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Held I.M.,National Oceanic and Atmospheric Administration | Winton M.,National Oceanic and Atmospheric Administration | Takahashi K.,Instituto Geofisico del Peru | Delworth T.,National Oceanic and Atmospheric Administration | And 2 more authors.
Journal of Climate | Year: 2010

The fast and slow components of global warming in a comprehensive climate model are isolated by examining the response to an instantaneous return to preindustrial forcing. The response is characterized by an initial fast exponential decay with an e-folding time smaller than 5 yr, leaving behind a remnant that evolves more slowly. The slow component is estimated to be small at present, as measured by the global mean near-surface air temperature, and, in the model examined, grows to 0.4°C by 2100 in the A1B scenario from the Special Report on Emissions Scenarios (SRES), and then to 1.4°C by 2300 if one holds radiative forcing fixed after 2100. The dominance of the fast component at present is supported by examining the response to an instantaneous doubling of CO2 and by the excellent fit to the model's ensemble mean twentieth-century evolution with a simple one-box model with no long times scales. © 2010 American Meteorological Society. Source

Chau J.L.,Instituto Geofisico del Peru | Goncharenko L.P.,Massachusetts Institute of Technology | Fejer B.G.,Utah State University | Liu H.-L.,High Altitude Observatory
Space Science Reviews | Year: 2012

There are several external sources of ionospheric forcing, including these are solar wind-magnetospheric processes and lower atmospheric winds and waves. In this work we review the observed ion-neutral coupling effects at equatorial and low latitudes during large meteorological events called sudden stratospheric warming (SSW). Research in this direction has been accelerated in recent years mainly due to: (1) extensive observing campaigns, and (2) solar minimum conditions. The former has been instrumental to capture the events before, during, and after the peak SSW temperatures and wind perturbations. The latter has permitted a reduced forcing contribution from solar wind-magnetospheric processes. The main ionospheric effects are clearly observed in the zonal electric fields (or vertical E×B drifts), total electron content, and electron and neutral densities. We include results from different ground- and satellite-based observations, covering different longitudes and years. We also present and discuss the modeling efforts that support most of the observations. Given that SSW can be forecasted with a few days in advance, there is potential for using the connection with the ionosphere for forecasting the occurrence and evolution of electrodynamic perturbations at low latitudes, and sometimes also mid latitudes, during arctic winter warmings. © 2011 Springer Science+Business Media B.V. Source

Takahashi K.,Instituto Geofisico del Peru
Geophysical Research Letters | Year: 2012

The diurnal cycle in the oceanic surface winds in the tropical eastern Pacific is shown, through numerical experiments with a regional atmospheric model, to be associated with the migrating diurnal atmospheric thermal tide, forced by absorption of solar near-IR radiation by tropospheric water vapor, and a topographically-modified extended sea-breeze, forced by diurnal land heating. Idealized experiments prove capable of discriminating the effects of both processes, showing that beyond 2000km from the coast, the thermal tide is dominant, while closer to the coast both processes are of the same order. The shortwave forcing due to water vapor is also found to produce a diurnal cycle in precipitation, but the process appears to be independent from the thermal tide and it is proposed that this effect is mediated by the radiatively-forced changes in the column stability. Copyright 2012 by the American Geophysical Union. Source

Takahashi K.,Instituto Geofisico del Peru | Dewitte B.,IRD LEGOS
Climate Dynamics | Year: 2016

It has been previously proposed that two El Niño (EN) regimes, strong and moderate, exist but the historical observational record is too short to establish this conclusively. Here, 1200 years of simulations with the GFDL CM2.1 model allowed us to demonstrate their existence in this model and, by showing that the relevant dynamics are also evident in observations, we present a stronger case for their existence in nature. In CM2.1, the robust bimodal probability distribution of equatorial Pacific sea surface temperature (SST) indices during EN peaks provides evidence for the existence of the regimes, which is also supported by a cluster analysis of these same indices. The observations agree with this distribution, with the EN of 1982–1983 and 1997–1998 corresponding to the strong EN regime and all the other observed EN to the moderate regime. The temporal evolution of various indices during the observed strong EN agrees very well with the events in CM2.1, providing further validation of this model as a proxy for nature. The two regimes differ strongly in the magnitude of the eastern Pacific warming but not much in the central Pacific. Observations and model agree in the existence of a finite positive threshold in the SST anomaly above which the zonal wind response to warming is strongly enhanced. Such nonlinearity in the Bjerknes feedback, which increases the growth rate of EN events if they reach sufficiently large amplitude, is very likely the essential mechanism that gives rise to the existence of the two EN regimes. Oceanic nonlinear advection does not appear essential for the onset of strong EN. The threshold nonlinearity could make the EN regimes very sensitive to stochastic forcing. Observations and model agree that the westerly wind stress anomaly in the central equatorial Pacific in late boreal summer has a substantial role determining the EN regime in the following winter and it is suggested that a stochastic component at this time was key for the development of the strong EN towards the end of 1982. © 2015, The Author(s). Source

Goncharenko L.P.,Massachusetts Institute of Technology | Coster A.J.,Massachusetts Institute of Technology | Chau J.L.,Instituto Geofisico del Peru | Valladares C.E.,Boston College
Journal of Geophysical Research: Space Physics | Year: 2010

We investigate the ionospheric response to several stratospheric sudden warming events which occurred in Northern Hemisphere winters of 2008 and 2009 during solar minimum conditions. We use GPS total electron content data in a broad latitudinal region at ±40° geographic latitude and a single longitude, 75°W. In all cases, we find a strong daytime ionospheric response to stratospheric sudden warmings. This response is characterized by a semidiurnal character, large amplitude, and persistence of perturbations for up to 3 weeks after the peak in high-latitude stratospheric temperatures. The ionospheric perturbations at the lower latitudes usually begin a few days after the peak in stratospheric temperature and are observed as an enhancement of the equatorial ionization anomaly (EIA) in the morning sector and a suppression of the EIA in the afternoon sector. There is also evidence of a secondary enhancement in the postsunset hours. Once observed in the low latitudes, the phase of semidiurnal perturbations progressively shifts to later local times in subsequent days. This progressive shift occurs at a different rate for different stratospheric warming events. The large magnitude and persistence of ionospheric perturbations, together with the predictability of stratospheric sudden warmings several days in advance, present an opportunity to investigate these phenomena in a systematic manner which may eventually lead to a multiday forecast of low-latitude ionosphere conditions. Copyright 2010 by the American Geophysical Union. Source

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