Decadal and centennial variability of the southern semiannual oscillation simulated in the GFDL coupled GCM   总被引：1，自引：0，他引：1  

I. Simmonds  D. J. Walland 《Climate Dynamics》1997,14(1):45-53

 We investigate the behavior of the semiannual oscillation (SAO) in surface pressure and 500 hPa baroclinicity at high southern latitudes in a 1000-year GFDL coupled ocean-atmosphere GCM run. The model represents this feature but is shown to underestimate its amplitude and percentage of variance explained in the midlatitudes. South of 60 °S the simulation of the pressure oscillation, although somewhat too weak, is considerably better. Our analysis reveals significant interannual, decadal and centennial variability in the modeled SAO. While there is only a short historical record of observational data in the middle and high southern latitudes, existing studies suggest that the strength of the SAO does show significant variability on at least the first two of these time scales. Strong relationships between the semiannual cycles of surface pressure and baroclinicity are apparent in the model output, reinforcing the findings in earlier studies that the differing annual march of temperature between the midlatitudes and the Antarctic coast leads to a semiannual component in the baroclinicity and thence the surface pressure. We draw attention to extended periods when the model SAO is weak and strong, and have investigated the nature of the circulation during each period. The GFDL model results suggest that a significant proportion of the SAO variation was associated more with variations in the strength of the winter pressure maximum rather than the springtime minimum. The extent to which this and other aspects of the modeled longterm variability are related to actual atmospheric structure must await the availability of longer data records. Received: 11 November 1996 / Accepted: 28 July 1997  相似文献   

Large scale and sub-regional connections in the lead up to summer heat wave and extreme rainfall events in eastern Australia   总被引：1，自引：1，他引：0  

Ghyslaine Boschat  Alexandre Pezza  Ian Simmonds  Sarah Perkins  Tim Cowan  Ariaan Purich 《Climate Dynamics》2015,44(7-8):1823-1840

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Comparison of two periods of North Sea herring stock management: success, failure, and monetary value     

Simmonds  E. John 《ICES Journal of Marine Science》2007,64(4):686-692

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Hydroxyl Radical Concentrations Estimated from Measurements of Trichloroethylene during the EASE/ACSOE Campaign at Mace Head, Ireland during July 1996     

R. G. Derwent  N. Carslaw  P. G. Simmonds  M. Bassford  S. O'Doherty  D. B. Ryall  M. J. Pilling  A. C. Lewis  J. B. McQuaid 《Journal of Atmospheric Chemistry》1999,34(2):185-205

During the EASE/OXICOA campaign of the NERC ACSOE programme, trichloroethylene and a wide range of man-made halocarbons and radiatively-active trace gases were monitored with high precision and high frequency throughout July 1996 at Mace Head on the Atlantic Ocean coast of Ireland. Trichloroethylene concentrations in concert with many other trace gases became elevated as regionally-polluted and photochemically-aged air masses reached Mace Head. However, as the anticyclonic air masses retreated during 19 and 20 July, trace gas concentrations remained elevated for a significant period. During this 2–4 day period, trichloroethylene concentrations decayed significantly, though the concentrations of the other more chemically-inert trace gases did not. A detailed interpretation of this behaviour using a Lagrangian dispersion model has allowed the estimation of average and peak OH radical concentrations of 3 and 9×10⁶ molecule cm^-3, respectively, during the travel from the source areas in the U.K. and the low countries out to Mace Head. Using a simple box model, the available Mace Head measurements, when combined into a detailed chemical mechanism, generated OH radical concentrations which peaked at 7×10⁶ molecule cm^-3, in close agreement with the estimates based on trichloroethylene decay.  相似文献   

Vertical characteristics of cyclonic tracks over the eastern Mediterranean during the cold period of the year     

H. A. Flocas  P. Kountouris  J. Kouroutzoglou  M. Hatzaki  K. Keay  I. Simmonds 《Theoretical and Applied Climatology》2013,112(3-4):375-388

The vertical structure of surface cyclonic tracks affecting the eastern Mediterranean region is studied on a climatological basis for the cold period of the year. The dataset used is the 1°?×?1° ERA-40 Reanalysis for a 40-year period (1962–2001). The vertical tracking of surface cyclonic tracks was performed with the aid of the Melbourne University Vertical Tracking Algorithm. It was found that about 83 % of the cyclones were extended up to the 500-hPa level and almost 65 % up to 200-hPa level, implying that the cyclones are in general well organized. The surface tracks that originate within the examined area exhibit the smallest vertical extension, intensity, radius, and depth compared to the cyclones originating in the other sectors. Moreover, the 500-hPa counterparts for the said cyclones are mainly located to the north-west or south-west of the surface cyclone position, consistent with the baroclinic character of the Mediterranean cyclones. The zonal (eastward) component of motion predominates both at the surface and at 500 hPa.  相似文献   

