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1.
Summary ?The dependence of aerosol optical depth on wavelength as well as the fit of the ?ngstr?m approximation have been investigated
under different air masses at a sub-Arctic location (Abisko, Sweden; 68° 21′ N, 18° 49′ E) and a tropical environment (Ife,
Nigeria; 7° 30′ N, 4° 31′ E). The study is based on spectral data acquired with a high resolution spectral radiometer (spectral
range: 300–1100 nm) in absorption-free regions.
The wavelength dependence of the aerosols under different air mass conditions at the sub-arctic location offer significant
contrasts to aerosols of Saharan origin at Ife. A general characteristic of the aerosol optical depth spectra after the Pinatubo
volcanic eruption was a much weaker wavelength dependence relative to pre-Pinatubo conditions.
Categorising the features of the optical depth spectra according to their wavelength dependence, three main groups were observed
at Abisko, while two main classes have been discussed for the harmattan season in the tropical climate of Ife and environs.
For the first two groups in Abisko (and the first group at Ife), aerosol optical depth generally decreased with wavelength
while the third group (second group at Ife) exhibited strong curvatures.
The correlation coefficient obtained from the regression equation of the ?ngstr?m equation, has been shown to be a good index
of the general fit of the ?ngstr?m approximation for the three groups at Abisko, but much weaker for the harmattan conditions
at the tropical location. Although the probability of systematic deviations from the ?ngstr?m law is highest under intense
harmattan conditions with considerably high β and low α, it has been observed that the ?ngstr?m fit was good in many highly
turbid conditions at the tropical site. Hence, apart from the level of turbidity, the applicability of the ?ngstr?m approximation
is strongly dependent on aerosol characteristics and source region.
Formerly Adeyefa.
Received May 18, 2001; revised June 20, 2002; accepted August 5, 2002 相似文献
2.
Height, time, and latitude dependences are analyzed of zonal mean vertical component of wind velocity for the period of 1992–2006
from the UKMO atmospheric general circulation model. It is shown that the ascending wind speed can provide vertical transport,
against gravity, of rather large (up to 3–5μm) aerosol particles with density to 1.0–1.5 g/cm3 in the stratosphere and mesosphere. The wind velocity vertical component is supposedly a significant factor of particle motion
up to 30–40–km levels and can affect sedimentation rate and residence time of the aerosol particles in the stratosphere. Structure
of the mean vertical component of wind velocity allows occurrence of dynamically stable aerosol layers in the middle stratosphere. 相似文献
3.
S. P. Smyshlyaev P. A. Blakitnaya M. A. Motsakov 《Russian Meteorology and Hydrology》2020,45(3):153-160
The variability of Antarctic total column ozone
in 1980–2018 is considered. The study analyzes trends in Antarctic total
column ozone during the study period as well as the physical and
chemical processes affecting the seasonal variability of total column
ozone. The main attention is paid to the influence of dynamical
processes on the stability of the Antarctic polar vortex, to the
formation of polar stratospheric clouds, and to the influence of
gas-phase and heterogeneous processes on the surface of polar
stratospheric clouds and sulfate aerosol. The method of research is the
analysis of the results of ground and satellite observations and
numerical modeling of physical and chemical processes over the Antarctic
using a global chemistry transport model with the dynamical parameters
specified from reanalysis data. 相似文献
4.
Ellsworth G. Dutton John J. DeLuisi Gary Herbert 《Journal of Atmospheric Chemistry》1989,9(1-3):71-79
Measurements of spectral aerosol optical depth in the Alaskan and Canadian Arctic were made from the NOAA Lockheed WP-3D aircraft as part of the second Arctic Gas and Aerosol Sampling Program (AGASP-II) during April 1986. The flight tracks and altitudes flown enabled measurements of the vertical and horizontal distribution of aerosol optical depth in the troposphere as well as direct determination of the stratospheric component. Tropospheric aerosol optical depth ranged from about 0.1 to 0.7. The factor of 7 variability sometimes occurred within 50 km horizontally; comparable variability occurred within less than 1 to 2 km vertically. The Angstrom exponents of the spectral optical depths ranged from 0.5 to 2.0, and some of the variability was apparently related to distinct aerosol regimes. 相似文献
5.
