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1.
The radiative impacts of the stratosphere in global warming simulations are investigated using abrupt CO2 quadrupling experiments of the Coupled Model Inter-comparison Project phase 5 (CMIP5), with a focus on stratospheric temperature and water vapor. It is found that the stratospheric temperature change has a robust bullhorn-like zonal-mean pattern due to a strengthening of the stratospheric overturning circulation. This temperature change modifies the zonal mean top-of-the-atmosphere energy balance, but the compensation of the regional effects leads to an insignificant global-mean radiative feedback (?0.02 ± 0.04 W m?2 K?1). The stratospheric water vapor concentration generally increases, which leads to a weak positive global-mean radiative feedback (0.02 ± 0.01 W m?2 K?1). The stratospheric moistening is related to mixing of elevated upper-tropospheric humidity, and, to a lesser extent, to change in tropical tropopause temperature. Our results indicate that the strength of the stratospheric water vapor feedback is noticeably larger in high-top models than in low-top ones. The results here indicate that although its radiative impact as a forcing adjustment is significant, the stratosphere makes a minor contribution to the overall climate feedback in CMIP5 models.  相似文献   

2.

Measurement of solar radiation was initiated in Girona, northeast of the Iberian Peninsula, in the late 1980s. Initially, two pyranometers were installed, one of them equipped with a shadowband for measuring the diffuse component. Two other pyranometers currently exist, both ventilated and one of them shadowed, with a sphere, and a pyrheliometer for measuring direct radiation. Additional instruments for other shortwave and longwave components, clouds, and atmospheric aerosols have been installed in recent years. The station is subject to daily inspection, data are saved at high temporal resolution, and instruments are periodically calibrated, all in accordance with the directions of the Baseline Surface Radiation Network. The present paper describes how the entire series of global solar radiation (1987–2014) and diffuse radiation (1994–2014) were built, including the quality control process. Appropriate corrections to the diffuse component were made when a shadowband was employed to make measurements. Analysis of the series reveals that annual mean global irradiance presents a statistically significant increase of 2.5 W m−2 (1.4 %) decade−1 (1988–2014 period), mainly due to what occurs in summer (5.6 W m−2 decade−1). These results constitute the first assessment of solar radiation trends for the northeastern region of the Iberian Peninsula and are consistent with trends observed in the regional surroundings and also by satellite platforms, in agreement with the global brightening phenomenon. Diffuse radiation has decreased at −1.3 W m−2 (−2 %) decade−1 (1994–2014 period), which is a further indication of the reduced cloudiness and/or aerosol load causing the changes.

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3.
The radiative forcings and feedbacks that determine Earth’s climate sensitivity are typically defined at the top-of-atmosphere (TOA) or tropopause, yet climate sensitivity itself refers to a change in temperature at the surface. In this paper, we describe how TOA radiative perturbations translate into surface temperature changes. It is shown using first principles that radiation changes at the TOA can be equated with the change in energy stored by the oceans and land surface. This ocean and land heat uptake in turn involves an adjustment of the surface radiative and non-radiative energy fluxes, with the latter being comprised of the turbulent exchange of latent and sensible heat between the surface and atmosphere. We employ the radiative kernel technique to decompose TOA radiative feedbacks in the IPCC Fourth Assessment Report climate models into components associated with changes in radiative heating of the atmosphere and of the surface. (We consider the equilibrium response of atmosphere-mixed layer ocean models subjected to an instantaneous doubling of atmospheric CO2). It is shown that most feedbacks, i.e., the temperature, water vapor and cloud feedbacks, (as well as CO2 forcing) affect primarily the turbulent energy exchange at the surface rather than the radiative energy exchange. Specifically, the temperature feedback increases the surface turbulent (radiative) energy loss by 2.87 W m?2 K?1 (0.60 W m?2 K?1) in the multimodel mean; the water vapor feedback decreases the surface turbulent energy loss by 1.07 W m?2 K?1 and increases the surface radiative heating by 0.89 W m?2 K?1; and the cloud feedback decreases both the turbulent energy loss and the radiative heating at the surface by 0.43 and 0.24 W m?2 K?1, respectively. Since changes to the surface turbulent energy exchange are dominated in the global mean sense by changes in surface evaporation, these results serve to highlight the fundamental importance of the global water cycle to Earth’s climate sensitivity.  相似文献   

