Blanca Mendoza

Historical Droughts in Central Mexico and Their Relation with El Niño

A catalog containing an unprecedented amount of historical data in central Mexico, covering almost six centuries (1450–1900), is used. This is a catalog of agricultural disasters that includes events associated with hydrometeorological phenomena, or hazards, whose effects were mainly felt in the agricultural sector, such as droughts. An analysis of the historical series of droughts in central Mexico for the period of 1450–1900 is performed. Periods of frequent drought centered at the years 1483, 1533, 1571, 1601, 1650, 1691, 1730, 1783, 1818, and 1860 have been identified. In particular, droughts in Mexico City and northwest Mexico that were identified through poor tree-ring growth are included in the frequent drought periods obtained in this work. Moreover, it was found that droughts occurred in El Nino years mainly for events of very strong and strong strengths, at a significant level. Also, most droughts lasted for 1 or 2 yr. Last, by analyzing the periodicities of the drought time series it was found that those that are the most conspicuous are the quasi-bidecadal frequencies of 18.9 and 21 yr.

A study of historical droughts in southeastern Mexico

Abstract A catalog containing an unprecedented amount of historical data in the southeastern part of Mexico covering almost four centuries (1502–1899) is used to construct a drought time series. The catalog records information of agricultural disasters and includes events associated with hydrometeorological phenomena or hazards whose effects were mainly felt in the agricultural sector, such as droughts. An analysis of the historical series of droughts in southeastern Mexico for the period 1502–1899 is performed. The highest drought frequency occurred around the years 1650, 1782, and 1884; no droughts were reported around 1540, between 1630 and 1640, along the largest time lapse of 1672–1714, and between 1740 and 1760. From 1760 until the end of the period of study droughts definitively occur more often than they did from ∼1550 to 1760. In addition, most droughts lasted for 1–2 yr. Analyzing the frequencies of the drought time series it is found that the most conspicuous cycles are ∼3–4 and 7 yr, although ...

Estimations of Maunder Minimum solar irradiance and Ca II H and K fluxes using rotation rates and diameters

The total solar irradiance and Ca H and K fluxes (HK) for the Maunder minimum are estimated from scaling laws for solar-type stars using historical solar rotation rates and solar diameters. We found that the irradiance may be lower than modern solar minimum values by 1.23% in 1683 and by 0.37% in 1715. The estimate for 1683 is substantially lower than previously reported. Analysis of cosmogenic isotope records in ice cores and tree rings shows continuation of the Suns magnetic cycle through the Maunder minimum; therefore, we find the HK fluxes to be 0.161 for 1683 and 0.163 for 1715, compared with the modern solar minimum flux value of ~0.164. This suggests that the Sun never reached a noncycling state.

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.

Effects of solar activity on myocardial infarction deaths in low geomagnetic latitude regions

We study the effect of solar activity on the incidence of myocardial infarction deaths (MID) in Mexico. We work with 129,917 cases along 1996–1999, grouping the data by sex and age, and considering the solar cycle phases. At higher frequencies the circaseptan is the most persistent periodicity in MID occurrence. During solar minimum the circaseptan period is not detectable compared with solar maximum. During Forbush decreases and geomagnetic activity, most cases present a higher average MID occurrence. Furthermore the MID rate is higher as the level of the geomagnetic perturbation increases. Male MID rates are in general higher than female rates and the difference increases as the geomagnetic perturbation increases. The age group with the lowest MID incidence is 25 to 44 years, the age group of ≥65 years is the most vulnerable. We conclude that solar activity does affect MID at low geomagnetic latitudes and that the solar maximum is the most hazardous time for MID incidence.

