Variabilidad multidecadal del Atlántico norte en modelos del CMIP5

Ponencia presentada en: XXXII Jornadas Científicas de la AME y el XIII Encuentro Hispano Luso de Meteorología celebrado en Alcobendas (Madrid), del 28 al 30 de mayo de 2012.Este trabajo ha sido financiado gracias a los proyectos MICINN CGL2011-13564-E, CGL2009-10285 y MARM MOVAC 200800050084028

Southern hemisphere sensitivity to ENSO patterns and intensities: impacts over subtropical South America

El Niño flavors influence Subtropical South American (SSA) rainfall through the generation of one or two quasi-stationary Rossby waves. However, it is not yet clear whether the induced wave trains depend on the El Niño pattern and/or its intensity. To investigate this, we performed different sensitivity experiments using an Atmospheric General Circulation Model (AGCM) which was forced considering separately the Canonical and the El Niño Modoki patterns with sea surface temperature (SST) maximum anomalies of 1 and 3 ◦C. Experiments with 3 ◦C show that the Canonical El Niño induces two Rossby wave trains, a large one emanating from the western subtropical Pacific and a shorter one initiated over the central-eastern subtropical South Pacific. Only the shorter wave plays a role in generating negative outgoing longwave radiation (OLR) anomalies over SSA. On the other hand, 3 ◦C El Niño Modoki experiments show the generation of a large Rossby wave train that emanates from the subtropical western south Pacific and reaches South America (SA), promoting the development of negative OLR anomalies over SSA. Experiments with 1 ◦C show no impacts on OLR anomalies over SSA associated with El Niño Modoki. However, for the Canonical El Niño case there is a statistically significant reduction of the OLR anomalies over SSA related to the intensification of the upper level jet stream over the region. Finally, our model results suggest that SSA is more sensitive to the Canonical El Niño, although this result may be model dependent

Multidecadal Modulation of ENSO Teleconnection with Europe in Late Winter: Analysis of CMIP5 Models

Many studies point to a robust ENSO signature on the North Atlantic–European (NAE) sector associated with a downstream effect of Rossby wave trains. Some of these works also address a nonstationary behavior of the aforementioned link, but only few have explored the possible modulating factors. In this study the internal causes within the ocean–atmosphere coupled system influencing the tropospheric ENSO–Euro-Mediterranean rainfall teleconnection have been analyzed. To this aim, unforced long-term preindustrial control simulations from 18 different CMIP5 models have been used. A nonstationary impact of ENSO on Euro-Mediterranean rainfall, being spatially consistent with the observational one, is found. This variable feature is explained by a changing ENSO-related Rossby wave propagation from the tropical Pacific to the NAE sector, which, in turn, is modulated by multidecadal variability of the climatological jet streams associated with the underlying sea surface temperature (SST). The results, therefore, indicate a modulation of the ENSO–Euro-Mediterranean rainfall teleconnection by the internal (and multidecadal) variability of the ocean–atmosphere coupled system.This study was supported by the European project PREFACE (603521), and the Spanish projects TRACS (CGL2009-10285) and MULCLIVAR (CGL2012- 38923-C02-01).Peer reviewe

Statistical-observational analysis of skillful oceanic predictors of heavy daily precipitation events in the Sahel

In this paper, the sea surface temperature (SST) based statistical seasonal forecast model (S4CAST) is utilized to examine the spatial and temporal prediction skill of Sahel heavy and extreme daily precipitation events. As in previous studies, S4CAST points out the Mediterranean Sea and El Niño Southern Oscillation (ENSO) as the main drivers of Sahel heavy/extreme daily rainfall variability at interannual timescales (period 1982–2015). Overall, the Mediterranean Sea emerges as a seasonal short-term predictor of heavy daily rainfall (1 month in advance), while ENSO returns a longer forecast window (up to 3 months in advance). Regarding the spatial skill, the response of heavy daily rainfall to the Mediterranean SST forcing is significant over a widespread area of the Sahel. Contrastingly, with the ENSO forcing, the response is only significant over the southernmost Sahel area. These differences can be attributed to the distinct physical mechanisms mediating the analyzed SST-rainfall teleconnections. This paper provides fundamental elements to develop an operational statistical-seasonal forecasting system of Sahel heavy and extreme daily precipitation events

Multidecadal modulation of ENSO teleconnection with Europe in late 2 winter: analysis of CMIP5 models

Many studies point to a robust ENSO signature on the North Atlantic-European (NAE) sector associated with a downstream effect of Rossby wave trains. Some of these works also address a nonstationary behavior of the aforementioned link, but only few have explored the possible modulating factors. In this study the internal causes within the ocean-atmosphere coupled system influencing the tropospheric ENSO-Euro-Mediterranean rainfall teleconnection have been analyzed. To this aim, unforced long-term preindustrial control simulations from 18 different CMIP5 models have been used. A nonstationary impact of ENSO on Euro-Mediterranean rainfall, being spatially consistent with the observational one, is found. This variable feature is explained by a changing ENSO- elated Rossby wave propagation from the tropical Pacific to the NAE sector, which, in turn, is modulated by multidecadal variability of the climatological jet streams associated with the underlying sea surface temperature (SST). The results, therefore, indicate a modulation of the ENSO-Euro-Mediterranean rainfall teleconnection by the internal (and multidecadal) variability of the ocean-atmosphere coupled system