4.
Severe air pollution with visibility deterioration has long been a focus in the North China Plain (NCP). In this study, concentration and light extinction analysis of PM2.5 chemical components were carried out from 2014 to 2017 to study the pollution characteristics in Baoding, a case city of the NCP. The annual average concentration of total PM2.5 components showed a declining trend, decreasing by 11 µg m−3 (water-soluble inorganic ions), 23 µg m−3 (carbonaceous aerosols), and 1796 ng m−3 (inorganic elements). Contributing 82.9% to the concentration of total ions, the dominant components, NH4+, NO3−, and SO42− became the main pollutants in PM2.5 pollution. Based on the IMPROVE algorithm, the average reconstructed PM2.5 mass concentration was 93 ± 69 µg m−3 during the observation period. Meanwhile, the light extinction coefficients were 373.8 ± 233.6 M m−1, 405.3 ± 300.1 M m−1, 554.3 ± 378.2 M m−1 and 1005.2 ± 750.3 M m−1, in spring, summer, autumn, and winter, respectively. Ammonium sulfate, ammonium nitrate, and organic matter were the largest contributors to light extinction, accounting for a total of 55%–77% in the four seasons. The bsca (light scattering by particles and gases) reconstructed from PM2.5 components (Rbsca) and the bsca converted from visibility (Vbsca) were compared to evaluate the performance of the IMPROVE algorithm, revealing a high correlation coefficient of 0.84. The high values of Vbsca were underestimated while the low values were overestimated, as determined through comparison with the one-to-ne line. Especially, when Rbsca > 1123 M m−1 (corresponding to < 2.0 km, approximately), Vbsca was underestimated by 17.6%. PM2.5 mass concentration and relative humidity also had an impact on the estimation.摘要华北平原大气污染与低能见度状况一直是人们关切的问题.本文通过分析2014 - 2017年PM2.5化学成分的浓度和消光效果, 研究了华北平原典型城市保定市的大气污染特征.结果表明, PM2.5组分的年均浓度显示下降趋势, 水溶性无机离子,碳质气溶胶和金属元素分别减少了11 µg m−3, 23 µg m−3和1796 ng m−3.NH4+,NO3−和SO42−是PM2.5污染的主要污染物, 三者之和占总离子浓度的82.9%.基于IMPROVE方程对细颗粒物进行重构, 在观测期间PM2.5质量浓度平均为93 ± 69 µg m−3, 春季,夏季,秋季和冬季的消光系数分别为373.8 ± 233.6 M m−1,405.3 ± 300.1 M m−1,554.3 ± 378.2 M m−1和1005.2 ± 750.3 M m−1.硫酸铵,硝酸铵和有机物对消光的贡献最大, 不同季节下占比达55% ~77%.通过PM2.5组分进行重构, 利用IMPROVE算法计算得到Rbsca, 用能见度测量值转换得到Vbsca, 二者具有较高的相关性 (r2=0.84) ;但存在Vbsca的高值被低估, Vbsca的低值被高估的现象;特别是当Rbsca > 1123 M m−1 (对应能见度约小于2.0 km) 时, Vbsca的值被低估了17.6%.高浓度PM2.5和高湿度对IMPROVE算法结果有显著的影响.  相似文献   

5.
程军  张瑾 《大气科学学报》2017,40(6):769-777
大西洋经向翻转环流(the Atlantic Meridional Overturning Circulation,AMOC)由低纬输送大量热量至高纬度北大西洋海区,并通过热通量由海洋输送给大气,主导了附近区域的气候形态,并对北半球尺度的气候变化产生显著影响。本文根据CMIP5多模式多增暖情景的预估模拟结果,通过与增暖前控制试验的对比发现,全球增暖可导致该海区湍流热通量的减小,且减小的幅度随增暖强度增大,模拟结果与观测一致。进一步研究发现,热通量的减小存在季节差异,冬季的减小幅度远大于夏季。结合淡水扰动试验的分析表明,全球增暖下AMOC强度的减弱导致大西洋经向热输送减少,进而导致高纬度北大西洋海洋向大气的热输送减小。  相似文献   

