519 publications from this institution
Two global data sets have been analyzed to determine the interannual variability of the zonal mean mass distribution. The first is a National Meteorological Center (NMC) global data set of sea level pressures beginning in December 1977 and surface pressures beginning in April 1979. The second is an 11‐year (1972–1982) hybrid set of sea level pressures from the Australian southern hemisphere and U.S. Navy northern hemisphere analyses. The two sets are compared and evaluated by seeing how well they satisfy the constraint of conservation of mass. Anomalies in total mass due to changes in water vapor content of the atmosphere are lost in the data problems. Several inhomogeneities or discontinuities are found and are identified either with changes in analysis procedures in both data sets or the introduction of new orography and operational models at NMC. Consequently only limited periods of data are suitable for determining the dominant modes of variability. Nevertheless, hemispheric mean anomalies in mass in one hemisphere tend to be mirrored in the other, and it is clear that previously deduced fluctuations in hemispheric mean mass are mostly real. Predominant modes of variability of zonal means reveal systematic exchanges of mass (1) almost entirely confined within each hemisphere in isolation, (2) between the extratropics of each hemisphere with little impact on the tropics as an antisymmetric mode, and (3) between the tropics and extratropics in a symmetric mode. The second mode played a strong role in redistributing mass during April–July of 1979 during the First GARP Global Experiment (FGGE) and resulted in an exceptionally deep circumpolar trough over the southern hemisphere and record high pressures over the northern hemisphere. The possible origin of these modes is briefly considered.
The effects of the inclusion of a Helmholtz term in a quasi-geostrophic model, formulated as part of a lower boundary condition, are investigated using a two-layer model. The Helmholtz term has two main effects, both of which appear desirable in a quasi-geostrophic model. As well as reducing the phase speed of all waves, and thereby controlling the otherwise large retrograde motion of ultra-long Rossby waves, it reduces growth rates of unstable waves. The Helmholtz term reduces the westward slope with height of unstable waves, more so for shorter wave lengths.The Helmholtz term is shown to be important for all quasi-geostrophic models. However, its use with an enhanced factor of about 10, although desirable for “best” forecasts, has little physical basis and merely serves to offset shortcomings of the model.
No abstract is provided for this article.
The problem of global warming arises from the buildup of greenhouse gases such as carbon dioxide from burning of fossil fuels and other human activities that change the composition of the atmosphere and alter outgoing longwave radiation (OLR). One geoengineering solution being proposed is to reduce the incoming sunshine by emulating a volcanic eruption. In between the incoming solar radiation and the OLR is the entire weather and climate system and the hydrological cycle. The precipitation and streamflow records from 1950 to 2004 are examined for the effects of volcanic eruptions from El Chichón in March 1982 and Pinatubo in June 1991, taking into account changes from El Niño‐Southern Oscillation. Following the eruption of Mount Pinatubo in June 1991 there was a substantial decrease in precipitation over land and a record decrease in runoff and river discharge into the ocean from October 1991–September 1992. The results suggest that major adverse effects, including drought, could arise from geoengineering solutions.
The state of knowledge and outstanding challenges and opportunities in global water cycle observations, research and modeling are briefly reviewed to set t
The Issues and Events report on the viability of geoengineering to counter global warming did not address the ethical issue. I use the following fable to illustrate the point.Once upon a time in an idyllic country, near a small town and a farming community, a rope hung out of the sky. One pull on the rope changed the weather from fine and sunny to cloudy and rainy, and the next pull changed it back. For many years the people cooperated; the farmers used the rains to help grow crops, and the townspeople enjoyed the sunny periods. But there came a time when the townspeople protested the rain and wanted more sunshine. The farmers were concerned about their crops. And so arguments broke out, with a person from the town pulling on the rope, followed quickly by a farmer pulling it again, and they pulled and pulled and … broke the rope.Given that the climate is changing because of inadvertent consequences of human activities, the question arises as to whether efforts should be made to deliberately change climate to counteract the warming. Aside from the wisdom and ability to do such a thing economically, the more basic question is the ethical one of who controls the rope. Who makes the decision on behalf of all humanity and other residents of planet Earth to change the climate deliberately? Climate change is not necessarily bad. The climate has always varied to some degree, and changes have occurred over decades and millennia. Humans and other creatures have adapted to the changes or perished; it is a part of evolution. Changes projected with increased greenhouse gases in the atmosphere may have some aspects that could be regarded as bad; increased heat waves and wildfires in summer, increased and more intense droughts, heavier rains and risk of flooding, stronger storms, decreases in air quality, and increases in bugs and disease are all likely threats. But in some areas, climates improve, high-latitude continents become more equable, growing seasons are longer, and so on. There are winners and losers. And it is possible to adapt to such changes—at least if the changes occur slowly enough. In other words, key issues are the rate and duration of change, perhaps more so than the nature of the new climate. In that sense, it is the disruptive part of climate change that might be argued as being bad.Given that climate change is not universally condemned, how can anyone justify deliberately acting to change the climate to benefit any particular group, perhaps even a majority? The ethical questions associated with climate manipulation loom so large that some forms of geoengineering are simply unacceptable. The forms that are acceptable include those that reduce emissions and mitigate the rates of change or reduce the amount of carbon dioxide in the atmosphere. Forms that propose to block sunlight in some fashion, perhaps to emulate a volcanic eruption, would change the hydrological cycle and weather patterns in ways that would be simply unacceptable, even if they were doable. The cost and viability of any such proposals are other major issues, but in my view, they are overwhelmed by the ethical considerations.© 2009 American Institute of Physics.