Sensitivity of the distribution of thunderstorms to sea surface temperatures in four Australian east coast lows     

Christopher R. S. Chambers  Gary B. Brassington  Kevin Walsh  Ian Simmonds 《Meteorology and Atmospheric Physics》2015,127(5):499-517

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Declining summer snowfall in the Arctic: causes, impacts and feedbacks   总被引：1，自引：0，他引：1  

James A. Screen  Ian Simmonds 《Climate Dynamics》2012,38(11-12):2243-2256

Recent changes in the Arctic hydrological cycle are explored using in situ observations and an improved atmospheric reanalysis data set, ERA-Interim. We document a pronounced decline in summer snowfall over the Arctic Ocean and Canadian Archipelago. The snowfall decline is diagnosed as being almost entirely caused by changes in precipitation form (snow turning to rain) with very little influence of decreases in total precipitation. The proportion of precipitation falling as snow has decreased as a result of lower-atmospheric warming. Statistically, over 99% of the summer snowfall decline is linked to Arctic warming over the past two decades. Based on the reanalysis snowfall data over the ice-covered Arctic Ocean, we derive an estimate for the amount of snow-covered ice. It is estimated that the area of snow-covered ice, and the proportion of sea ice covered by snow, have decreased significantly. We perform a series of sensitivity experiments in which inter-annual changes in snow-covered ice are either unaccounted for, or are parameterized. In the parameterized case, the loss of snow-on-ice results in a substantial decrease in the surface albedo over the Arctic Ocean, that is of comparable magnitude to the decrease in albedo due to the decline in sea ice cover. Accordingly, the solar input to the Arctic Ocean is increased, causing additional surface ice melt. We conclude that the decline in summer snowfall has likely contributed to the thinning of sea ice over recent decades. The results presented provide support for the existence of a positive feedback in association with warming-induced reductions in summer snowfall.  相似文献   

Carbon tetrachloride lifetimes and emissions determined from daily global measurements during 1978–1985     

P. G. Simmonds  D. M. Cunnold  F. N. Alyea  C. A. Cardelino  A. J. Crawford  R. G. Prinn  P. J. Fraser  R. A. Rasmussen  R. D. Rosen 《Journal of Atmospheric Chemistry》1988,7(1):35-58

Seven years of daily gas chromatographic measurements of CCl₄ at the five globally distributed ALE/GAGE surface sites are reported. It is determined that CCl₄ has been accumulating in the atmosphere at a rate of 1.3±0.1%/yr over the period 1978–1985 and that the releases of CCl₄ into the atmosphere have remained fairly constant, with the smallest releases in 1981–1982. Using an inversion scheme based on a nine box model of the atmosphere, we infer a CCl₄ lifetime of approximately 40 yr, an inventory on 1 July 1978 of (2.08±0.07)×10⁹ kg and an average rate of release over the period 1978–1985 of (0.9±0.9)×10⁷ kg/yr. These results produce excellent agreement with a release scenario derived from global production estimates for CCl₄ and the major CCl₄ byproduct, the chlorofluorocarbons. However, to obtain this consistency, it is necessary that our current ALE/GAGE absolute calibration standard be reduced approximately 25% thus bringing it into agreement with measurements by Yokohata et al. (1985) and Hanst et al. (1975).  相似文献   

Which are better, random or systematic acoustic surveys? A simulation using North Sea herring as an example   总被引：7，自引：1，他引：7  

Simmonds  E. J.; Fryer  R. J. 《ICES Journal of Marine Science》1996,53(1):39-50

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Segregation and Interpretation of Ozone and Carbon Monoxide Measurements by Air Mass Origin at the TOR Station Mace Head, Ireland from 1987 to 1995     

P. G. Simmonds  S. Seuring  G. Nickless  R. G. Derwent 《Journal of Atmospheric Chemistry》1997,28(1-3):45-59

Three independent methods have been used to sort the ozone, carbonmonoxide, and other radiatively important trace gases measured at Mace Head,Ireland, and thereby distinguish clean air masses transported over the NorthAtlantic from the more polluted air masses which have recently travelledfrom the European continent. Over the period April 1987–June 1995 theNorthern Hemisphere surface ozone baseline concentrations exhibited a meanconcentration of 34.8 ppb, with a small positive trend (+0.19 ppbyr^-1), while the corresponding trend in air originating fromthe polluted European areas was negative (–0.39 ppbyr^-1). Carbon monoxide measurements from March 1990 toDecember 1994 showed negative trends for both the unpolluted (–0.17ppb yr^-1) and polluted data (–13.6 ppbyr^-1). Overall the continent of Europe was shown to be a smallnet sink of 2.6 ppb for all occasions when European air was transported tothe North Atlantic.  相似文献