6.
Changes in land cover affect climate through the surface energy and moisture budgets, but these biogeophysical impacts of land use have not yet been included in General Circulation Model (GCM) simulations of 20th century climate change. Here, the importance of these effects was assessed by comparing climate simulations performed with current and potential natural vegetation. The northern mid-latitude agricultural regions were simulated to be approximately 1–2 K cooler in winter and spring in comparison with their previously forested state, due to deforestation increasing the surface albedo by approximately 0.1 during periods of snow cover. Some other regions such as the Sahel and India experienced a small warming due to land use. Although the annual mean global temperature is only 0.02 K lower in the simulation with present-day land use, the more local temperature changes in some regions are of a similar magnitude to those observed since 1860. The global mean radiative forcing by anthropogenic surface albedo change relative to the natural state is simulated to be −0.2 Wm2, which is comparable with the estimated forcings relative to pre-industrial times by changes in stratospheric and tropospheric ozone, N2O, halocarbons, and the direct effect of anthropogenic aerosols. Since over half of global deforestation has occurred since 1860, simulations of climate since that date should include the biogeophysical effects of land use.  相似文献   

7.
The finding that surface warming over the Arctic exceeds that over the rest of the world under global warming is a robust feature among general circulation models (GCMs). While various mechanisms have been proposed, quantifying their relative contributions is an important task in order to understand model behavior. Here we apply a recently proposed feedback analysis technique to an atmosphere–ocean GCM under two and four times CO2 concentrations which approximately lead to seasonally and annually sea ice-free climates. The contribution of feedbacks to Arctic temperature change is investigated. The surface warming in the Arctic is contributed by albedo, water vapour and large-scale condensation feedbacks and reduced by the evaporative cooling feedback. The surface warming contrast between the Arctic and the global averages (AA) is maintained by albedo and evaporative cooling feedbacks. The latter contributes to AA predominantly by cooling the low latitudes more than the Arctic. Latent heat transport into the Arctic increases and hence evaporative cooling plus large-scale condensation feedback contributes positively to AA. On the other hand, dry-static energy transport into the Arctic decreases and hence dynamical heating feedback contributes negatively to AA. An important contribution is thus made via changes in hydrological cycle and not via the ‘dry’ heat transport process. A larger response near the surface than aloft in the Arctic is maintained by the albedo, water vapour, and dynamical heating feedbacks, in which the albedo and water vapour feedbacks contribute through warming the surface more than aloft, and the dynamical heating feedback contributes by cooling aloft more than the surface. In our experiments, ocean and sea ice dynamics play a secondary role. It is shown that a different level of CO2 increase introduces a latitudinal and seasonal difference into the feedbacks.  相似文献   

8.
Lee  Wei-Liang  Liou  K. N.  He  Cenlin  Liang  Hsin-Chien  Wang  Tai-Chi  Li  Qinbin  Liu  Zhenxin  Yue  Qing 《Theoretical and Applied Climatology》2017,129(3-4):1373-1382

We investigate the snow albedo variation in spring over the southern Tibetan Plateau induced by the deposition of light-absorbing aerosols using remote sensing data from moderate resolution imaging spectroradiometer (MODIS) aboard Terra satellite during 2001–2012. We have selected pixels with 100 % snow cover for the entire period in March and April to avoid albedo contamination by other types of land surfaces. A model simulation using GEOS-Chem shows that aerosol optical depth (AOD) is a good indicator for black carbon and dust deposition on snow over the southern Tibetan Plateau. The monthly means of satellite-retrieved land surface temperature (LST) and AOD over 100 % snow-covered pixels during the 12 years are used in multiple linear regression analysis to derive the empirical relationship between snow albedo and these variables. Along with the LST effect, AOD is shown to be an important factor contributing to snow albedo reduction. We illustrate through statistical analysis that a 1-K increase in LST and a 0.1 increase in AOD indicate decreases in snow albedo by 0.75 and 2.1 % in the southern Tibetan Plateau, corresponding to local shortwave radiative forcing of 1.5 and 4.2 W m−2, respectively.

