Rosa Hilda Compagnucci

A Quantitative Model of Magnetic Enhancement in Loessic Soils

We present a quantitative model for the climatic dependence of magnetic enhancement in loessic soils. The model is based on the widely accepted hypothesis that ultrafine magnetite precipitates during alternating wetting and drying cycles in the soil micropores. The rate at which this occurs depends on the frequency of drying/wetting cycles, and on the average moisture of the soil. Both parameters are estimated using a statistical model for the soil water balance that depends on frequency and intensity of rainfall events and on water loss by evapotranspiration. Monthly climatic tables are used to calculate the average soil moisture and the rate of pedogenic magnetite production, which is proportional to a new parameter called magnetite enhancement proxy (MEP). Our model is tested by comparing MEP calculated for known present-day climates with the magnetic enhancement of modern soils. The magnetic enhancement factor, defined as the ratio between a given magnetic enhancement parameter and MEP, is expected to be a site-independent constant. We show that magnetic enhancement differences between soils from the Chinese Loess Plateau and from Midwestern U.S. are explained by our model, which yields similar magnetic enhancement factors for the two regions. Our model is also successful in predicting the mean annual rainfall threshold above which magnetic enhancement declines in a given type of climate.

The 1976/77 Austral Summer Climate Transition Effects on the Atmospheric Circulation and Climate in Southern South America

Previous works suggest that more El Nino–like conditions can be expected over the South American (SA) climate and atmospheric circulation because of the similarity of the predominately warm conditions in the sea surface temperature (SST) over the central-equatorial Pacific after the 1976/77 summer with those of the SSTs during El Nino events. Here, the summer (October to March) low-level atmospheric circulation over southern SA is studied in order to determine the specific changes that can be related with the global climate transition 1976/77. The rotated principal component analysis is applied to the daily 850-hPa geopotential height fields from the NCEP–NCAR reanalysis I for the periods before and after 1976/77. The second and third principal patterns reveal changes both in the order of explained variances and in some of their spatial features. They can be associated with an expansion of the subtropical South Atlantic anticyclone over SA and lower midlatitude cyclone activity after the 1976/77 summer. The latter is partly associated with the actual tendency toward the positive phase of the southern annular mode. The main patterns can even explain some changes in the observed precipitation over subtropical central-west Argentina as well as for other subtropical regions. Different inhomogeneity tests applied to the atmospheric circulation climatology support the changes. Results suggest that the atmospheric circulation change could be somewhat unique (not observed in the twentieth century) and, thus, it could not be thoroughly ascribed to the El Nino–like variability.

Central-West Argentina Summer Precipitation Variability and Atmospheric Teleconnections

AbstractThe interannual-to-multidecadal variability of central-west Argentina (CWA) summer (October–March) precipitation and associated tropospheric circulation are studied in the period 1900–2010. Precipitation shows significant quasi cycles with periods of about 2, 4–5, 6–8, and 16–22 yr. The quasi-bidecadal oscillation is significant from the early 1910s until the mid-1970s and is present in pressure time series over the southwestern South Atlantic. According to the lower-frequency spectral variation, a prolonged wet spell is observed from 1973 to the early 2000s. The precipitation variability shows a reversal trend since then. In that wet epoch, the regionally averaged precipitation has been increased about 24%. The lower-frequency spectral variation is attributed to the climate shift of 1976/77.From the early twentieth century until the mid-1970s, the precipitation variability is associated with barotropic quasi-stationary wave (QSW) propagation from the tropical southern Indian Ocean and the South P...

