Farneti R.,Princeton University |
Delworth T.L.,Noaa Geophysical Fluid Dynamics Laboratory
Journal of Physical Oceanography | Year: 2010
It has been suggested that a strengthening of the Southern Hemisphere winds would induce a more vigorous overturning through an increased northward Ekman flux, bringing more light waters into the oceanic basins and enhancing the upwelling of North Atlantic Deep Water in the Southern Ocean, thereby increasing ocean ventilation. Simulations from a coarse- and a fine-resolution version of a coupled model, subject to idealized wind stress changes in the Southern Ocean, are presented. In the fine-resolution eddy-permitting model, changes in poleward eddy fluxes largely compensate for the enhanced equatorward Ekman transport in the Southern Ocean. As a consequence, northward transport of light waters, pycnocline depth, Northern Hemisphere overturning, and Southern Ocean upwelling anomalies are much reduced compared with simulations in the coarse-resolution model with parameterized eddies. These results suggest a relatively weak sensitivity of present-day global ocean overturning circulation to the projected strengthening of the Southern Hemisphere winds. © 2010 American Meteorological Society.
Landsea C.W.,Noaa Nws National Hurricane Center |
Vecchi G.A.,Noaa Geophysical Fluid Dynamics Laboratory |
Bengtsson L.,University of Reading |
Knutson T.R.,Noaa Geophysical Fluid Dynamics Laboratory
Journal of Climate | Year: 2010
Records of Atlantic basin tropical cyclones (TCs) since the late nineteenth century indicate a very large upward trend in storm frequency. This increase in documented TCs has been previously interpreted as resulting from anthropogenic climate change. However, improvements in observing and recording practices provide an alternative interpretation for these changes: recent studies suggest that the number of potentially missed TCs is sufficient to explain a large part of the recorded increase in TC counts. This study explores the influence of another factor-TC duration-on observed changes inTCfrequency, using a widely used Atlantic hurricane database (HURDAT). It is found that the occurrence of short-lived storms (duration of 2 days or less) in the database has increased dramatically, from less than one per year in the late nineteenth-early twentieth century to about five per year since about 2000, while medium to long-lived storms have increased little, if at all. Thus, the previously documented increase in totalTCfrequency since the late nineteenth century in the database is primarily due to an increase in very short-lived TCs. The authors also undertake a sampling study based upon the distribution of ship observations, which provides quantitative estimates of the frequency of missed TCs, focusing just on the moderate to long-lived systems with durations exceeding 2 days in the raw HURDAT. Upon adding the estimated numbers of missed TCs, the time series of moderate to long-lived Atlantic TCs show substantial multidecadal variability, but neither time series exhibits a significant trend since the late nineteenth century, with a nominal decrease in the adjusted time series. Thus, to understand the source of the century-scale increase in Atlantic TC counts in HURDAT, one must explain the relatively monotonic increase in very short-duration storms since the late nineteenth century. While it is possible that the recorded increase in short-durationTCs represents a real climate signal, the authors consider that it is more plausible that the increase arises primarily from improvements in the quantity and quality of observations, along with enhanced interpretation techniques. These have allowed National Hurricane Center forecasters to better monitor and detect initial TC formation, and thus incorporate increasing numbers of very short-lived systems into the TC database. © 2010 American Meteorological Society.
Kunkel K.E.,North Carolina State University |
Karl T.R.,Noaa National Climatic Data Center |
Brooks H.,Noaa National Severe Storms Laboratory |
Kossin J.,Noaa National Climatic Data Center |
And 21 more authors.
Bulletin of the American Meteorological Society | Year: 2013
Review of the climate science for severe convective storms, extreme precipitation, hurricanes and typhoons, and severe snowstorms and ice storms in the US shows that the ability to detect and attribute trends varies, depending on the phenomenon. A specific subset of extreme weather and climate types affecting the country is discussed to examine these extreme weather conditions. The categories of storms described were selected as they caused property damage and loss of life. The identification of an extreme occurrence was based on meteorological properties in place of the destructiveness. The primary purpose was to examine the scientific evidence for the prevailing capability to detect trends and understand their causes for certain weather types, including severe convective storms and hurricanes and typhoons.