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9.

We study the spatio-temporal variability of Atmospheric Rivers (ARs) and associated integrated water vapor and atmospheric parameters over the Euro-Atlantic region using long-term reanalysis datasets. Winds, temperature, and specific humidity at different pressure levels during 1979–2018 are used to study the water vapor transport integrated between 1000 and 300 hPa (IVT300) in mapping ARs. The intensity of ARs in the North Atlantic has been increasing in recent times (2009–2018) with large decadal variability and poleward shift (~ 5° towards the North) in landfall during 1999–2018. Though different reanalysis datasets show similar spatial patterns of IVT300 in mapping ARs, bias in specific humidity and wind components led to IVT300 mean bias of 50 kg m−1 s−1 in different reanalysis products compared to ERA5. The magnitude of winds and specific humidity in the lower atmosphere (below 750 hPa) dominates the total column water vapor and intensity of ARs in the North Atlantic. Reanalysis datasets in the central North Atlantic show an IVT300 standard deviation of 200 kg m−1 s−1 which is around 33% of the ARs climatology (~ 600 kg m−1 s−1). Though ARs have a higher frequency of landfalling over Western Europe in winter half-year, the intensity of IVT300 in winter ARs is 3% lower than the annual mean. The lower frequency of ARs in the summer half-year shows 3% higher IVT300 than the annual mean. While ARs in the North Atlantic show a strong decadal change in frequency and path, the impact of the North Atlantic Oscillation (NAO) and Scandinavian blocking on the location of landfall of ARs are significant. Furthermore, there is a strong latitudinal dependence of the source of moisture flux in the open ocean, contributing to the formation and strengthening ARs.

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10.
 A coarse-grid global ocean general circulation model (OGCM) is used to determine the role of sub-grid scale eddy parametrization schemes in the response to idealized changes in the surface heat flux, of the same order as expected under increased atmospheric CO2 concentrations. Two schemes are employed. The first (H) incorporates standard horizontal mixing, whereas the second (G) combines both enhanced isopycnal mixing and eddy-induced transport. Uniform surface heating anomalies of +2 W m-2 and −2 W m-2 are applied for 50 years, and the results are compared with a control experiment in which no anomalous heating is imposed. A passive “heat” tracer is applied uniformly (at a rate of 2 W m-2 for 50 years) in a separate experiment. The sea-surface temperature response to global surface heating is generally larger in G, especially in the northern subtropical gyres, along the southern coast of Australia and off the Antarctic coast. A pronounced interhemispheric asymmetry (primarily arising from an anomalous response south of 35 °S) is evident in both H and G. The surface trapping of passive tracers in the Southern Hemisphere is generally greater in G than it is in H, and is particularly pronounced along the prime meridian (0 °E). Dynamical changes (i.e., changes in horizontal and vertical currents, convection, and preferred mixing and eddy transport pathways) enhance surface warming in the tropics and subtropics in both G and H. They are dominated by an anomalous meridional overturning centred on the equator, which may also operate in greenhouse warming experiments using coupled atmosphere-ocean GCMs. Over the Southern Ocean the passive tracer experiments and associated ventilation rates suggest that surface warming will be greater in G than in H. In fact, the contrast between the dynamical responses evident in G and H in the actual heating experiments leads to a situation in which the reverse is often true. Overall, dynamical changes enhance the interhemispheric assymetry, more so in G than in H. Received: August 1996/Accepted: 20 March 1997  相似文献   

