Past,present and future vegetation-cloud feedbacks in the Amazon Basin     

E. Pinto  Y. Shin  S. A. Cowling  C. D. Jones 《Climate Dynamics》2009,32(6):741-751

To begin exploring the underlying mechanisms that couple vegetation to cloud formation processes, we derive the lifting condensation level (LCL) to estimate cumulus cloud base height. Using a fully coupled land–ocean–atmosphere general circulation model (HadCM3LC), we investigate Amazonian forest feedbacks on cloud formation over three geological periods; modern-day (a.d. 1970–1990), the last glacial maximum (LGM; 21 kya), and under a future climate scenario (IS92a; a.d. 2070–2090). Results indicate that for both past and future climate scenarios, LCL is higher relative to modern-day. Statistical analyses indicate that the 800 m increase in LCL during the LGM is related primarily to the drier atmosphere promoted by lower tropical sea surface temperatures. In contrast, the predicted 1,000 m increase in LCL in the future scenario is the result of a large increase in surface temperature and reduced vegetation cover.  相似文献   

Arctic climate change: observed and modelled temperature and sea-ice variability   总被引：6，自引：0，他引：6  

OLA M. JOHANNESSEN  LENNART BENGTSSON  MARTIN W. MILES  SVETLANA I. KUZMINA  VLADIMIR A. SEMENOV  GENRIKH V. ALEKSEEV  REI P. NAGURNYI  VICTOR F. ZAKHAROV  LEONID P. BOBYLEV  LASSE H. PETTERSSON  KLAUS HASSELMANN  HOWARD P. CATTLE 《地球，A辑:动力气象学与海洋学》2004,56(4):328-341

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Downward atmospheric longwave irradiance under clear and cloudy skies: Measurement and parameterization     

《Journal of Atmospheric and Solar》2003,65(10):1107-1116

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Density currents in the two-layer flow: an example of Dardanelles outflow     

《Oceanologica Acta》2003,26(3):243-253

Observations from hydrographic surveys are used to describe the density current flowing through the Dardanelles strait into the Marmara Sea. Aegean water plunges below the surface and flows into the Marmara Sea. This flow joins into the Marmara Sea as a negatively buoyant plume and sinks through the deeper parts. Seasonal variation in the incoming water density results in the observing mainly two different forms of the density current in this area. These two forms are boundary currents and intrusion. Boundary currents were observed as a dense bottom current during the winter when the inflowing water density attains to annual maxima and as an overflow during the autumn when the inflowing water density drops to annual minimum. Intrusion form of the density current was observed during the summer.  相似文献   

A geographical analysis of warm season lightning/landscape interactions across Colorado,USA     

《Applied geography (Sevenoaks, England)》2016

This article analyzes lightning/landscape interactions across the State of Colorado. Ten years (2003–2012) of warm season cloud-to-ground (CG) lightning activity are mapped at 500 × 500 m² to characterize the distribution of thunderstorm activity. Geospatial analyses quantify lightning activity by elevation, physiographic region, and mountain range, and time-series animations outline the general movement of thunderstorms. From these spatio-temporal perspectives, our objective is to elucidate lightning/landscape interactions as they occur over a topographically and climatologically diverse landscape. The information aids meteorologists by exposing orographic and rainshadow effects, mesoscale meteorological effects, fluxes of moisture sources, thunderstorm initiation zones, and thunderstorm movements. Other benefits extend to wildland fire managers, those who maintain lightning-vulnerable infrastructures, and, from a human risk perspective, an overall awareness to those who work and play outdoors. Major findings include (1) elevation alone does not determine the degree of lightning activity, (2) across the state's mountain ranges, lightning density varies considerably, but the number of lightning days does not, and (3) the time of lightning initiation and maxima varies by elevation, with higher mountain elevations experiencing most activity 1 h before lower mountain elevations, and 3 h before lower Great Plains locations.  相似文献   

Towards the Construction of Climate Change Scenarios   总被引：3，自引：2，他引：1  

John F. B. Mitchell  T. C. Johns  M. Eagles  W. J. Ingram  R. A. Davis 《Climatic change》1999,41(3-4):547-581

Climate impacts assessments need regional scenarios of climate change for a wide range of projected emissions. General circulation models (GCMs) are the most promising approach to providing such information, but as yet there is considerable uncertainty in their regional projections and they are still too costly to run for a large number of emission scenarios. Simpler models have been used to estimate global-mean temperature changes under a range of scenarios. In this paper we investigate whether a fixed pattern from a GCM experiment scaled by global-mean temperature changes from a simple model provides an acceptable estimate of the regional climate change over a range of scenarios. Changes estimated using this approximate approach are evaluated by comparing them with results from ensembles of a coupled ocean-atmosphere model. Five specific emissions scenarios are considered. For increases in greenhouse gases only, the 'error' in annual mean temperature for the cases considered is smaller than the sampling error due to the model's internal variability. The method may break down for scenarios of stabilisation of concentrations, because the patterns change as the model approaches equilibrium. The inclusion of large local perturbations due to sulphate aerosols can lead to significant deviations of the temperature pattern from that obtained using greenhouse gases alone. Combining separate patterns for the responses to greenhouse gases and aerosols may improve the accuracy of approximation. Finally, the accuracy of the scaling approach is more difficult to assess for deriving changes in regional precipitation because many of the regional changes are not statistically significant in the climate change projections considered here. If precipitation changes are only marginally significant in other models, the apparent disagreement between different models may be as much due to sampling error as to genuine differences in model response.  相似文献   

