Influence of water vapor and aerosol on the integral transparency of the atmosphere

The temporal variability of the total atmospheric water content W and the connection of the coefficient of integral transparency P ₂, reduced to the air mass m = 2, with W and aerosol optical depth τ _a ,λ₀ at a wavelength of 550 nm were analyzed and studied from the observational data of the Meteorological Observatory of Moscow State University for 50 years (1955–2004). The regression equations between mean daily and monthly τ _a ,λ₀ and τ₂ = ?ln P ₂ were derived in different months and seasons and can be used for retrieving τ _a ,λ₀ from the coefficient of the integral transparency for the temperate latitudes. The P ₂ intervals are given for which these equations can be used.     

On the role of cloud adjustment time scale in simulating precipitation with Relaxed Arakawa–Schubert convection scheme

The precipitation by Relaxed Arakawa–Schubert cumulus parameterization in a General Circulation Model (GCM) is sensitive to the choice of relaxation parameter or specified cloud adjustment time scale. In the present study, we examine sensitivity of simulated precipitation to the choice of cloud adjustment time scale (τ_adj) over different parts of the tropics using National Center for Environmental Prediction (NCEP) Seasonal Forecast Model (SFM) during June–September. The results show that a single specified value of τ_adj performs best only over a particular region and different values are preferred over different parts of the world. To find a relation between τ_adj and cloud depth (convective activity) we choose six regions over the tropics. Based on the observed relation between outgoing long-wave radiation and τ_adj,?we propose a linear cloud-type dependent relaxation parameter to be used in the model. The simulations over most parts of the tropics show improved results due to this newly formulated cloud-type dependent relaxation parameter.     

Estimates of effective aerosol optical depths from spectral solar radiation measurements

Summary This study reports a 37-year long record of direct beam spectral irradiance measurements made in Athens, Greece. An analysis of aerosol effects on the spectral distribution of solar radiation through effective optical depths, are presented. Thus, spectrally resolved aerosol optical depths were calculated and analyzed for the period 1954–1990. Summertime aerosol optical depths were found to be larger than winter values, while their seasonal variations were related to varying weather conditions throughout the year. The interrelationships between effective optical depths were found to be linear and were related strongly to microphysics of aerosol loading in the atmosphere. For the period 1962–1983 as wavelength exponent ₀ values ranged between 0.76–1.14 the spectrally resolved optical depths were found to increase markedly with respect to remaining periods 1954–1961 and 1984–1990 in which ₀ values ranged between 1.16–1.39. A minimum in aerosol optical depths, believed to be near background levels, was reached during period 1954–1957, while there was some indication that both optical depths continued to decrease reaching background levels at the end of the study period. From the long-term variation of aerosol effective optical depths some interesting information on the time evolution of air quality in Athens was gained. In addition, their frequency distribution, temporal daily variations and some remarks on photosynthetically active radiation for plant development, are presented and discussed.With 7 Figures     

El Chichón – influence on aerosol optical depth and direct,diffuse and total solar irradiances at Vancouver,B.C.

Abstract

Solar radiation data for Vancouver, B.C. were used to determine the increase in aerosol optical depth and the changes in the total, direct, diffuse and net short‐wave radiation fluxes associated with the presence of aerosol that originated from the eruption of El Chichón (Mexico) in April 1982. The aerosol optical depth increased by 400% resulting in reductions of 33% in the direct and increases of 80% in the diffuse short‐wave radiation. These maximum changes were experienced some 9 months following the eruption. The relative insensitivity of the total short‐wave radiation (maximum reduction was 6%) suggests that the volcanic cloud was a strong forward scatterer rather than an absorber or back scatterer. Moreover, interannual variability in the surface albedo and a negative feedback associated with the dependence of the surface albedo on the directionality of the incident radiation resulted in no consistent change in the amount of short‐wave radiation absorbed by the Earth's surface.     