11.
Results from large-eddy simulations and field measurements have previously shown that the velocity field is influenced by the boundary layer height, z i , during close to neutral, slightly unstable, atmospheric stratification. During such conditions the non-dimensional wind profile, φ m , has been found to be a function of both z/L and z i /L. At constant z/L, φ m decreases with decreasing boundary layer height. Since φ m is directly related to the parameterizations of the air–sea surface fluxes, these results will have an influence when calculating the surface fluxes in weather and climate models. The global impact of this was estimated using re-analysis data from 1979 to 2001 and bulk parameterizations. The results show that the sum of the global latent and sensible mean heat fluxes increase by 0.77 W m−2 or about 1% and the mean surface stress increase by 1.4 mN m−2 or 1.8% when including the effects of the boundary layer height in the parameterizations. However, some regions show a larger response. The greatest impact is found over the tropical oceans between 30°S and 30°N. In this region the boundary layer height influences the non-dimensional wind profile during extended periods of time. In the mid Indian Ocean this results in an increase of the mean annual heat fluxes by 2.0 W m−2 and an increase of the mean annual surface stress by 2.6 mN m−2.  相似文献   

12.
The sensitivity of the global climate is essentially determined by the radiative damping of the global mean surface temperature anomaly through the outgoing radiation from the top of the atmosphere (TOA). Using the TOA fluxes of terrestrial and reflected solar radiation obtained from the Earth radiation budget experiment (ERBE), this study estimates the magnitude of the overall feedback, which modifies the radiative damping of the annual variation of the global mean surface temperature, and compare it with model simulations. Although the pattern of the annually varying anomaly is quite different from that of the global warming, the analysis conducted here may be used for assessing the systematic bias of the feedback that operates on the CO2-induced warming of the surface temperature. In the absence of feedback effect, the outgoing terrestrial radiation at the TOA is approximately follows the Stefan-Boltzmann’s fourth power of the planetary emission temperature. However, it deviates significantly from the blackbody radiation due to various feedbacks involving water vapor and cloud cover. In addition, the reflected solar radiation is altered by the feedbacks involving sea ice, snow and cloud, thereby affecting the radiative damping of surface temperature. The analysis of ERBE reveals that the radiative damping is weakened by as much as 70% due to the overall effect of feedbacks, and is only 30% of what is expected for the blackbody with the planetary emission temperature. Similar feedback analysis is conducted for three general circulation models of the atmosphere, which was used for the study of cloud feedback in the preceding study. The sign and magnitude of the overall feedback in the three models are similar to those of the observed. However, when it is subdivided into solar and terrestrial components, they are quite different from the observation mainly due to the failure of the models to simulate individually the solar and terrestrial components of the cloud feedback. It is therefore desirable to make the similar comparison not only for the overall feedback but also for its individual components such as albedo- and cloud-feedbacks. Although the pattern of the annually-varying anomaly is quite different from that of global warming, the methodology of the comparative analysis presented here may be used for the identification of the systematic bias of the overall feedback in a model. A proposal is made for the estimation of the best guess value of climate sensitivity using the outputs from many climate models submitted to the Intergovernmental panel on Climate Change.  相似文献   

13.
A mooring equipped with 200 high-resolution temperature sensors between 6 and 404 m above the bottom was moored in 1890 m water depth above a steep, about 10° slope of Mount Josephine, NE-Atlantic. The sensors have a precision of less than 0.5 mK. They are synchronized via induction every 4 h so that the 400 m range is measured to within 0.02 s, every 1 s. Thin cables and elliptical buoyancy assured vertical mooring motions to be smaller than 0.1 m under maximum 0.2 m s−1 current speeds. The local bottom slope is supercritical for semidiurnal internal tides by a factor of two. Exploring a one-month record in detail, the observations show: 1/semidiurnal tidal dominance in variations of dissipation rate ε, eddy diffusivity Kz and temperature, but no significant correlation between the records of ε and total kinetic energy, 2/a variation with time over four orders of magnitude of 100-m vertically averaged ε, 3/a local minimum in density stratification between 50 and 100 m above the bottom, 4/a gradual decrease in daily or longer averaged ε and Kz by one order of magnitude over a vertical distance of 250 m, upwards from 150 m above the bottom, 5/monthly mean values of <[ε]> = 2 ± 0.5 × 10−7 m2 s−3, <[Kz]> = 8 ± 3 × 10−3 m2 s−1 averaged over the lower 150 m above the bottom.  相似文献   

