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El verano de 2004 fue un clarinazo de alarma: cuatro huracanes descomunales arrasaron Florida y diez tifones azotaron las tierras de Japon, cuatro mas que los padecidos en el ano anterior. Los cientificos, asombrados, no se ponian de acuerdo en la explicacion del fenomeno, especialmente en cuanto al papel del calentamiento global en tan inusitado aumento. Despues vino la estacion de 2005, que batio marcas en el Atlantico Norte con los devastadores huracanes Katrina y Rita. Pero en 2006, tras un fuerte aumento de las primas de seguro en el sudeste de EE.UU., el numero de tormentas fue bastante menor de lo previsto. Si el calentamiento global era determinante, ?por que este subito descenso? El estudio minucioso de las pautas del clima esta alcanzando una explicacion consensuada de los crecimientos espectaculares de 2004 y 2005, asi como del apaciguado 2006. Por desgracia, pronostica tambien problemas meteorologicos a largo plazo.
Studies of the interannual variability of the 500 mb flow in the Southern Hemisphere for 1972–78 have revealed 1) a quasi-biennial fluctuation in the zonal mean geopotential height and westerly wind fields where there is a systematic poleward progression of anomalies, and 2) a longer period fluctuation, primarily in Wave 1, which has been identified with the Southern Oscillation. These phenomena are further studied regionally by considering four 90° sectors. Results show the dominant contributions to the fluctuations in the zonal mean fields come from the Australasian and South Pacific sectors. Only in the Australasian region is the quasi-biennial poleward progression of anomalies strongly evident. The South Pacific is dominated by lower frequency fluctuations associated with the Southern Oscillation. However, the sequences in all four sectors are correlated with those in the zonal mean fields. When the flow is stronger than normal in mid-latitudes it tends to be weaker than normal in low and high latitudes, and vice versa, in all sectors and in the zonal mean.
Climate change is likely to be manifested on societies around the world mainly through changes in extremes. As a result, the scientific community faces an increasing demand for regularly updated appraisals of evolving climate conditions and extreme weather. Such information would be immensely beneficial for adaptation planning. A group of climate scientists representing the United Kingdom, the United States, Australia, Canada, and South Africa assembled on 26 January 2009 at the National Center for Atmospheric Research (NCAR), in Colorado, to discuss how to meet this challenge. This first meeting of the International Group on Attribution of Climate‐Related Events (ACE) was sponsored by the Science and Innovation Network of the U.K. Foreign and Commonwealth Office (FCO) and NCAR and was organized in collaboration with the U.S. National Oceanic and Atmospheric Administration (NOAA), the Met Office Hadley Centre, and the University of Oxford.
Projections of future climate change depend largely on the results of computer models. Such models are becoming increasingly sophisticated, but they do not offer the certainties that policy-makers would like.
Global Earth’s Energy Imbalance (EEI) is a fundamental metric of climate change, and the local distribution of the imbalance has implications for regional climate variations. It has been a major challenge to rein in the uncertainties and reasonably establish the EEI. Previous chapters have exploited the local energy imbalance estimates to examine resulting heat transports and anomalies, and teleconnections. The atmosphere and oceans are dynamically active, and many phenomena attempt to move heat to where it can best be either lost in some sense, such as by radiation to space, or perhaps sequestered by being buried deep in the ocean. Although there is somewhat constrained effectiveness in many phenomena, such as hurricanes or ENSO, in redistributing heat and keeping regions cooler than they otherwise would be, these aspects are often not replicated well in climate models. Hence it is vital to understand the net heat gain, and how much and where heat is distributed within the Earth system. How much heat might be readily purged and serve as a negative feedback to warming?
Comprehensive diagnostic comparisons and evaluations have been carried out with the National Centers for Environmental Prediction/National Center for Atmos
The IPCC (Intergovernmental Panel on Climate Change) is a primary user of studies of the ocean and how it is changing.Following an introduction to the IPCC, the role of the ocean in climate is outlined, and the main findings from the 2007 IPCC assessment are described, along with outstanding issues for ocean science.The progress in addressing these issues is briefly discussed along with some recommendations for ocean observations.
The Sun is the center of our climate system. It provides a fairly steady stream of radiant energy to Earth, and in order to keep from heating up, Earth in turn radiates energy back out into space. In between the incoming and outgoing radiation are all of the rich complex processes involved in the climate system including all of the weather systems, the entire hydrological cycle, the ocean, land and ice, and the multitude of forms of heat and energy on the planet. The internal interactive components in the climate system (Fig. 1.1) include the atmosphere, oceans, ice, and land.