大气中臭氧9.6μ带辐射收支的计算

计算大气中的长波辐射时,吸收气体的光学厚度要作气压订正,一般取气压订正后的光学厚度u′=(p/p_0)~K,对于O_3的9.6μ带,理论分析和实验都表明K是u和p的函数,气压订正可取 u′=(p/p_0)~(K(u,p))=uf(u,p). 我们以Walshaw的实验为基础,求出f(u,p)的囹形,并求出辐射通量及辐射通量散度的计算表。 当u很小时,弱线近似成立。漫射辐射的吸收率A_f=1-exp(-2su/d),K→0。在u→0时,dA_f/du=s2/d为一常量。     

MANTRA ‐ A Balloon Mission to Study the Odd‐Nitrogen Budget of the Stratosphere

Abstract

The Middle Atmosphere Nitrogen TRend Assessment (MANTRA) series of high‐altitude balloon flights is being undertaken to investigate changes in the concentrations of northern hemisphere mid‐latitude stratospheric ozone, and of nitrogen and chlorine compounds that play a role in ozone chemistry. Four campaigns have been carried out to date, all from Vanscoy, Saskatchewan, Canada (52°01'N, 107°02'W, 511.0 m). The first MANTRA mission took place in August 1998, with the balloon flight on 24 August 1998 being the first Canadian launch of a large high‐altitude balloon in about fifteen years. The balloon carried a payload of instruments to measure atmospheric composition, and made measurements from a float altitude of 32–38 km for one day. Three of these instruments had been flown on the Stratoprobe flights of the Atmospheric Environment Service (now the Meteorological Service of Canada) in the 1970s and early 1980s, providing a link to historical data predating the onset of mid‐latitude ozone loss.

The primary measurements obtained from the balloon‐borne instruments were vertical profiles of ozone, NO₂, HNO₃, HCl, CFC‐11, CFC‐12, N₂O, CH₄, temperature, and aerosol backscatter. Total column measurements of ozone, NO₂, SO₂, and aerosol optical depth were made by three ground‐based spectrometers deployed during the campaign. Regular ozonesonde and radiosonde launches were also conducted during the two weeks prior to the main launch in order to characterize the local atmospheric conditions (winds, pressure, temperature, humidity) in the vicinity of the primary balloon flight. The data have been compared with the Model for Evaluating oZONe Trends (MEZON) chemical transport model, the University of California at Irvine photochemical box model, and the Canadian Middle Atmosphere Model (CMAM) to test our current understanding of model photochemistry and mid‐latitude species correlations. This paper provides an overview of the MANTRA 1998 mission, and serves as an introduction to the accompanying papers in this issue of Atmosphere‐Ocean that describe specific aspects and results of this campaign.     

Spectral investigation of the diffuse-to-direct solar beam irradiances ratio (UV–VIS) in the urban Athens atmosphere

This study explores the influence of air gaseous pollutants–aerosols and solar zenith angle (SZA) on the spectral diffuse-to-direct beam E _dλ/E _bλ irradiances ratio. It does so using ground-based spectroradiometric measurements taken over the Athens atmosphere during May 1995. It was found that the spectral E _dλ/E _bλ ratio decreases rapidly with increasing wavelength and regression curves of the form E _dλ/E _bλ = aλ^?b fitted the experimental data. These curves are strongly modified by aerosols–air pollutants, aerosol optical properties, and SZA. The log–log plot of E _dλ/E _bλ versus λ reveals a significant departure from linearity, which is likely to be associated with aerosol physical properties and SZA effects. The effect of atmospheric turbidity, as expressed through the aerosol optical at 500 nm and SZA on the spectral E _dλ/E _bλ ratio, is investigated in detail for two discernible atmospheric conditions observed in the urban Athens atmosphere. The first case includes different atmospheric turbidity levels under the same SZA, while the second corresponds to different SZA values under the same turbidity levels. It was found that the correlation between E _dλ/E _bλ and spectral aerosol optical depth can be a useful tool in determining the aerosol optical properties and aerosol types composition.     

