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  • 1
    Digitale Medien
    Digitale Medien
    An assessment of measures of storminess: simulated changes in northern hemisphere winter due to increasing C02 (1996)
    Springer
    Climate dynamics 12 (1996), S. 475-496 
    Details
    ISSN: 1432-0894
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract A range of diagnostics from two GCM simulations, one of the present-day climate and one of the last glacial maximum (LGM) is used to gain insight into their different temperature structures and eddy dynamics. There are large local increases in baroclinicity at the LGM, especially in the Atlantic storm track, with large accompanying increases in the low level transient eddy heat flux. However, the differences in the zonal mean are much smaller, and the increases in both baroclinicity and heat flux are confined to low levels. Supplementary experiments with baroclinic wave lifecycles confirm the marked contrast between local and zonal mean behaviour, but do not adequately explain the differences between the zonal mean climates. The total flux of energy across latitude circles in the Northern Hemisphere does not change much during DJF, although its transient component is actually reduced at the LGM (during JJA the transient component is increased). Calculations of total linear eddy diffusivity reveal that changes in the time mean stationary waves are chiefly responsible for the seasonal range of this quantity at the LGM, while they only account for half the seasonal range at the present-day.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02346820
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    An assessment of measures of storminess: simulated changes in northern hemisphere winter due to increasing CO2 (1996)
    Springer
    Climate dynamics 12 (1996), S. 467-476 
    Details
    ISSN: 1432-0894
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract. Two methods for identifying mid-latitude synoptic time scale variability have been applied to data from the first United Kingdom Meteorological Office (UKMO) coupled ocean-atmosphere model experiments with present day and gradually increasing CO2 concentrations. In the first the standard deviation of the time filtered mean sea level pressure field is taken to identify the location of the storm track and in the second individual cyclones are identified using synoptic criteria. The results have been compared with data from a 10 year archive of UKMO analysis. In the enhanced CO2 experiment the changes in storminess identified by the two methods have been compared with changes in mean and maximum winds with special emphasis on the North Atlantic. The relative utility of the different measures for predicting potentially damaging synoptic events is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003820050121
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Changes in mid-latitude variability due to increasing greenhouse gases and sulphate aerosols (1998)
    Springer
    Climate dynamics 14 (1998), S. 369-383 
    Details
    ISSN: 1432-0894
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract  Intra-seasonal variability in the Northern Hemisphere winter is investigated in ensembles of experiments using the Hadley Centre coupled ocean-atmosphere model. Synoptic techniques which identify low centres and blocking anticyclones have been used in preference to time-filtered variances of geopotential height as these may not uniquely identify true synoptic systems. Changes in mid-latitude variability are qualitatively similar in experiments that include changes in greenhouse gases only and those that also include the direct effects of sulphate aerosols. The presence of aerosols reduces the warming of the northern continents but the relatively larger warming of the land compared to the oceans remains in both experiments and at higher latitudes this leads to a reduced poleward transient flux of energy. There is an increase in the transient flux of energy at most latitudes, due to a greater transport of latent heat arising from the greater moisture availability. The total number of Northern Hemisphere storms decreases but there is a tendency towards deeper low centres. There are fewer storms in the North Pacific and North Atlantic source regions where the local baroclinicity is reduced. The climatological tracks from these regions are shorter with decreases at the northeastern ends of the tracks and increases in the regions with maximum counts towards the centre of the ocean basins. These changes are not generally statistically significant. The greatest changes in blocking anticyclones occur in the North Pacific where there is a downstream shift in the region of maximum activity. Changes in stationary waves show a strong increase in the PNA oscillation which may be influencing the changes in blocking as has been found by other authors. Possible mechanisms for forcing this response are speculated but it will need further experiments to unravel them.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003820050229
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  • 4
    Digitale Medien
    Digitale Medien
    An assessment of measures of storminess: Simulated changes in northern hemisphere winter due to increasing CO2 (1996)
    Springer
    Climate dynamics 12 (1996), S. 467-474 
    Details
    ISSN: 1432-0894
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract Two methods for identifying mid-latitude synoptic time scale variability have been applied to data from the first United Kingdom Meteorological Office (UKMO) coupled ocean-atmosphere model experiments with present day and gradually increasing CO2 concentrations. In the first the standard deviation of the time filtered mean sea level pressure field is taken to identify the location of the storm track and in the second individual cyclones are identified using synoptic criteria. The results have been compared with data from a 10 year archive of UKMO analysis. In the enhanced CO2 experiment the changes in storminess identified by the two methods have been compared with changes in mean and maximum winds with special emphasis on the North Atlantic. The relative utility of the different measures for predicting potentially damaging synoptic events is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02346819
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  • 5
    Digitale Medien
    Digitale Medien
    The second Hadley Centre coupled ocean-atmosphere GCM: model description, spinup and validation (1997)
    Springer
    Climate dynamics 13 (1997), S. 103-134 
    Details
    ISSN: 1432-0894
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract.  This study describes a new coupled ocean-atmosphere general circulation model (OAGCM) developed for studies of climate change and results from a hindcast experiment. The model includes various physical and technical improvements relative to an earlier version of the Hadley Centre OAGCM. A coupled spinup process is used to bring the model to equilibrium. Compared to uncoupled spinup methods this is computationally more expensive, but helps to counter climate drift arising from inadequate sampling of short time scale coupled variability when the components are equilibrated separately. Including sea ice advection and enhancing reference surface salinities in high southern latitudes in austral winter to promote bottom water formation during spinup appears to have stabilized the high-latitude drift exhibited in the earlier model’s control run. In the present study, the atmospheric control climate is stable on multi-century time scales with a drift in global average surface air temperature of only +0.016 K/century, despite a small residual drift in the deep ocean. The control climate is an improvement over the earlier model in several respects, notably in its variability on short time scales. Two anomaly runs are presented incorporating estimated forcing changes over the period 1860 to 1990 arising from greenhouse gases alone and from greenhouse gases plus the radiative scattering effect of sulphate aerosols. These allow validation of the model against the instrumental climate record. Inclusion of aerosol forcing gives a significantly better simulation of historical temperature patterns, although comparisons against recent sea ice trends are equivocal. These studies emphasize the potential importance of including additional forcing terms apart from greenhouse gases in climate simulations, and refining estimates of their spatial distribution and magnitude.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003820050155
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