On the Role of Large-Scale Solar Photospheric Motions in the Cosmic-Ray 1.68-YR Intensity Variation

Analysis of cosmic-ray intensity time evolution has led to the identification of intensity variations with several periodicities, most of them correlated with one or another phenomenon of the Sun. Recently Valdés-Galicia, Pérez-Enriquez, and Otaola (1996) reported on a newly-found 1.68-yr variation, which seems to be correlated with periodicities in X-ray long-duration events and low-latitude coronal hole area variations. As those phenomena are related with magnetic flux emergence and transport, in this paper we investigate the possible relationship of the referred cosmic-ray variation with characteristic times of different tracers of meridional circulation. Our results indicate that several of the calculated times might be related to the 1.68-yr cosmic-ray variation. A physical mechanism through which this connection may operate is discussed.

Electric currents induced inside biological cells by geomagnetic and atmospheric phenomena

An increasing number of studies have appeared in the last ten years indicating that some pathologies may correlate with geomagnetic activity and cosmic rays. However a physical mechanism binding both phenomena has not been proposed. In the present work we obtain the amplitude of the magnetic fields at different frequencies, that may induce inside biological cells currents of the same magnitude of the currents generated by the cells themselves. We compare these values with the wave amplitudes produced in geomagnetic and atmospheric phenomena, and found that micropulsations, whistlers and lightning are capable of produce the same or larger values.

SCALE-INVARIANCE OF NORMALIZED YEARLY MEAN GRAIN YIELD ANOMALY SERIES

In crop science, tools of non-linear dynamics, fractals, chaos, intermittency and self-organized criticality may be employed and applied to the analysis of spatial variability and temporal behavior of agro-meteorological variables, soil properties, plant attributes, commercial yields, and prices of the agricultural products in order to gain knowledge about underlying complex processes. A search on the occurrence of particular scaling laws in Mexicos normalized yearly mean grain yield anomaly series of maize (Zea mays L.), beans (Phaseolus vulgaris L.), wheat (Triticum aestivum L.) and rice (Oriza sativa L.), using a variography approach is reported in this work. Additionally, power spectrum determination, time-frequency analysis, and estimation of Lyapunov exponent were performed for each profile in order to obtain useful information on the frequency contents and signs at which important frequencies occur as well as to determine their sensitivity to initial conditions. Fractal analysis gives us the order maize

Solar Rotation And Cycle Length

A positive correlation is suggested between solar rotation rate and solar cycle length for cycles 12 to 20. This result seems to be opposite to recent observations in solar-type stars and the Sun and yields inverse correlations between cycle lengths and chromospheric activity, but it agrees with previous work with solar-type stars and the Sun suggesting a positive correlation between cycle length and rotation rate. Estimates of solar cycle length for the Maunder minimum suggest a length ∼17 yr.

Sensitivity of the surface temperature to changes in total solar irradiance calculated with the WRF model

Resumen En este trabajo se estima la sensibilidad de la temperatura del modelo WRF a cambios en la Radiacion Solar Total (RST). Las simulaciones se realizaron para una region centrada en el Atlantico norte, incluyendo partes del Este de Norteamerica, Oeste de Europa y Noroeste de Africa. Para esto, se realizaron 4 simulaciones iguales, donde el unico parametro que se modifico fue la RST. Adicionalmente, se realizo una quinta simulacion donde se cambiaron las condiciones iniciales atmosfericas, para comparar el efecto del cambio de la RST sobre la temperatura con el de un cambio en el dia de inicio de la integracion. Se compararon promedios mensuales de temperatura para cada simulacion obteniendose que tanto los cambios en las condiciones iniciales como los de la RST tienen un impacto medible en la temperatura de la region de estudio. Se presenta tambien una estimacion de la sensibilidad del modelo usando parametros adimensionales. Con estos experimentos numericos encontramos algunos rasgos que permitirian distinguir entre los efectos de cambios de la RST y en las condiciones iniciales sobre la temperatura. Sin embargo, los cambios debidos al RST son de la misma magnitud que los cambios debidos a las variaciones en las condiciones iniciales. Se observa tambien que, en promedio y sobre toda la malla, la temperatura promedio no sufre cambios significativos ni ante cambios de la RST ni ante los de las condiciones iniciales.Palabras clave: WRF, sensibilidad de la temperatura, radiacion solar total, Atlantico Norte, tecnica de parametros adimensionales.