Analysis and trends of atmospheric turbidity parameters over Cairo

Summary This work deals with the Linke turbidity factor, based on total spectrum observations of the direct solar beam and aerosol turbidity parametersa _a , , and based on observations in broad spectral bands. Diurnal and seasonal variations of these turbidity parameters were analyzed for the period 1975 to 1991.Annual variations of these parameters show low values in winter and high values in both spring and summer. The extinction coefficients decrease with increase of both wavelength and optical airmass. Trend analysis shows an increase in aerosol extinction coefficient below 0.63 m, and a slight decrease for longer wave-lengths.Linear regression relations are also constructed to estimate botha _a and whenT _L is available. The relations show thata _a can be estimated with errors below 20%. The relation with the parameter, may give better results when it is estimated by assigning a fixed value of .Nomenclature AV Monthly and total average of the measured parameter - a Atmospheric optical thicknes - a _a Aerosol optical thickness - a _r Mean value of optical thickness of. Rayleigh atmosphere over all wavelengths - a _o Ozone optical thickness - a _o Ozone absorption coefficient - a _w Water vapor optical thickness - COR Correlation coefficient of the linear relation in percentage - Ex₁, Ex₂, Ex₃ Aerosol extinction coefficients in the bands .2–.53, .53–.63, .63–.695, respectively - I _(o) Normal incident direct solar radiation, under clear sky condition - I _o Extraterrestrial insolation at normal incidence - m _r Relative (optical) air mass - NO Number of the observations used in either making the relation or the verification - RMSE Root mean square error of the linear relation - RMSE% Percentage value of the root mean square error relative to the average measured value AV - T _L Linke turbidity factor - T Dry bulb temperature in °C - u _o Ozone layer thickness, cm - Z Zenith angle - Ångström wavelength exponent - Ångström turbidity coefficient - Wavelength - Y The year number after 1975 With 5 Figures     

Aircraft estimates of the geostrophic drag coefficient and the rossby similarity functions A and B over the sea

Estimates of the geostrophic drag coefficient and the Rossby similarity functions, A and B obtained from data collected by an instrumented aircraft over the sea are presented. The average value of the geostrophic drag coefficient is 0.027 and is independent of the geostrophic windspeed. The dependence of the similarity functions A and B on boundary-layer parameters is investigated. The function A is found to depend on baroclinicity parameters, while B depends on the parameter u _*/fh (where u _* is the surface friction velocity, f is the Coriolis parameter, and h is the boundary-layer depth). Using the geostrophic drag coefficient found here and the results of surface drag coefficient studies, a relationship between geostrophic windspeed and surface windspeed is obtained which shows good agreement with empirical data.     

Snow cover validation and sensitivity to CO2 in the UVic ESCM

Abstract

The University of Victoria's (UVic) Earth System Climate model is used to conduct equilibrium atmospheric CO₂ sensitivity experiments over the range 200–1600 ppm in order to explore changes in northern hemisphere snow cover and feedbacks on terrestrial surface air temperature (SAT). Simulations of warmer climates predict a retreat of snow cover over northern continents, in a northeasterly direction. The decline in northern hemisphere global snow mass is estimated to reach 33% at 600 ppm and 54% at 1200 ppm. In the most northerly regions, annual mean snow depth increases for simulations with CO₂ levels higher than present day. The shift in the latitude of maximum snowfall is estimated to be inversely proportional to the CO₂ concentration. The northern hemisphere net shortwave radiation changes are found to be greater over land than over the ocean, suggesting a stronger albedo feedback from changes in terrestrial snow cover than from changes in sea ice. Results also reveal high sensitivity of the snow mass balance under low CO₂ conditions. The amplification feedback (defined as the zonal SAT anomaly caused by doubling CO₂ divided by the equatorial anomaly) is greatest for scenarios with less than 300 ppm, reaching 1.9 at the pole for 250 ppm. The stronger feedback is attributed to the significant albedo changes over land areas. The simulation with 200 ppm triggers continuous accumulation of snow ('glaciation') in regions which, according to paleo‐reconstructions, were covered by ice during the last glacial cycle (the Canadian Arctic, Scandinavia, and the Taymir Peninsula).     