Dynamical characterization of the last prolonged solar minima

The planetary hypothesis of the solar cycle is an old idea in which the gravitational influence of the planets has a non-negligible effect on the causes of the solar magnetic cycle. The advance of this hypothesis is based on phenomenological correlations between dynamical parameters of the Sun’s movement around the barycentre of the Solar System and sunspots time series; and more especially, identifying relationships linking solar barycentric dynamics with prolonged minima (especially Grand Minima events). However, at present there is no clear physical mechanism relating these phenomena. The possible celestial influence on solar cycle modulation is of great importance not only in solar physics but also in Earth sciences, because prolonged solar minima have associated important climatic and telluric variations, in particular, during the Maunder and Dalton Minimum. In this work we looked for a possible causal link in relation with solar barycentric dynamics and prolonged minima events. We searched for particular changes in the Sun’s acceleration and concentrated on long-term variations of the solar cycle. We show how the orbital angular momentum of the Sun evolves and how the inclination of the solar barycentric orbit varies during the epochs of orbital retrogressions. In particular, at these moments, the radial component of the Sun’s acceleration (i.e., in the barycentre-Sun direction) had an exceptional magnitude. These radial impulses occurred at the very beginning of the Maunder Minimum, during the Dalton Minimum and also at the maximum of cycle 22 before the present extended minimum. We also found a strong correlation between the planetary torque and the observed sunspots international number around that maximum. We apply our results in a novel theory of Sun–planets interaction that it is sensitive to Sun barycentric dynamics and found a very important effect on the Sun’s capability of storing hypothetical reservoirs of potential energy that could be released by internal flows and might be related to the solar cycle. This process begins about 40 years before the solar angular momentum inversions, i.e., before Maunder Minimum, Dalton Minimum, and before the present extended minimum. Our conclusions suggest a dynamical characterization of peculiar prolonged solar minima. We discuss the possible implications of these results for the solar cycle including the present extended minimum.

Eastern Patagonia Seasonal Precipitation: Influence of Southern Hemisphere Circulation and Links with Subtropical South American Precipitation

AbstractSome aspects of the seasonal precipitation over eastern Patagonia, the southernmost area of South America east of the Andes Cordillera, are examined in this paper. Results indicate that the central-north areas, the southern continental region, and the southernmost islands are three independent regions of seasonal precipitation, and that each of them is associated with specific patterns of atmospheric circulation. Precipitation over the central-north region is significantly related to the precipitation over a wide area of southern South America east of the Andes during the four seasons. Enhanced (reduced) precipitation over this area is associated with weakened (intensified) westerly flow in the region. Precipitation over the southern continental area has a close connection with the dipolar pattern of precipitation over subtropical South America during spring, summer, and autumn. The anomalies of atmospheric circulation at low and upper levels associated with the subtropical dipole are also able to...

On the variability of seasonal temperature in southern South America

The aim of this paper is to investigate different aspects of the seasonal-to-interannual temperature variability in Eastern Patagonia, the southernmost area of South America, east of the Andes Cordillera. Homogenous regions of seasonal variability and the atmospheric circulation patterns associated with warm and cold conditions in each of them are described in this study. Relationships between temperature in Eastern Patagonia and that registered in other areas of southern South America are also addressed. Results show that the northern and southern areas of Eastern Patagonia have different temperature variability in summer and autumn whereas the temperature variability tends to be more homogeneous within the region during winter and spring. Warm (cold) conditions in the northern areas are associated with reinforced (weakened) westerlies in summer, winter and spring whereas northerly (southerly) advections of warm (cold) air toward the region produce such conditions in autumn. Temperature in the southern portion of Eastern Patagonia is affected by anticyclonic (cyclonic) anomalies that enhance (reduce) the incoming solar radiation and induce reinforced (weakened) westerlies promoting warm (cold) conditions in the region. Furthermore, cyclonic (anticyclonic) anomalies at subpolar latitudes hinder (favor) outbreaks of cold air increasing (decreasing) the temperature over areas of Eastern Patagonia. The circulation anomalies associated with warm (cold) conditions in Eastern Patagonia also promote cold (warm) conditions over areas of northern Argentina, Paraguay and southern Brazil. Consequently, a dipole of temperature is detected in southern South America with centers of opposite sign over these regions.

Removal of Systematic Biases in S-Mode Principal Components Arising from Unequal Grid Spacing