14.
Xin Qu  Alex Hall 《Climate Dynamics》2014,42(1-2):69-81
Snow-albedo feedback (SAF) is examined in 25 climate change simulations participating in the Coupled Model Intercomparison Project version 5 (CMIP5). SAF behavior is compared to the feedback’s behavior in the previous (CMIP3) generation of global models. SAF strength exhibits a fivefold spread across CMIP5 models, ranging from 0.03 to 0.16 W m?2 K?1 (ensemble-mean = 0.08 W m?2 K?1). This accounts for much of the spread in 21st century warming of Northern Hemisphere land masses, and is very similar to the spread found in CMIP3 models. As with the CMIP3 models, there is a high degree of correspondence between the magnitudes of seasonal cycle and climate change versions of the feedback. Here we also show that their geographical footprint is similar. The ensemble-mean SAF strength is close to an observed estimate of the real climate’s seasonal cycle feedback strength. SAF strength is strongly correlated with the climatological surface albedo when the ground is covered by snow. The inter-model variation in this quantity is surprisingly large, ranging from 0.39 to 0.75. Models with large surface albedo when these regions are snow-covered will also have a large surface albedo contrast between snow-covered and snow-free regions, and therefore a correspondingly large SAF. Widely-varying treatments of vegetation masking of snow-covered surfaces are probably responsible for the spread in surface albedo where snow occurs, and the persistent spread in SAF in global climate models.  相似文献   

15.
Summary Vertical fluxes of momentum, sensible and latent heat have been estimated over the surface of the global oceans. A three-dimensional mesh grid 32 longitude points, 17 latitude points and 365 days from December 1, 1978 to November 30, 1979 is used to obtain seasonal and annual mean values of the surface fluxes. The global climatology shows the seasonal variation, the continental influence, the principal ocean currents and the typical middle latitude (30°–50°) and tropical effects (30°S–30°N). The annual mean of latent heat shows greater flux over the subtropical regions (~ 280 W/m2) than in the polar regions (~ 80 W/m2). On the other hand, the annual mean of sensible heat shows greater flux over the polar regions (~ 100 W/m2) than in the tropics (~ 40 W/m2). Time series analyses of the daily estimates of the surface fluxes show greater energy at high frequencies due to the surface effect; however, the low-frequency spectra show relatively high energy at the 30- to 50-day mode, especially for the middle latitude regions. The 30–50 day filtered data for the surface fluxes, presented in time/latitude cross-sections for the middle latitude regions show a westerly wave propagation with wave numberK = 2 and phase speed of the order of 12 degrees/day from June to August over the southern hemisphere at 55°S.
Zusammenfassung Die vorliegende Studie beschäftigt sich mit der Einschätzung der vertikalen Impuls-Flüsse und der Flüsse von sensibler und latenter Wärme über der gesamten Meeresoberfläche. Ein dreidimensionales Gitter mit 32 × 17 Punkten und Daten von 365 Tagen (von 1. 12. 1978 bis 30. 11. 1979) wird benutzt, um sowohl Jahreszeiten als auch Jahresmittelwerte der Oberflächenflüsse zu erhalten. Die globale Klimatologie zeigt die jahreszeitlichen Schwankungen, den kontinentalen Einfluß, die wichtigsten Meeresströmungen und die typischen Effekte der mittleren Breiten (30°–50°) und der Tropen (30°S–30°N). Das Jahresmittel latenter Wärme weist größere Flüsse über subtropischen Regionen (ca. 280 W/m2) als über polaren Regionen (ca. 80 W/m2) auf, während andererseits das Jahresmittel sensibler Wärme über Polarregionen (ca. 100 W/m2) größere Flüsse als über den Tropen (ca. 40 W/m2) aufweist. Zeitreihen-Analysen der täglichen Schätzwerte von Oberflächenflüssen deuten auf mehr Energie bei hohen Frequenzen aufgrund des Oberflächeneffekts hin; in jedem Fall zeigen die Niederfrequenz-Spektren relativ hohe Energie in den 30 – 50-Tage-Perioden, besonders für mittlere Breiten. Die über einen Zeitraum von 30 – 50 Tagen gesammelten Daten der Oberflächenflüsse dargestellt in Zeit-Breiten-Querschnitten für mittlere Breiten zeigen von Juni bis August über der südlichen Hemisphäre bei 55°S eine Ausbreitung der westlichen Wellen mit der WellenzahlK = 2 und einer Phasengeschwindigkeit im Ausmaß von 12° pro Tag.