Using the monthly mean NCEP/NCAR reanalysis dataset, the three-dimensional Eliassen-Palm (EP) fluxes of quasi-stationary wave
propagation in the lower stratosphere were computed for each month from November to March for the period from 1958 to 2007.
It is shown that the upward planetary wave propagation from the troposphere to the stratosphere generally occurs over the
northern Eurasia, while their weak downward propagation is observed in Labrador and southern Greenland regions in the lower
stratosphere. Interannual variations of the vertical EP fluxes also have the dipole-like spatial pattern with the opposite
anomalies in the West and East hemispheres which are most prominent in January–February. Significant differences in the interaction
of the zonal circulation of the stratosphere in the beginning of winter (November–December) and mid-to-late winter (January–March)
are revealed. Intensification of the planetary waves’ penetration into the stratosphere in December causes changes in the
stratospheric dynamics, creating the “preconditions” for the stratospheric warming appearances in January, but such a mechanism
is not detected in February. In the years with the cold polar vortex, the “stratospheric bridge” is formed with the strengthening
of the upward EP flux over the northern Eurasia and downward EP flux over the North Atlantic. 相似文献
6.
An Empirical Method for Estimating Background Stratospheric Aerosol Extinction Profiles over China
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YANG Jing-Mei 《大气和海洋科学快报》2012,5(2):95-101
The current paper introduces an empirical method for estimating the vertical distribution of background stratospheric aerosol extinction profiles covering the latitude bands of 50±5°N,40±5°N,30±5°N,and 20±5°N and the longitude range of 75 135°E based on Stratospheric Aerosol and Gas Experiment (SAGE) II aerosol extinction measurements at wavelengths of 1020 nm,525 nm,452 nm,and 386 nm for the volcanically calm years between 1998 2004.With this method,the vertical distribution of stratospheric aerosol extinction coefficients can be estimated according to latitude and wavelength.Comparisons of the empirically calculated aerosol extinction profiles and the SAGE II aerosol measurements show that the empirically calculated aerosol extinction coefficients are consistent with SAGE II values,with relative differences within 10% from 2 km above the tropopause to 33 km,and within 22% from 33 km to 35 km.The empirically calculated aerosol stratospheric optical depths (vertically integrated aerosol extinction coefficient) at the four wavelengths are also consistent with the corresponding SAGE II optical depth measurements,with differences within 2.2% in the altitude range from 2 km above the tropopause to 35 km. 相似文献
7.
Nikolay Kolev Ivan Grigorov Ivan Kolev P. C. S. Devara P. Ernest. Raj K. K. Dani 《Boundary-Layer Meteorology》2007,124(1):99-115
We present measurements of the vertical aerosol structure and the aerosol optical depth in the lower troposphere performed
above the city of Sofia (an urban area situated in a mountain valley), western Bulgaria by means of a ground-based aerosol
lidar operating continuously for a number of years. The lidar measurements were accompanied by measurements of the aerosol
optical depth (AOD) in the visible and near infrared regions of the spectrum performed in October 2004 using Microtops II
radiometers. The maximum values of the AOD were found to occur 1–2 h before the complete development of the atmospheric boundary
layer, i.e. during the residual layer destruction, which confirms our hypothesis concerning the slope circulation effect on
the processes taking place in the atmospheric boundary layer. The AOD values obtained by the lidar are lower than those taken
by the sun photometer. Further, the AOD exhibits two different types of behaviour. In the case of a ‘clear atmosphere’ (i.e.
in the absence of volcanic eruptions and/or dust transport from the Sahara) most of the aerosol accumulated within the atmospheric
boundary layer over the urban area considered. The combined use of the two instruments allows the comparison between the optical
characteristics of the atmospheric aerosol (e.g. aerosol extinction coefficient, etc.) obtained by the lidar and through an
independent method (sun photometer). 相似文献
8.
