Dolores Maravilla

FRACTALITY OF MONTHLY EXTREME MINIMUM TEMPERATURE

Interest in climate change has increased over the last 30 years due largely to global predictions associated with the greenhouse effect, which appear to lead to a substantial increase in planetary temperature. Implications of such results have led many scientists to examine climatic records from different regions of the world in order to understand temperature behavior. However, many researchers have noted that changes in temperature variability are also important in determining the future temperature distributions. In this context, we have analyzed a long-term record of monthly extreme minimum temperature registered at Guanajuato, Mexico. Data set was treated as a fractal profile to estimate the fractal dimension through variography (Dv) and power-spectral (Ds) approaches under two situations: (1) complete series, from January 1895 to December 1997 with 312 missing observations, and (2) partial series, from January, 1921 to April, 1963 with no missing values. In both cases, we obtained similar values for the two types of fractal dimensions meaning there is not a significant effect of missing values. The estimated fractal dimensions for the partial series (508 observations) are near 1.5 (Dv = 1.445 ± 0.06, Ds = 1.486 ± 0.155), which means monthly extreme minimum temperature is almost equally characterized by both short- and long-range variations. Evaluating through scaling arguments did not evidence multifractality in the scale range of two to 254 months. Then interpolation can make use of the fact that monthly extreme minimum temperature has a power-law spectrum. Interpolated data generated by this way may develop greater confidence in their capability to forecast near future climate.

Temperature variability in central Mexico and its possible association to solar activity

Abstract Minimum extreme temperature variability from five meteorological stations in the central part of Mexico covering a period from ∼1920 to ∼1990 is examined. We found a correlation coefficient (r=0.65) between these temperature records and geomagnetic activity. Furthermore, by performing spectral analysis peaks were obtained with similar periodicities to those found in the sunspot number, the magnetic solar cycle, cosmic ray fluxes and geomagnetic activity; all of these phenomena are modulated by solar activity. Signals with periodicities comparable to those observed in El Nino and the Quasi-Biennial Oscillation were also identified. We conclude that the solar signal is probably present in the minimum extreme temperature record of the central part of Mexico.

Spectral analysis results for sudden storm commencements 1868–1996

Abstract We perform a power spectrum analysis of the occurrence of sudden storm commencements for solar cycles 11 to 22. Studying in particular peaks longer than the 11 years solar cycle, we found a significant periodicity at around 20 to 30 years, which seems to be unstable. Similar three-cycle unstable peaks are observed in other solar and geomagnetic phenomena such as sunspots, auroral occurrence and the Ap index. The origin of such a periodicity in the occurrence of storm commencements is unknown at present. Due to its unstable behaviour it is not possible to predict when it will appear in the SSCs data.