No abstract is provided for this article.
No abstract is provided for this article.
No abstract is provided for this article.
An analysis of the spring–summer 1988 drought and 1993 floods over North America reveals a reversal in the sign of anomalies in several fields. Large sea surface temperature anomalies of opposite signs existed in the tropical Pacific with strong La Niña conditions in 1988 and a mature El Niño in 1993. The distribution of tropical convection in the convergence zones and associated latent heating of the atmosphere were correspondingly altered, implying a large-scale switch in the anomalous tropical heating and forcing of extratropical quasi-stationary waves in the atmosphere, influencing the subtropical jet stream over the North Pacific and across North America. In 1988 the jet stream and the closely related storm track of high-frequency disturbances in the upper troposphere were displaced into Canada well north of the normal location—the farthest north of any year from 1979 to 1993. In 1993 a broader jet stream and the storm track were displaced well south of normal to a more springlike location across the United States—the farthest south by over 200 km of any year from 1979 to 1993. High-frequency eddy activity in the Pacific-North American storm track is shown to reinforce the anomalous jet streams in both years. An analysis of the moisture budgets reveals a stronger river of atmospheric moisture flowing across the Gulf of Mexico into the central and eastern United States in 1993. Also, in the lower atmosphere, the storm track in 1993 was more active, and its lower latitude allowed the cyclonic disturbances to tap into the moisture source, transport moisture into the upper Mississippi River basin, and precipitate it out. It is deduced that local evaporation may have enhanced the precipitation and helped perpetuate and prolong the conditions. In contrast, in 1988 disturbances were weaker and displaced far enough north to avoid most of the moisture source, and the drought was perpetuated by the dry conditions. Consequently, these effects should be viewed as feedbacks that amplify and prolong the response, while from the standpoint of the atmosphere, the anomalous tropical Pacific sea surface temperatures are a notable (but not the sole) external forcing of the patterns.
The hydrological cycle fundamentally involves evaporation (E) of moisture from the land and vegetation or ocean surface into the atmosphere, and back again as precipitation (P) (Fig. 10.1). Evaporation produces evaporative cooling at the surface and moistens the air. It includes transpiration from plants in which water enters the atmosphere through the tiny stomata in leaves as photosynthesis occurs. Together these are called evapotranspiration. Precipitation and the relationships to humidity and sea surface temperatures (SSTs) were introduced in Section 5.4. Water vapor is moved around by the atmosphere, and the precipitation occurs elsewhere, often in preferred locations such as mid-latitude storm tracks or tropical monsoons and convergence zones.
A detailed vertically integrated atmospheric heat and energy budget is presented along with estimated heat budgets at the surface and top-of-atmosphere for the subtropics. It is shown that the total energy transports are remarkably seamless in spite of greatly varying mechanisms. From the Tropics to about 31° latitude, the primary transport mechanisms are the Hadley and Walker overturning circulations. In the extratropics the energy transports are carried out by baroclinic eddies broadly organized into storm tracks and quasi-stationary waves that covary in a symbiotic way as the location and activity in storm tracks are determined by, and in turn help maintain through eddy transports, the quasi-stationary flow. In the upward branch of the Hadley cell, the predominant diabatic process is latent heating that results from convergence of moisture by the circulation itself. Hence large poleward transports of dry static energy are compensated by equatorward transports of latent energy, resulting in a modest poleward transport of moist static energy. The subsidence warming in the downward branch is compensated by cooling in the subtropics that mainly arises from energy transport to higher latitudes by transient baroclinic eddies that are stronger in the winter hemisphere. Effectively, the outgoing longwave radiation to space is distributed over middle and high latitudes and is not limited to the clear dry regions in the subtropics. Further, some of the radiative cooling in the subtropics is a consequence of the circulation. Hence the cooling by transient eddies in the subtropics is a fundamental driver of the observed Hadley circulation and realizes the seamless transport from Tropics to extratropics, while tropical sea surface temperatures over the oceans determine where the upward branch is located. The relatively clear skies in the subtropics further provide for ample absorption of solar radiation at the surface where it feeds strong evaporation, which exceeds precipitation, and supplies the equatorward flow of latent energy into the upward branch of the Hadley circulation as well as the poleward transports into midlatitude storm tracks. The evaporation is sufficiently strong that it is also compensated by a subsurface ocean heat transport that in turn is driven by the Hadley circulation surface winds.