A high resolution AMIP integration using the Hadley Centre model HadAM2b     

R. A. Stratton 《Climate Dynamics》1999,15(1):9-28

 A high resolution (0.833° latitude by 1.25° longitude) AMIP (Atmospheric Model Intercomparison Project) integration is compared with a control integration at standard resolution (2.5° by 3.75°). Both integrations use HadAM2b, a recent version of the Hadley Centre atmospheric general circulation model. ECMWF reanalysis data for the AMIP period (1979–1988), together with other climatologies, are used to evaluate the results. An additional integration at standard resolution using the high resolution shorter time step is used to help distinguish between changes due to model resolution and those which are due to time step dependencies in the physical parametrizations. Enhanced resolution increases the vertical motion, intensifies the hydrological cycle, reduces slightly the model’s cold bias in the troposphere, shifts the westerly jets poleward and tends to increase the eddy kinetic energy and variability of the model. The high resolution simulation has less mid-latitude cloud, so altering the radiation balance. There is no evidence to suggest that increasing resolution has an impact on the model’s response to SST forcing. Received: 7 October 1997 / Accepted: 16 June 1998  相似文献   

Checking for model consistency in optimal fingerprinting   总被引：3，自引：2，他引：1  

M. R. Allen  S. F. B. Tett 《Climate Dynamics》1999,15(6):419-434

 Current approaches to the detection and attribution of an anthropogenic influence on climate involve quantifying the level of agreement between model-predicted patterns of externally forced change and observed changes in the recent climate record. Analyses of uncertainty rely on simulated variability from a climate model. Any numerical representation of the climate is likely to display too little variance on small spatial scales, leading to a risk of spurious detection results. The risk is particularly severe if the detection strategy involves optimisation of signal-to-noise because unrealistic aspects of model variability may automatically be given high weight through the optimisation. The solution is to confine attention to aspects of the model and of the real climate system in which the model simulation of internal climate variability is adequate, or, more accurately, cannot be shown to be deficient. We propose a simple consistency check based on standard linear regression which can be applied to both the space-time and frequency domain approaches to optimal detection and demonstrate the application of this check to the problem of detection and attribution of anthropogenic signals in the radiosonde-based record of recent trends in atmospheric vertical temperature structure. The influence of anthropogenic greenhouse gases can be detected at a high confidence level in this diagnostic, while the combined influence of anthropogenic sulphates and stratospheric ozone depletion is less clearly evident. Assuming the time-scales of the model response are correct, and neglecting the possibility of non-linear feedbacks, the amplitude of the observed signal suggests a climate sensitivity range of 1.2–3.4 K, although the upper end of this range may be underestimated by up to 25% due to uncertainty in model-predicted response patterns. Received: 9 December 1997 / Accepted: 24 December 1998  相似文献   

Evaluation of the North Atlantic Oscillation as simulated by a coupled climate model   总被引：12，自引：1，他引：11  

T. J. Osborn  K. R. Briffa  S. F. B. Tett  P. D. Jones  R. M. Trigo 《Climate Dynamics》1999,15(9):685-702

 The realism of the Hadley Centre’s coupled climate model (HadCM2) is evaluated in terms of its simulation of the winter North Atlantic Oscillation (NAO), a major natural mode of the Northern Hemisphere atmosphere that is currently the subject of considerable scientific interest. During 1400 y of a control integration with present-day radiative forcing levels, HadCM2 exhibits a realistic NAO associated with spatial patterns of sea level pressure, synoptic activity, temperature and precipitation anomalies that are very similar to those observed. Spatially, the main model deficiency is that the simulated NAO has a teleconnection with the North Pacific that is stronger than observed. In a temporal sense the simulation is compatible with the observations if the recent observed trend (from low values in the 1960s to high values in the early 1990s) in the winter NAO index (the pressure difference between Gibraltar and Iceland) is ignored. This recent trend is, however, outside the range of variability simulated by the control integration of HadCM2, implying that either the model is deficient or that external forcing is responsible for the variation. It is shown, by analysing two ensembles, each of four HadCM2 integrations that were forced with historic and possible future changes in greenhouse gas and sulphate aerosol concentrations, that a small part of the recent observed variation may be a result of anthropogenic forcing. If so, then the HadCM2 experiments indicate that the anthropogenic effect should reverse early next century, weakening the winter pressure gradient between Gibraltar and Iceland. Even combining this anthropogenic forcing and internal variability cannot explain all of the recent observed variations, indicating either some model deficiency or that some other external forcing is partly responsible. Received: 20 August 1998 / Accepted: 12 May 1999  相似文献   

Inter-decadal modulation of the impact of ENSO on Australia   总被引：23，自引：2，他引：21  

S. Power  T. Casey  C. Folland  A. Colman  V. Mehta 《Climate Dynamics》1999,15(5):319-324

 The success of an ENSO-based statistical rainfall prediction scheme and the influence of ENSO on Australia are shown to vary in association with a coherent, inter-decadal oscillation in surface temperature over the Pacific Ocean. When this Inter-decadal Pacific Oscillation (IPO) raises temperatures in the tropical Pacific Ocean, there is no robust relationship between year-to-year Australian climate variations and ENSO. When the IPO lowers temperature in the same region, on the other hand, year-to-year ENSO variability is closely associated with year-to-year variability in rainfall, surface temperature, river flow and the domestic wheat crop yield. The contrast in ENSO’s influence between the two phases of the IPO is quite remarkable. This highlights exciting new avenues for obtaining improved climate predictions. Received: 21 October 1998 / Accepted: 27 November 1998  相似文献