Influence of decadal sea surface temperature variability on northern Brazil rainfall in CMIP5 simulations

The Amazonia and Northeast regions of northern Brazil are characterized by very different rainfall regimes but have certain similarities in terms of their variability. The precipitation variability in both regions is strongly linked to the tropical Atlantic sea surface temperature (SST) gradient and the tropical Pacific SST anomalies, which at decadal timescales are modulated by the Atlantic Multidecadal Variability (AMV) and the Interdecadal Pacific Oscillation (IPO) modes of SST, respectively. On the other hand, it has been found that state-of-the-art models from the fifth phase of the Coupled Model Intercomparison Project (CMIP5) are able to reproduce some of the characteristics of the low-frequency SST variability modes. In this work we analyze how CMIP5 models simulate the observed response of precipitation in the Amazonia and Northeast regions to the AMV and the IPO and the atmospheric mechanisms involved. Results show that, in both CMIP5 simulations and observations, Amazonia and Northeast rainfall response to the AMV is the opposite, due to the modulation of the intertropical convergence zone (ITCZ) position. Conversely, the IPO affects equally both regions as a consequence of anomalous subsidence over the entire northern Brazil triggered by warm SST anomalies in the tropical Pacific. Such results suggest that an improvement of the predictability of decadal SST modes will directly revert into a better prediction of changes in the Amazonia and Northeast rainfall at longer timescales

Predicción estacional de las lluvias en África Occidental bajo un modelo estadístico de predictores no estacionarios

Ponencia presentada en: XXXII Jornadas Científicas de la AME y el XIII Encuentro Hispano Luso de Meteorología celebrado en Alcobendas (Madrid), del 28 al 30 de mayo de 2012.El estudio de los impactos derivados de la variabilidad climática tropical ha adquirido cada vez más importancia durante las últimas décadas, ya sea a escala regional o global. En este sentido, existen modelos estadísticos y dinámicos enfocados en el estudio de las anomalías estacionales de precipitación relativas al Monzón de África Occidental (MAO).Este trabajo ha sido posible gracias a la financiación proporcionada por los proyectos CGL2009-10285 y V.R. 101/11: CREACIÓN Y DONACIÓN DE UN MODELO ESTADÍSTICO DE PREDICCIÓN DE LLUVIAS EN EL SAHE

Atlantic control of the late nineteenth-century Sahel humid period

Precipitation regime shifts in the Sahel region have dramatic humanitarian and economic consequences such as the severe droughts during the 1970s and 1980s. Though Sahel precipitation changes during the late twentieth century have been extensively studied, little is known about the decadal variability prior to the twentieth century. Some evidence suggests that during the second half of the nineteenth century, the Sahel was as rainy as or even more rainy than during the 1950s and 1960s. Here, we reproduce such an anomalous Sahel humid period in the late nineteenth century by means of climate simulations. We show that this increase of rainfall was associated with an anomalous supply of humidity and higher-than-normal deep convection in the mid- and high troposphere. We present evidence suggesting that sea surface temperatures (SSTs) in the Atlantic basin played the dominant role in driving decadal Sahel rainfall variability during this early period

Impact of the Madden Julian Oscillation on the summer West African monsoon in AMIP simulations

At intraseasonal timescales, convection over West Africa is modulated by the Madden Julian Oscillation (MJO). In this work we investigate the simulation of such relationship by 11 state-of-the-art atmospheric general circulation models runs with prescribed observed sea surface temperatures. In general, the Atmospheric Model Intercomparison Project simulations show good skill in capturing the main characteristics of the summer MJO as well as its influence on convection and rainfall over West Africa. Most models simulate an eastward spatiotemporal propagation of enhanced and suppressed convection similar to the observed MJO, although their signal over West Africa is weaker in some models. In addition, the ensemble average of models' composites gives a better performance in reproducing the main features and timing of the MJO and its impact over West Africa. The influence on rainfall is well captured in both Sahel and Guinea regions thereby adequately producing the transition between positive and negative rainfall anomalies through the different phases as in the observations. Furthermore, the results show that a strong active convection phase is clearly associated with a stronger African Easterly Jet (AEJ) but the weak convective phase is associated with a much weaker AEJ. Our analysis of the equatorial waves suggests that the main impact over West Africa is established by the propagation of low-frequency waves within the MJO and Rossby spectral peaks. Results from the simulations confirm that it may be possible to predict anomalous convection over West Africa with a time lead of 15-20 day

SiGOG: simulated GPS observation generator

For many applications, access to unbiased or error-controlled global positioning system (GPS) observations can be very useful. This paper is devoted to the description of simulated GPS observations generator (SiGOG), a software that simulates GPS observations. It presents the results of tests of SiGOG accuracy using GPS processing software, and demonstrates its successful performance as a differential GPS (DGPS) correction provider.Facultad de Ciencias Astronómicas y Geofísica