Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

Analysis of observations of the Loop Current (LC) northward penetration and LC area, from satellite sea surface temperature, Topex/Poseidon (TP) sea surface height anomaly, and results from numerical simulations shows that when a relatively large cyclone remains north of the LC, the shedding period between two consecutive eddies may increase. It is shown that the interaction between the LC and the cyclone produces leakage of mass from the current and pushes the LC towards the West Florida Shelf escarpment, where mass is also redistributed due to the generation of a pressure gradient and a jet along the shelf edge. This process delays the northward penetration of the LC and the enlargement of its area, increasing the time between eddy shedding. This happened in 1998, when the largest registered period between eddy shedding since 1973 occurred, and the largest cyclone of the TP era was north of the LC.

In some arid land, the irrigated fields are not contiguous and are surrounded by large patches of bare land. During the summer time and rainless season, the solar radiation flux is high and the surface temperature during daylight in the dry bare areas, is much higher than that of the air. The sensible heat generated over these areas may be advected to the irrigated fields. The crops are usually planted in rows and the irrigation systems used (trickle) do not wet the whole surface, the dry bare soil between the rows may develop high soil surface temperatures and lead to convective activity inside the canopy above the bare soil. Advection from the surrounding fields and convective activity inside the canopy affect the layer above the crop. We studied the surface layer above an irrigated tomato field planted in Israel´s Negev desert. The crop was planted in rows, trickle irrigated and the distance between the outer edges of two adjacent rows was 0.36 m at the time of measurement. The gradients in temperature and water vapor pressure were obtained at various heights above the canopy using a Bowen ratio machine. The residual in the energy balance equation was used as a criterion to determine the equilibrium layer. During the morning, unstable conditions prevail, and the equilibrium layer was between Z/h ~ 1.9 and 2.4. In some particular circumstances, in the late morning, the bare soil between the rows reached extremely high temperatures and during conditions with low wind speeds free convection was identified. During these hours the ‘‘residuals’’ of the energy budget to the heights Z/h = 1.5 and 2.4 were significantly different from zero and an extremely large variability was evident for the Z/h = 3.2 layer. Local advection took place during the afternoon resulting in an increase in the stability of the uppermost measured layer and propagated slowly downwards. The equilibrium layer was between Z/h ~ 1.5 to 2.4. The residuals were significantly different from zero for the uppermost layers Z/h = 2.7 and 3.2 during these periods. Our findings suggest that the depth and location of the internal equilibrium layer above trickle irrigated row crop fields surrounded by dry bare areas, vary in response to wind speed and the temperature of the soil in between the rows of the crop. For some time intervals, the computation of fluxes using the conventional flux-gradient approach measurements was not possible.

Climate extreme events (such as those associated to strong El Niño events) highly affect Mexican agriculture, since more than sixty percent of it is rainfed. The basic crop cultivated is maize, which is still the main source of nutrients for a large portion of the rural population in the country. Within the project Capacity Building for Stage II Adaptation to Climate Change in Central America, México and Cuba, we analyze the strategies developed by maize producers in the central region of the country to cope with climatic adverse events. Impact on rainfed maize due to climate variability and climate change conditions are studied using a crop simulation model. Several adaptation measures can be evaluated using that model. However, the effect of other stressors must be considered in an assessment of the adaptive capacity of small farmers to climate variability and change. Key stakeholders’ involvement in the region helped us to decide which of the adaptive measures could be viable under the current conditions and under future climatic conditions. The construction of greenhouses, the use of compost, and dripping irrigation, were some of the techniques selected with the participation of the stakeholders. The enthusiastic responses to these measures allow us to consider that they can prevail in the future, under climate change conditions. However, the adaptation to climate change includes –besides the stated techniques– the generation of the capacities to cope with climatic adverse events, that is, to enhance the adaptive capacities to climate change among the key stakeholders.

Meteorological data were recorded at eight stations located along the coast of the Pacific Ocean and three along the coast of the Gulf of California, aimed to assess the spatial influence of Santa Ana weather conditions in the Baja California Peninsula. February 2002 featured two Santa Ana events: one from the 9 to the 12 and another from the 21 to the 22. The first Santa Ana event had the strongest winds, however relative humidity and temperature behaved similarly on both events at some stations. Data from the Pacific Ocean showed typical Santa Ana condition patterns: wind speed and temperature increase opposed to decreased relative humidity values. Data from the Gulf of California did not show the typical temperature rise of a Santa Ana condition, but there was a decrease on the amplitude of the diurnal variability of air temperature and relative humidity as well as a marked increase on wind strength. Wind direction during the Santa Ana events on the Pacific side was NE and NW on the Gulf of California. NE winds are associated to the shift on the position of the North Pacific High Pressure Center, which moves towards the continent. Data suggest that relative humidity may be the best parameter to monitor both occurrence and length of Santa Ana conditions on the Pacific side. Normal weather conditions show a negative air-sea temperature difference, but during both Santa Ana events this difference was positive and higher than 10 ºC. Latent and sensible heat fluxes drastically increased during both events, reaching values more than three times higher than those for normal conditions, which is due to the presence of strong winds combined with a drier and hotter air mass over the ocean.

n this paper, Principal Component Analysis has been applied to investigate the spatial variability of errors in the INSAT derived quantitative precipitation estimates (QPE) over the Indian monsoon region, using daily rainfall analysis (at the same resolution) for the period from 1 June to 30 August of summer monsoon 2001. The study shows that the QPE errors have certain spatial variability. The orographic rainfall is significantly underestimated along the Western Ghats and along the foothills of the Himalayas, where the root mean square errors are also very large. Otherwise, the performance of the QPE is reasonably good over the rest of the region. The first principal component, which explains about 5.1% of the variance, corresponds to the onset phase of the monsoon during June, when strong positive loadings dominate over the southern parts of the country. The second principal component explaining about 4.2% of the variance, has strong positive loading in the intermittent presence of the monsoon low pressure system over the east central parts of the country. The third principal component which explains 3.3% of the variance is associated with the monsoon trough at the normal position, and the fourth principal component which explains 3.1% of the variance is associated with the monsoon trough at the southern position.