我国东西部地区地气温差的年代际变化特征

利用1960~2006年我国地温、气温逐日4个时次[02:00(北京时间,下同)、08:00、14:00和20:00]的台站观测资料,计算并分析了我国东南、西北地区各季地气温差的年代际变化特征。分析结果表明:我国东南部地区各季地气温差在20世纪70年代末以前,大部分年份偏高,高于平均值,而在20世纪70年代末以后,我国东南部地区各季地气温差偏低,在夏季和冬季表现尤为明显。我国西北地区春季和夏季地气温差在20世纪70年代末以前大部分年份偏低,低于平均值;而在20世纪70年代末以后,地气温差则大部分年份明显偏高。我国西北地区秋季地气温差的年代际变化特征不明显,而冬季地气温差的年代际变化趋势与春夏季相反,在20世纪70年代末以前大部分年份偏高,高于平均值,而在20世纪70年代末以后偏低。另外,发现地温和气温对我国东南、西北地区各季地气温差的年代际变化在各季所起的贡献作用不同。     

Nephelometer derived and directly measured aerosol optical depth of the atmospheric boundary layer

The aerosol optical depth of the atmospheric boundary layer was determined both from direct solar irradiance measurements and from vertical extrapolation of ground-based nephelometry, during a period with cloudless skies and high aerosol mass loadings in the Netherlands. The vertical profile of the aerosol was obtained from lidar measurements. From humidity controlled nephelometry at the ground and humidity profiles from soundings, the scattering aerosol extinction as a function of height was assessed. Integration of the extinction over the aerosol layer gave the aerosol optical depth of the atmospheric boundary layer. This optical depth at the narrow band of the nephelometer was translated to a spectrally integrated value, assuming an Angstrom wavelength exponent of 1.5, a typical value for The Netherlands.It was found that scattering by the boundary layer aerosol contributed on average 80% to the total atmospheric aerosol optical depth. The uncertainty in this value is estimated to be of the order of 13%. Ammonium nitrate dominated the light scattering. This is an anthropogenic aerosol component.The radiative forcing caused by the light scattering of the anthropogenic aerosol was calculated assuming an upward scattered fraction of 0.3. An average value of − 12 W m ⁻² was found (with an estimated uncertainty of 20%). This corresponds to an absolute increase in the planetary albedo of 0.03, which is equivalent to a 15% increase in the local planetary albedo of 0.2.     

Brewer spectrophotometer total ozone measurements made during the 1998 Middle Atmosphere Nitrogen Trend Assessment (MANTRA) campaign

Abstract

Column ozone data collected using a Brewer spectrophotometer at Vanscoy, Saskatchewan during the Middle Atmosphere Nitrogen Trend Assessment (MANTRA) balloon campaign (Strong, this issue) were reduced using an improved analysis algorithm. The retrieved total ozone values are compared with those from other instruments and good agreement was found. The aerosol optical depth has also been calculated using the same set of data and the results are presented. Periods of an increased aerosol optical depth coincide with periods when plumes of smoke from nearby forest fires reached the campaign site.     

A numerical model for one‐dimensional simulation of stratospheric chemistry

Abstract

We describe a one‐dimensional (1‐D) numerical model developed to simulate the chemistry of minor constituents in the stratosphere. The model incorporates most of the chemical species presently found in the upper atmosphere and has been used to investigate the effect of increasing chlorofluorocarbon (CFC) emissions on ozone (O₃).

