamma ranges between 0.3 and 0.7, with a maximum at gamma = 0.4. This is
consistent with earlier studies of the persistence in sea surface temperature
records where gamma is close to 0.4. In all cases, the exponent gamma does not
depend on the distance of the stations to the continental coastlines. By
varying the degree of detrending in the fluctuation analysis we obtain also
information about trends in the temperature records.Comment: 5 pages, 4 including eps figure
Fractal Analysis of River Flow Fluctuations (with Erratum)
We use some fractal analysis methods to study river flow fluctuations.
The result of the Multifractal Detrended Fluctuation Analysis (MF-DFA) shows
that there are two crossover timescales at and
months in the fluctuation function. We discuss how the
existence of the crossover timescales are related to a sinusoidal trend. The
first crossover is due to the seasonal trend and the value of second ones is
approximately equal to the well known cycle of sun activity. Using Fourier
detrended fluctuation analysis, the sinusoidal trend is eliminated. The value
of Hurst exponent of the runoff water of rivers without the sinusoidal trend
shows a long range correlation behavior. For the Daugava river the value of
Hurst exponent is and also we find that these fluctuations have
multifractal nature. Comparing the MF-DFA results for the remaining data set of
Daugava river to those for shuffled and surrogate series, we conclude that its
multifractal nature is almost entirely due to the broadness of probability
density function.Comment: 13 pages, 10 figures, V2: Added comments, references and one more
figure, improved numerical calculations with new version of data, accepted
for publication in Physica A: Statistical Mechanics and its Applications. The
version with Erratum contains some notes concerning Ref. [58
Detecting Long-range Correlations with Detrended Fluctuation Analysis
We examine the Detrended Fluctuation Analysis (DFA), which is a
well-established method for the detection of long-range correlations in time
series. We show that deviations from scaling that appear at small time scales
become stronger in higher orders of DFA, and suggest a modified DFA method to
remove them. The improvement is necessary especially for short records that are
affected by non-stationarities. Furthermore, we describe how crossovers in the
correlation behavior can be detected reliably and determined quantitatively and
show how several types of trends in the data affect the different orders of
DFA.Comment: 10 pages, including 8 figure
Volcanic forcing improves Atmosphere-Ocean Coupled General Circulation Model scaling performance
Recent Atmosphere-Ocean Coupled General Circulation Model (AOGCM) simulations
of the twentieth century climate, which account for anthropogenic and natural
forcings, make it possible to study the origin of long-term temperature
correlations found in the observed records. We study ensemble experiments
performed with the NCAR PCM for 10 different historical scenarios, including no
forcings, greenhouse gas, sulfate aerosol, ozone, solar, volcanic forcing and
various combinations, such as it natural, anthropogenic and all forcings. We
compare the scaling exponents characterizing the long-term correlations of the
observed and simulated model data for 16 representative land stations and 16
sites in the Atlantic Ocean for these scenarios. We find that inclusion of
volcanic forcing in the AOGCM considerably improves the PCM scaling behavior.
The scenarios containing volcanic forcing are able to reproduce quite well the
observed scaling exponents for the land with exponents around 0.65 independent
of the station distance from the ocean. For the Atlantic Ocean, scenarios with
the volcanic forcing slightly underestimate the observed persistence exhibiting
an average exponent 0.74 instead of 0.85 for reconstructed data.Comment: 4 figure
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