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. 相似文献
9.
Snow/Rainfall Anomaly in Winter of Northern China and Associated Atmospheric Circulation and Aerosol Distribution Features
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Based on the NCEP/NCAR reanalysis data,China station precipitation data from 1960 to 2008,and aerosol optical depth (AOD) data in northern China from 1980 to 2004,this paper investigates the variability of winter snow/rainfall in northern China and the associated atmospheric circulation and aerosol distribution characteristics by using composite analysis.The results show that winter precipitation in northern China has been generally increasing since the 1960s.Among the winters of 1990-2008,the years with more rain/snow (MRSYs) are 1998,2003,and 2006,while the years with less rain/snow (LRSYs) are 2005,1997,and 2001.Composite analysis finds that the main differences of atmospheric circulation in East Asia between MRSYs and LRSYs are as follows.1) In MRSYs,strong low-level cold air over the northern polar region and Taymyr Peninsula migrates southward to northern China (Northwest,North,and Northeast China),establishing a channel favoring continuous southward transport of cold air.In LRSYs,however,this cold air channel does not exist.2) In MRSYs,the frontal zone and westerlies are over North China,and the low-level geopotential height field from eastern China to West Pacific exhibits an "east high,west low" pattern,which is conducive to easterly and southerly airflows moving northward along 110 E.In LRSYs,the 500-hPa prevailing westerly winds stay far away from China and the low-level southeasterlies move to higher latitudes,which are disadvantageous to the development of precipitation in northern China.3) In MRSYs,large-scale upward motions combined with local-scale updrafts develop into strong slanted climbing airflows,forming a vertical circulation that favors the generation of heavy snows in eastern China.In LRSYs,the vertical circulation moves eastward into the Pacific Ocean.Furthermore,the correlation analysis on AOD and winter precipitation during the period 1980-2004 in northern China reveals that AOD differs significantly between MRSYs and LRSYs and the annual variation of winter rain/snow is positively correlated to the annual variation of AOD with a correlation coefficient of 0.415 at the 0.001 significance level. 相似文献
10.
Using measures of wind strength and direction taken onboard ships during the 1750–1850 (CLIWOC project) period, preliminary
reconstructions are attempted for the North Atlantic Oscillation (NAO) and the Southern Oscillation Index (SOI). The reconstructions
are based on regression equations developed using similar data from the ICOADS dataset. Although the regression relationships
developed over a calibration period (1881–1940) work almost as well over an independent verification period (1941–1997), application
to the earlier 1750–1850 period results in barely statistically significant correlation coefficients when compared with a
number of other NAO and SOI reconstructions from other proxy and long instrumental sources. A number of possibilities are
investigated to attempt to determine the cause, the most likely of which is that the number of observations available for
the CLIWOC period is just too low in some regions. As large numbers of ships' logbooks remain to be digitised, the regression
relationships will prove useful to focus effort in future digitisation endeavours. 相似文献
11.
I. P. Parshutkina E. V. Sosnikova N. P. Grishina E. A. Stulov N. O. Plaude N. A. Monakhova 《Russian Meteorology and Hydrology》2011,36(6):355-361
Daily measurements of atmospheric aerosol characteristics were carried out in Dolgoprudny (Moscow region) in June–August 2010.
The particle concentrations at 11 size gradations within the range of 0.01–10 μm and the concentrations of cloud condensation
nuclei active at water vapor supersaturation of 0.2–1% were determined. It is shown that the long anticyclonic conditions
and the burning of forests and peat bogs resulted in the increase in total aerosol concentration in surface air by more than
1.5 times and in concentrations of particles with the diameter of 0.1–1 μm and > 1 μm by 5 and 10 times, respectively. The
fire smoke mainly consisted of the particles with the size of 0.1–3 μm. The particles with the size of more than 5 μm were
not observed. The recurrent visibility decrease up to hundreds of meters was caused by the increase in the concentration of
particles with the diameter of more than 0.32μm in the air. During the smoke blanketing, the concentration of active condensation
nuclei in aerosol increased almost by 20 times that created an opportunity for watering of aerosol particles and formation
of the acid smog. 相似文献
12.