Our calculations confirm previous results that O₃ depletions in the 20–25 km region, the region of the O₃ maximum, are very sensitive to the relative abundances of Cl_x and NO_y in the lower stratosphere for high Cl_x amounts. The individual abundances of lower stratospheric Cl_x and NO_y amounts are very sensitive to upper tropospheric mixing ratios, which, in turn, are determined largely by surface input fluxes and heterogeneous loss processes. Thus the behaviour of column O₃ depletions at high Cl_x levels is greatly affected, albeit indirectly, by tropospheric processes. For high Cl_x levels the O_x flux from the stratosphere to the troposphere is dramatically reduced, leading to a large reduction in tropospheric O₃. Some of the variation between different published 1‐D model results is most likely due to this critical dependence of O₃ depletion on NO_y‐Cl_x ratios.

Model simulations of time‐dependent CFC effects on ozone indicate that if CFCs were to remain at constant 1980 emission rates while N₂O increased at 0.25% a^?1 and CH₄ increased at 1% a^?1, we could expect a 2.2% decrease in total column O₃ (relative to the 1980 atmosphere) by the year 2000. However, if CFC emission rates were to increase by 3% a^?1 (current estimates are 5–6% a^?1), we would predict a depletion of 2.7% by the year 2000. The calculations for times beyond the year 2000 suggest that the effects on total O₃ will begin to accelerate. If methyl chloroform emissions are added at 7% a^?1 (current estimates are 7–9% a^?1) to the above CFC‐N₂O‐CH₄ scenario we calculate total O₃ depletions by the year 2000 that are 41% larger than those calculated without. This suggests that if the emissions of methyl chloroform continue to increase at their present rate then methyl chloroform could have a significant effect upon total O₃.     

A comparison between two stochastic diffusion models in a complex three-dimensional flow

A Random Displacement Model (RDM) and a Langevin Equation Model (LEM) are used to simulate point releases in a complex flow around a building. The flow field is generated by a three-dimensional finite element model that uses the standardk- model to parameterize the turbulence. The RDM- and LEM-calculated concentration fields are compared, with particular emphasis on the structure in regions with high turbulence and/or recirculation. RDM and LEM results are similar qualitatively, but RDM tends to predict lower concentration levels. In part this is due to the higher early-time diffusion. However, the expected convergence at later times is prevented by the interaction of the diffusion with the strongly inhomogeneous mean flow.Notation a _i coefficient in the Langevin equation - b _ij coefficient in the Langevin equation - C ₀ the universal constant associated with the Lagrangian structure function - H building height (22.5 m) - K eddy viscosity - K _k eddy viscosity used in the definition of the off-diagonal Reynolds stresses - k turbulent kinetic energy - LEM Langevin Equation Model - p ₁ local unit vector in thexy-plane, orthogonal tos - p ₂ local unit vector, orthogonal to boths andp ₁ - RDM Random Displacement Model - s local unit vector in the streamline direction - T local decorrelation time (Lagrangian time scale) - U magnitude of the local Eulerian mean wind velocity - u _s total velocity in the streamline direction - u ₁ velocity component in thexy-plane, orthogonal to the streamline direction - u ₂ velocity component orthogonal to bothu _s andu ₁ - _i mean Eulerian wind velocity - W _i stochastic vector-valued Wiener process - x unit vector inx-direction - y unit vector iny-direction - z unit vector inz-direction - angle between thexy-plane and the mean wind streamline - angle between the projection in thexy-plane of the streamline and thex-axis - _ij the Kronecker delta function - rate of turbulence dissipation - _i/g_a the part ofa _i that contains mean wind and turbulence gradients - _ij inverse of a Reynolds stress tensor component - _ij shorthand for a quantity that defines a part of _i/g_a - _i shorthand for a quantity that defines a part of _i/g_a - _ij Reynolds stress tensor component     