Frequently, physical variables are analyzed using gridded fields, on regular latitude‐longitude frameworks. Such networks often concentrate a disproportionate number of observations over polar regions. If these types of grids are used for an S-mode principal component analysis, they produce a bias of the component patterns toward the temporal patterns observed at higher latitudes. A method to potentially eliminate this effect, while employing the covariance similarity matrix, is to weight the variables by the square root of the cosine of the latitude of the point at which the datum was observed. However, this processing is not useful when using the correlation similarity matrix. In this case, a spatially uniform or equal density grid can be designed by means of the criteria of a constant density of points in each circle of latitude. Then, the variable values are linearly interpolated into this new equal-density grid. This technique is easy to program and to adapt to any regular latitude‐longitude network. As an example, an application of the technique is presented for monthly anomalies of 70-hPa temperature data collected by the Microwave Sounding Unit (MSU) flown on board the NOAA Television Infrared Observation Satellites (TIROS-N). A regular latitude‐longitude network generates an overestimation of the polar area significance with respect to those obtained by the equal-density criterion. By comparing two sets of point distributions, it is shown that the representative patterns of the temporal evolution of the variables at low or midlatitudes are modified little, if any, by creating a network of equal density points. Nevertheless, changes may be observed in the explained variances because the eigenvalues are impacted directly to the change in the number of points in the networks caused by processing a non-equal-density grid to the equal-density one.

Impact of ENSO Events on the Hydrological System of the Cordillera de los Andes during the last 450 Years

The correlation between river runoff and ENSO-events in the Cuyo region, western Argentina was studied. It could be shown that most “wet” years are associated with an ENSO- event (preceding or same year) while only about 67 percent of ENSO events cause high river runoff in the study-area. Thus ENSO is one, but not a definite criterion for high precipitation/ high river runoff.

Spatial fields of Antarctic sea-ice concentration anomalies for summer-autumn and their relationship to Southern Hemisphere atmospheric circulation during the period 1979-2009

Abstract Summer–autumn monthly sea-ice concentration anomaly (SICA) fields in Antarctica obtained from satellite data for the period 1979–2009 were analysed with Varimax-rotated T-mode principal component analysis (PCA). the first three PCA scores described the SICA spatial behaviour and explained 38.07% of the total variance. the related atmospheric circulation characteristics were analysed using 850 hPa height and surface air-temperature anomalies for the months clustered by the corresponding SICA composites, which were based on PCA loadings above a ±0.3 threshold. the principal characteristics of SICA can be seen between the Ross and Weddell Seas, areas that remained ice-covered during the analysis period. Elsewhere around Antarctica, small distinct characteristics occur mostly in embayments. the leading summer–autumn SICA pattern shows a structure with two centres of equal sign located one over the Weddell and the other over the Ross Sea–southwest Pacific Ocean sector and a centre of opposite sign over the Bellingshausen and Amundsen Seas. the second SICA pattern is represented by a dipole over the Weddell Sea as a result of an increase (decrease) in sea-ice concentration in the northern sector (positive phase) and a decrease (increase) in the southern region, together with a positive (negative) centre over the Ross and Amundsen Seas. the latter pattern is characterized by equal-sign anomalies on both sides of the Antarctic Peninsula and opposite-sign centres all around Antarctica with the highest intensity over the Ross Sea.

Modeling the Atmospheric Circulation and Climatic Conditions over Southern South America During the Late History of the Gondwana Supercontinent

The different processes responsible for climate and atmospheric circulation forcing and their relevance on the general circulation of the Southern South America together with the conditions over Patagonia, for the period of the Gondwana supercontinent, are identified in this chapter. During the history of this supercontinent, the main paleoclimate forcings were as follows: (1) the continental drift that affected latitude, elevation, and topography; (2) changes in the amount of greenhouse gases in the Earth’s atmosphere; and (3) volcanic activity. The paleoatmospheric circulation is analyzed in special sections according to age, Early Triassic to Early Jurassic, Middle to Late Jurassic, and Cretaceous, accordingly with the key changes in the ocean–land distribution and locations of the continents. Different paleoclimatic modeling scenarios through the periods are reviewed and compared with proxy data. From both sources of information, it arises that the opening of the Hispanic Corridor and the formation of the Atlantic Ocean were the chief factors that produced the strong climatic changes registered from the Triassic to the Cretaceous and the remarkable difference with current climate conditions. Other important factors were the variations in the volume of greenhouse gases, especially CO2, which is related to volcanic activity and changes in the heat transport through the oceans. The observed results suggest that strong monsoon conditions dominated this period of the Gondwana supercontinent. However, there are large differences with respect to the impact of the various climatic forcings between model simulations of circulation general conditions in the Cretaceous. An extensive list of references provides detailed and updated information on the topics covered in this chapter.