On 21 July 2001 several severe storms developed over the eastern region of Cuba in the afternoon hours and hail was observed. A numerical simulation was performed to study the structure and evolution of convection on that day with the aid of the 1800 UTC sounding. Furthermore, three more simulations were performed to study the effect of the vertical wind profile on the severity of the simulated storms. The Advanced Regional Prediction System model (ARPS) was used for this numerical study. An initial storm that later split into two new storms that moved to the right and to the left of the mean wind was simulated. The right-moving storm (RS) developed more than the left-moving one (LS). Hail was observed in most of the simulation time but the largest amount of hail reached the surface after the splitting in the RS. Two mechanisms were responsible for the inhibition of the LS. First, a vertical pressure gradient that acted against the main updraft development. Second, the entrainment of drier and colder air in the LS’s updraft at midlevels that came directly from the downdraft region. The wind shear above 10 km was favorable for a larger hail production, intensity and maximum values at the surface and a larger precipitation area. When the wind shear below 7 km was removed, the total volume of precipitation, the intensity of precipitation, maximum horizontal wind and maximum updraft were the largest compared to the other simulations. The LS was not inhibited in this case and both storms reached the same strength. The mechanisms that inhibited the development of the LS were not present in this simulation.

We have used the Thermodynamic Model of the Climate to estimate the effect of variations in the low cloud cover on the surface temperature of the Earth in the Northern Hemisphere during the period 1984-1994. We assume that the variations in the low cloud cover are proportional to the variation of the cosmic ray flux measured during the same period. The results indicate that the effect in the surface temperature is more significant in the continents, where for July of 1991, we have found anomalies of the order of 0.7 ºC for the southeastern of Asia and 0.5 ºC for the northeast of México. For an increase of 0.75% in the low cloud cover, the surface temperature computed by the model in the North Hemisphere presents a decrease of ~0.11 ºC; however, for a decrease of 0.90% in the low cloud cover, the model gives an increase in the surface temperature of ~0.15 ºC, these two cases correspond to a climate sensitivity factor of 0.14 ºC/Wm−2 , which is almost half of the climate sensitivity factor for the case of forcing by duplication of atmospheric CO2. These decreases or increases in surface temperature by increases or decreases in low clouds cover are ten times greater than the overall variability of the non-forced model time series.

The CRR (Convective Rainfall Rate) algorithm was developed to detect intense mesoscale convective cells and to screen the most probable precipitation associated. It estimates rainfall intensity using the three bands of the Meteosat-7 and matrices calibrated with earth-based radars. Calibration matrices were performed following an accurate version of the Rainsat techniques but combining the infrared bands to detect convective clouds. Matrices were developed, up for the North of Europe, over the Baltic countries, with data from the radar of the Baltex Project provided by the SMHI (Swedish Meteorological and Hydrological Institute) and for the South of Europe, over the Iberian Peninsula, with radar data as provided by the INM (Spanish Meteorological Institute). In the present research, the CRR calibration methodology is validated, an analysis of calibration matrices differences in both areas over Europe is detailed and CRR resulting images are verified in a qualitative manner using rainfall radar images as ground true.

We have analyzed 37 years of climate data to describe the behavior of the precipitation and its relation with temperature in coffee farm areas in the central part of the state of Veracruz, particularly in the municipalities of Coscomatepec and Huatusco. We analyze the tendencies of the annual averages of the precipitation. Monthly averages of the precipitation are related with monthly averages of the temperature as useful parameters to predict intense rains. Gamma distributions were adjusted to total monthly precipitation to approximate the probability of given intervals. Gumbel distributions were adjusted to daily extreme values for monthly intervals and to monthly extremes for annual intervals. The relation of the precipitation and the El Niño/Southern Oscillation (ENSO) phenomenon is analyzed. The influence of ENSO over the precipitation was found to be significant and translated as a reduction of the midsummer drought.

Cyclones and anticyclones are the dominant synoptic scale meteorological systems in midlatitudes. An attractive way to study dynamical aspects of these structures is provided by the use of potential vorticity (PV) framework. In this paper several aspects of midlatitude cyclogenesis are investigated within this PV framework using a case study analysis. The analysis of absolute, relative and potential vorticity implies the significance of the upper level dynamics in the initiation of this case of cyclogenesis. On one hand, the isobaric vorticity analysis appears to be informative, accurate and easy to use as a method for describing the upper-level dynamics. On the other hand the PV analysis provided a summarized picture of the development and the evolution at upper and lower levels, which is directly visible, on the basis of a smaller number of plots compared with the isobaric vorticity analysis. The display of the time sequence of the PV on the appropriate isentropic surface helped in easily understanding the dynamics of the three-dimensional upper level development.