东亚500hpa月平均高度场的切比雪夫系数与南方涛动的耦合振荡关系

气象要素场通常可以通过多种方法,如经验正交函数,切比雪夫正交多项式等,分解成若干典型气象要素场。后者已由规则格点推广到不规则格点[1]。张家诚[2]、陈玉琼[3]等先后探讨了长江中下游降水和温度与东亚500hPa月平均高度场的切比雪夫正交多项式系数（以下简称为切比雪夫系数）的关系,作者也分析了我国西北地区夏季干、湿状况与东亚经向环流指数（A₁₀）之间的联系[4]。但是,就东亚500hPa月平均高度场切比雪夫系数本身气候振荡的研究仍涉及不多。而这一方面的研究对于加深了解我国大范围的气候异常是有益的。      

Henry's law and the behavior of weak acids and bases in fog and cloud

Experimental data from two field experiments on ground based clouds were used to study the distribution of formic acid, acetic acid, ammonia and S(IV) species between liquid and gas phase. The ratio of the concentrations of these compounds between the phases during concurrent measurements was compared to ratios expected according to Henry's law (considering the pH influence). Large discrepancies of several orders of magnitude were seen. Three hypotheses have been investigated to explain the observed discrepancies: The existence of a microscale equilibrium which does not persist in a bulk sample, a thermodynamic shift of the equilibrium due to competing reactions, and nonequilibrium conditions due to mass transfer limitations. Approximate quantitative calculations show that none of these hypotheses is sufficient to explain all of the discrepancies, so a combination of different effects seems to be responsible for this observation. The same theoretical considerations also suggest that mass transfer limitation may be an important factor for highly soluble compounds. The data presented here indicates that it is not possible to simply extrapolate interstitial gas phase composition from measured bulk liquid phase concentrations of a fog or cloud.Notation [r _max] liquid phase molar uptake rate (mol l^–1 s^–1) - [A _g ] concentration ofA in gas phase (atm) - [A _l ] concentration ofA in liquid phase (mol l^–1) - [A _g , 0] concentration ofA in gas phase (atm) at time 0 - LWC liquid water content (g m^–3) - R universal gas constant (0.082 l atm mol^–1 K^–1 - D _g diffusivity (for all gases 0.1 cm² s^–1 was used) - K _H ^* effective Henry's law coefficient (mol l^–1 atm^–1) - t _f lifetime of fog droplet (s) - a droplet radius (cm) - accommodation coefficient - R factor of discrepancy - T temperature (K) - v mean molecular speed (cm s^–1) formic acid: 35 000 acetic acid: 31 000 ammonia: 58 000     

Characteristics of the Lyman-alpha humidiometer and measurements of turbulent humidity fluctuations over the ocean

The characteristics of a Lyman-alpha humidiometer have been carefully examined in an air-conditioned test chamber. The results confirm that when carefully used, this humidiometer is suitable for measurements of turbulent humidity fluctuations. Measurements with a Lyman-alpha humidiometer were carried out in the surface boundary layer over the ocean. The relation between turbulent intensity ( _a = a ^ov2) and the friction humidity (a _*) can be expressed as _a = l.6a _*. The spectrum of turbulent humidity for wind speeds larger than 3 m s ^–1 conforms to the similarity law in the surface boundary layer. The spectrum has two characteristic normalized frequencies, namely, a higher peak and a secondary peak (or a shoulder).     

Impacts of future Indian greenhouse gas emission scenarios on projected climate change parameters deduced from MAGICC model