With 7 Figures  相似文献   

16.
This study examines in detail the ‘atmospheric’ radiative feedbacks operating in a coupled General Circulation Model (GCM). These feedbacks (defined as the change in top of atmosphere radiation per degree of global surface temperature change) are due to responses in water vapour, lapse rate, clouds and surface albedo. Two types of radiative feedback in particular are considered: those arising from century scale ‘transient’ warming (from a 1% per annum compounded CO2 increase), and those operating under the model’s own unforced ‘natural’ variability. The time evolution of the transient (or ‘secular’) feedbacks is first examined. It is found that both the global strength and the latitudinal distributions of these feedbacks are established within the first two or three decades of warming, and thereafter change relatively little out to 100 years. They also closely approximate those found under equilibrium warming from a ‘mixed layer’ ocean version of the same model forced by a doubling of CO2. These secular feedbacks are then compared with those operating under unforced (interannual) variability. For water vapour, the interannual feedback is only around two-thirds the strength of the secular feedback. The pattern reveals widespread regions of negative feedback in the interannual case, in turn resulting from patterns of circulation change and regions of decreasing as well as increasing surface temperature. Considering the vertical structure of the two, it is found that although positive net mid to upper tropospheric contributions dominate both, they are weaker (and occur lower) under interannual variability than under secular change and are more narrowly confined to the tropics. Lapse rate feedback from variability shows weak negative feedback over low latitudes combined with strong positive feedback in mid-to-high latitudes resulting in no net global feedback—in contrast to the dominant negative low to mid-latitude response seen under secular climate change. Surface albedo feedback is, however, slightly stronger under interannual variability—partly due to regions of extremely weak, or even negative, feedback over Antarctic sea ice in the transient experiment. Both long and shortwave global cloud feedbacks are essentially zero on interannual timescales, with the shortwave term also being very weak under climate change, although cloud fraction and optical property components show correlation with global temperature both under interannual variability and transient climate change. The results of this modelling study, although for a single model only, suggest that the analogues provided by interannual variability may provide some useful pointers to some aspects of climate change feedback strength, particularly for water vapour and surface albedo, but that structural differences will need to be heeded in such an analysis.  相似文献   

17.
Abstract

Ground‐based measurements of stratospheric NO2, using absorption spectroscopy of twilight sky in the spectral region 437–451 nm, have been made at Calgary (51.08°N, 114.13°W), Alberta, Canada, during the period December 1978‐March 10, 1979. The NO2 showed a rather steady behaviour in the month of December when there was no stratospheric warming in progress; the monthly average of the afternoon vertical column abundance for December was 1.7 × 1015 cm2. In the rest of the observation period the NO2 showed a complex behaviour, but this behaviour appears to be explicable in terms of the stratospheric circulation changes taking place in that period due to the occurrence of a stratospheric warming event.  相似文献   