No abstract is provided for this article.
Recent studies have produced conflicting results about the impacts of climate change on drought. In this Perspective, a commonly used drought index and observational data are examined to identify the cause of these discrepancies. The authors indicate that improvements in the quality and coverage of precipitation data and quantification of natural variability are necessary to provide a better understanding of how drought is changing. Several recently published studies have produced apparently conflicting results of how drought is changing under climate change. The reason is thought to lie in the formulation of the Palmer Drought Severity Index (PDSI) and the data sets used to determine the evapotranspiration component. Here, we make an assessment of the issues with the PDSI in which several other sources of discrepancy emerge, not least how precipitation has changed and is analysed. As well as an improvement in the precipitation data available, accurate attribution of the causes of drought requires accounting for natural variability, especially El Niño/Southern Oscillation effects, owing to the predilection for wetter land during La Niña events. Increased heating from global warming may not cause droughts but it is expected that when droughts occur they are likely to set in quicker and be more intense.
No abstract is provided for this article.
The mean and annual cycle of energy flowing into the climate system and its storage, release, and transport in the atmosphere, ocean, and land surface are estimated with recent observations. An emphasis is placed on establishing internally consistent quantitative estimates with discussion and assessment of uncertainty. At the top of the atmosphere (TOA), adjusted radiances from the Earth Radiation Budget Experiment (ERBE) and Clouds and the Earth’s Radiant Energy System (CERES) are used, while in the atmosphere the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis and 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) estimates are used. The net upward surface flux (FS) over ocean is derived as the residual of the TOA and atmospheric energy budgets, and is compared with direct calculations of ocean heat content (OE) and its tendency (δOE/δt) from several ocean temperature datasets. Over land, FS from a stand-alone simulation of the Community Land Model forced by observed fields is used. A depiction of the full energy budget based on ERBE fluxes from 1985 to 1989 and CERES fluxes from 2000 to 2004 is constructed that matches estimates of the global, global ocean, and global land imbalances. In addition, the annual cycle of the energy budget during both periods is examined and compared with ocean heat content changes. The near balance between the net TOA radiation (RT) and FS over ocean and thus with OE, and between RT and atmospheric total energy divergence over land, are documented both in the mean and for the annual cycle. However, there is an annual mean transport of energy by the atmosphere from ocean to land regions of 2.2 ± 0.1 PW (1 PW = 1015 W) primarily in the northern winter when the transport exceeds 5 PW. The global albedo is dominated by a semiannual cycle over the oceans, but combines with the large annual cycle in solar insolation to produce a peak in absorbed solar and net radiation in February, somewhat after the perihelion, and with the net radiation 4.3 PW higher than the annual mean, as it is enhanced by the annual cycle of outgoing longwave radiation that is dominated by land regions. In situ estimates of the annual variation of OE are found to be unrealistically large. Challenges in diagnosing the interannual variability in the energy budget and its relationship to climate change are identified in the context of the episodic and inconsistent nature of the observations.
No abstract is provided for this article.
There is compelling evidence that the climate is changing, for whatever reason. We discuss the degree, nature, and cause of the climate variations and whether there is in fact a change, but the only way to resolve the issue is with solid information. This requires improved global observations of the state variables and the variables causing change (the forcings), the means to process these and understand them, and the ability to set them in a coherent physical (as well as chemical and biological) framework with models for diagnostic and prognostic purposes. Meanwhile, the information that helps settle these arguments and reduces uncertainties is also extremely valuable for many other purposes, including a myriad of practical applications for business, industry, government, and the general public. The following is a list of strategic requirements necessary for a comprehensive climate observing system: Climate observations from both space-based and in situ platforms are taken in ways that address climate needs and adhere to the 10 principles outlined by the NRC. The international framework for sharing data is vital. A global telecommunications and satellite ground systems network and satellite data telemetry capacity to enable data and products from all observing platforms to be disseminated. A climate observations analysis and tracking capability that produces global and regional analyses of various products for the atmosphere, oceans, land surface and hydrology, and the cryosphere. Four-dimensional data assimilation and reanalysis capabilities that process the multivariate data in a physically consistent framework to enable production of the analyses, not just for the atmosphere, but also for the oceans, land surface, and cryosphere. Global climate models that encompass all parts of the climate system and that are utilized in data assimilation and in making ensemble predictions originating from the initial observed state. A climate observation oversight and observing system monitoring capability that tracks the performance of the observations, the gathering of the data, and the processing systems. This must also include the resources and influence to fix problems and the capability to communicate climate requirements when observational systems are being discussed and established, such as for weather purposes or in establishing requirements for instruments on satellites. Although much has been learned about climate from past and present observing systems, we do not have an adequate climate observing system at present. Instead, we make do with an eclectic mix of observations mostly taken for other purposes. Nor are they adequately synthesized. Hence, in addition to making new observations, there is a strong rationale for building the system, and incorporating the management principles described here.