The MAGICC (Model for the Assessment of Greenhouse gas Induced Climate Change) model simulation has been carried out for the 2000–2100 period to investigate the impacts of future Indian greenhouse gas emission scenarios on the atmospheric concentrations of carbon dioxide, methane and nitrous oxide besides other parameters like radiative forcing and temperature. For this purpose, the default global GHG (Greenhouse Gases) inventory was modified by incorporation of Indian GHG emission inventories which have been developed using three different approaches namely (a) Business-As-Usual (BAU) approach, (b) Best Case Scenario (BCS) approach and (c) Economy approach (involving the country’s GDP). The model outputs obtained using these modified GHG inventories are compared with various default model scenarios such as A1B, A2, B1, B2 scenarios of AIM (Asia-Pacific Integrated Model) and P50 scenario (median of 35 scenarios given in MAGICC). The differences in the range of output values for the default case scenarios (i.e., using the GHG inventories built into the model) vis-à-vis modified approach which incorporated India-specific emission inventories for AIM and P50 are quite appreciable for most of the modeled parameters. A reduction of 7% and 9% in global carbon dioxide (CO₂) emissions has been observed respectively for the years 2050 and 2100. Global methane (CH₄) and global nitrous oxide (N₂O) emissions indicate a reduction of 13% and 15% respectively for 2100. Correspondingly, global concentrations of CO₂, CH₄ and N₂O are estimated to reduce by about 4%, 4% and 1% respectively. Radiative forcing of CO₂, CH₄ and N₂O indicate reductions of 6%, 14% and 4% respectively for the year 2100. Global annual mean temperature change (incorporating aerosol effects) gets reduced by 4% in 2100. Global annual mean temperature change reduces by 5% in 2100 when aerosol effects have been excluded. In addition to the above, the Indian contributions in global CO₂, CH₄ and N₂O emissions have also been assessed by India Excluded (IE) scenario. Indian contribution in global CO₂ emissions was observed in the range of 10%–26%, 6%–36% and 10%–38% respectively for BCS, Economy and BAU approaches, for the years 2020, 2050 and 2100 for P50, A1B-AIM, A2-AIM, B1-AIM & B2-AIM scenarios. CH₄ and N₂O emissions indicate about 4%–10% and 2%–3% contributions respectively in the global CH₄ and N₂O emissions for the years 2020, 2050 and 2100. These Indian GHG emissions have significant influence on global GHG concentrations and consequently on climate parameters like RF and ∆T. The study reflects not only the importance of Indian emissions in the global context but also underlines the need of incorporation of country specific GHG emissions in modeling to reduce uncertainties in simulation of climate change parameters.     

Arctic aerosol and Arctic climate: Results from an energy budget model

An energy budget model is used to study the effect on Arctic climate of optically active aerosol in the Arctic atmosphere. The dependence of the change in surface temperature on the vertical distribution of the aerosol and on the radiative properties of the aerosol-free atmosphere, the Arctic surface, and the aerosol, itself, are calculated. An extensive sensitivity analysis is performed to assess the degree to which the results of the model are dependent upon the assumptions underlying it.List of Symbols Used I ₀ Solar flux at the top of the Arctic Atmosphere (Arctic here means 70° N latitude to the pole) - a _S Surface albedo of the Arctic (a _S ^c is the value of surface albedo at which the sign of the surface temperature perturbation changes) - Reflection coefficient of the aerosol-free Arctic atmosphere - Absorption coefficient of the aerosol-free Arctic atmosphere - Transmission coefficient of the aerosol-free Arctic atmosphere - RI ₀ Total flux of sunlight reflected from the Arctic - A _A I ₀ Total flux of sunlight absorbed in the Arctic atmosphere - A _S I ₀ Total flux of sunlight absorbed at the Arctic surface - A _aer I ₀ Total flux of sunlight absorbed in the Arctic aerosol - Q _A Net atmospheric flow of energy, per unit of Arctic surface area, north across 70° N latitude - Q _S Net oceanic flow of energy, per unit of Arctic surface area, north across 70° N latitude - E Convective plus latent heat fluxes from surface to atmosphere - F _A Net flow of energy to the Arctic atmosphere - F _S Net flow of energy to the Arctic surface - T _A An effective temperature of the Arctic atmosphere - T _S Surface temperature of the Arctic - w Single-scattering albedo of the aerosol - t Optical depth of the aerosol - g Fraction of incident radiation scattered forward by the aerosol - Reflection coefficient of the aerosol - Absorption coefficient of the aerosol - Transmission coefficient of the aerosol - p,q Number of atmospheric layers and the inverse of the fraction of incident IR absorbed in each layer in the energy budget model - F,G,H Measures of the amount of IR-active atmosphere above the surface, the aerosol, and the clouds