18.
A time series of microwave radiometric profiles over Arctic Canada’s Cape Bathurst (70°N, 124.5°W) flaw lead polynya region from 1 January to 30 June, 2008 was examined to determine the general characteristics of the atmospheric boundary layer in winter and spring. A surface based or elevated inversion was present on 97% of winter (January–March) days, and on 77% of spring (April–June) days. The inversion was the deepest in the first week of March (≈1100 m), and the shallowest in June (≈250 m). The mean temperature and absolute humidity from the surface to the top of the inversion averaged 250.1 K (−23.1°C), and 0.56 × 10−3 kg m−3 in winter, and in spring averaged 267.5 K (−5.6°C), and 2.77 × 10−3 kg m−3. The median winter atmospheric boundary-layer (ABL) potential temperature profile provided evidence of a shallow, weakly stable internal boundary layer (surface to 350 m) topped by an inversion (350–1,000 m). The median spring profile showed a shallow, near-neutral internal boundary layer (surface to 350 m) under an elevated inversion (600–800 m). The median ABL absolute humidity profiles were weakly positive in winter and negative in spring. Estimates of the convergence of sensible heat and water vapour from the surface that could have produced the turbulent internal boundary layers of the median profiles were 0.67 MJ m−2 and 13.1 × 10−3 kg m−2 for the winter season, and 0.66 MJ m−2 and 33.4 × 10−3 kg m−2 for the spring season. With fetches of 10–100 km, these accumulations may have resulted from a surface sensible heat flux of 15–185 W m−2, plus a surface moisture flux of 0.001–0.013 mm h−1 (or a latent heat flux of 0.7–8.8 W m−2) in winter, and 0.003–0.033 mm h−1 (or a latent heat flux of 2–22 W m−2) in spring.  相似文献   

19.
Summary A suite of simulations with the HadCM3LC coupled climate-carbon cycle model is used to examine the various forcings and feedbacks involved in the simulated precipitation decrease and forest dieback. Rising atmospheric CO2 is found to contribute 20% to the precipitation reduction through the physiological forcing of stomatal closure, with 80% of the reduction being seen when stomatal closure was excluded and only radiative forcing by CO2 was included. The forest dieback exerts two positive feedbacks on the precipitation reduction; a biogeophysical feedback through reduced forest cover suppressing local evaporative water recycling, and a biogeochemical feedback through the release of CO2 contributing to an accelerated global warming. The precipitation reduction is enhanced by 20% by the biogeophysical feedback, and 5% by the carbon cycle feedback from the forest dieback. This analysis helps to explain why the Amazonian precipitation reduction simulated by HadCM3LC is more extreme than that simulated in other GCMs; in the fully-coupled, climate-carbon cycle simulation, approximately half of the precipitation reduction in Amazonia is attributable to a combination of physiological forcing and biogeophysical and global carbon cycle feedbacks, which are generally not included in other GCM simulations of future climate change. The analysis also demonstrates the potential contribution of regional-scale climate and ecosystem change to uncertainties in global CO2 and climate change projections. Moreover, the importance of feedbacks suggests that a human-induced increase in forest vulnerability to climate change may have implications for regional and global scale climate sensitivity.  相似文献   

20.
The link between the sea-ice cover of the Amundsen Gulf and the overlying atmospheric boundary layer was explored on a weekly timestep from winter to summer 2008. The total sea-ice cover was around 97% (3% leads) from 7 January to 21 April. From 28 April to 12 May, the total sea-ice cover approached 100%. From May 19, the total sea-ice declined rapidly to its July minimum of 3%. During the winter, a turbulent internal boundary layer (IBL), attributed to the upward flux of sensible heat (mean = 46 W m−2), was present in most of the mean daily potential temperature profiles. The mean latent heat flux was 1.7 Wm−2. A turbulent IBL was also present in most of the mean daily profiles for early spring. Surface fluxes were not estimated. During late spring and early summer, a stable IBL, attributed to the downward flux of sensible heat (mean = −19 W m−2), was present in most of the potential temperature profiles. Both downward and upward fluxes of latent heat occurred in this period (means = −3.3 and 1.1 W m−2). The sensible heat flux estimates are consistent with the results of others; however, the latent heat flux estimates may be too small due to condensation/deposition within the IBL. The unconsolidated nature of the pack ice in the Amundsen Gulf, and the low sea-surface temperatures following break-up, were critical factors controlling the presence and type of IBL.  相似文献   

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