J. Räisänen 《Theoretical and Applied Climatology》1999,64(1-2):1-13
Summary The qualitative agreement of two climate models, HADCM2 and ECHAM3, on the response of surface climate to anthropogenic climate
forcing in the period 2020 – 2049 is studied. Special attention is paid to the role of internal climate variability as a source
of intermodel disagreement. After illustrating the methods in an intermodel comparison of simulated changes in June–August
mean precipitation, some global statistics are presented. Excluding surface air temperature, the four-season mean proportion
of areas in which the two models agree on the sign of the climatic response is only 53 – 60% both for increases in CO2 alone and for increases in CO2 together with direct radiative forcing by sulphate aerosols, but somewhat larger, 59 – 70% for the separate aerosol effect.
In areas where the response is strong (at least twice the standard error associated with internal variability) in both models,
the agreement is better and the contrast between the different forcings becomes more marked. The proportion of agreement in
such areas is 57 – 75% for the response to increases in CO2 alone, 64 – 84% for the response to combined CO2 and aerosol forcing, and as high as 88 – 94% for the separate aerosol effect. The relatively good intermodel agreement for
aerosol-induced climate changes is suggested to be associated with the uneven horizontal distribution of aerosol forcing.
Received December 2, 1998 Revised May 5, 1999 相似文献
13.
This study presents the monthly climatology and variability of the historical soviet snow depth data. This data set was developed
under the bilateral data exchange agreement between United States of America and the former Union of Soviet Socialist Republics.
The original data is for 284 stations for periods varying from 1881 upto 1985. The seasonal cycle of the mean snow depth has
been presented both as spatial maps and as averages over key locations. The deepest snow (=80 cms/day) areas are found over
Siberia (in Particular over 80′–100 ′E, 55′–70 ′N) during March. Over the course of the annual cycle average snow depth over
this region changes dramatically from about 10 cms in October to about 80 cms in March. The variability is presented in the
form of spatial maps of standard deviation. To investigate the interaction of snow depth with Indian monsoon rainfall (IMR),
lag and lead correlation coefficients are computed. Results reveal that the winter-time snow depth over western Eurasia surrounding
Moscow (eastern Eurasia in central Siberia) shows significant negative (positive) relationship with subsequent IMR. Following
the monsoon the signs of relationship reverse over both the regions. This correlation structure is indicative of a midlatitude
longwave pattern with an anomalous ridge (trough) over Asia during the winter prior to a strong (weak) monsoon. As the time
progresses from winter to spring, the coherent areas of significant relationship show southeastward propagation. Empirical
orthogonal function analysis of the snow depth reveal that the first mode describes a dipole-type structure with one centre
around Moscow and the other over central Siberia, depicting similar pattern as the spatial correlation structure. The decadal-scale
IMR variations seem to be more associated with the Northern Hemisphere midlatitude snow depth variations rather than with
the tropical ENSO (El Nino Southern Oscillation) variability.
Received: 16 March 1998 / Accepted: 24 December 1998 相似文献
14.
Summary This study investigated the impact of atmospheric aerosols on surface ultraviolet (UV) irradiance at Gwangju, Korea (35°13′N,
126°50′E). Data analyzed included surface UV irradiance measured by UV radiometers from June 1998 to April 2001 and the aerosol
optical depth (AOD) in the visible range determined from a rotating shadow-band radiometer (RSR). The radiation amplification
factor (RAF) of ozone for UV-B (280–315 nm) at Gwangju was 1.32–1.62. Values of the RAF of aerosols (RAFAOD) for UV-A and UV-B were 0.18–0.20 and 0.22–0.26, respectively.
Authors’ addresses: Jeong Eun Kim, Advanced Environmental Monitoring Research Center (ADEMRC), Gwangju Institute of Science
and Technology (GIST) and Korea Meteorological Administration (KMA); Seong Yoon Ryu, Advanced Environmental Monitoring Research
Center (ADEMRC), Gwangju Institute of Science and Technology (GIST) and Division of Metrology, Korea Research Institute of
Standards and Science (KRISS); Young Joon Kim, Advanced Environmental Monitoring Research Center (ADEMRC) Gwangju Institute
of Science and Technology (GIST), 1 Oryong-dong, Buk-gu, Gwangju 500-712, Republic of Korea. 相似文献
15.
Stratospheric zonal wind and temperature in relation to summer monsoon rainfall over India 总被引:1,自引:0,他引:1
Summary The interannual variability of the Indian summer monsoon (June–September) rainfall is examined in relation to the stratospheric
zonal wind and temperature fluctuations at three stations, widely spaced apart. The data analyzed are for Balboa, Ascension
and Singapore, equatorial stations using recent period (1964–1994) data, at each of the 10, 30 and 50 hPa levels. The 10 hPa
zonal wind for Balboa and Ascension during January and the 30 hPa zonal wind for Balboa during April are found to be positively
correlated with the subsequent Indian summer monsoon rainfall, whereas the temperature at 10 hPa for Ascension during May
is negatively correlated with Indian summer monsoon rainfall. The relationship with stratospheric temperatures appears to
be the best, and is found to be stable over the period of analysis.
Stratospheric temperature is also significantly correlated with the summer monsoon rainfall over a large and coherent region,
in the north-west of India. Thus, the 10 hPa temperature for Ascension in May appears to be useful for forecasting summer
monsoon rainfall for not only the whole of India, but also for a smaller region lying to the north-west of India.
Received July 30, 1999 Revised March 17, 2000 相似文献
16.
N. O. Plaude E. A. Stulov I. P. Parshutkina E. V. Sosnikova N. A. Monakhova V. V. Yakhno 《Russian Meteorology and Hydrology》2012,37(1):21-27
The seasonal variations of the concentration of particles of different sizes in the atmospheric surface layer are studied
on the basis of the data of daily measurements of atmospheric aerosol characteristics in the town of Dolgoprudny (20 km from
the center of Moscow) carried out in 2006–2009. It is revealed that the steady variations of monthly mean aerosol concentration
are observed within the particle diameter interval of 0.02–1 μm. The annual course of concentration of these particles has
two maxima, in February-March and in September–October, and one minimum in June. The concentrations of particles with the
size of 0.01–0.02 μm defined by the general atmospheric background and the concentrations of particles of >1 μm associated
with the local sources do not have clearly pronounced seasonal variations. It is shown that the regularities of the annual
concentration variations of particles with the size of 0.02–1 μm are mainly explained by the sign and value of the lapse rate
in the layer up to 925 hPa that indicates the prevalence of the vertical mixing in the processes of aerosol scattering in
the surface layer as compared with the horizontal transfer. 相似文献
17.
Spatio-temporal variations of water vapor optical depth in the lower troposphere (450-3850 m) over Pune (18o32’N, 73o51’E, 559 m Above Mean Sea Level), India have been studied over a period of five years. The mean ver-tical structure showed that the moisture content is greatest at the lowest level and decreases with increasing altitude, except in the south-west monsoon season (June to September) when an increase upto 950 m has been found. Optical depths are maximum in the monsoon season. The increase from pre-monsoon (March-May) to monsoon season in moisture content on an average is by about 58% in the above altitude range. The temporal variations in surface Rela-tive Humidity and optical depth at 450 m show positive correlation. The amplitude of seasonal oscillation is the larg-est at 1465 m altitude. The time-height cross-sections of water vapor optical depths in the lower troposphere showed a contrast between years of good and bad monsoon. 相似文献
18.
《Atmospheric Research》2008,87(3-4):194-206
This work aims at determining the aerosol particle radii in the atmosphere of Athens. Such a work is carried out in Athens for the first time. For this purpose, solar spectral direct-beam irradiance measurements were used in the spectral range 310–575 nm. To estimate the particle radius from aerosol optical depth retrieval, a minimization technique was employed based on the golden-section search of the difference between experimental and theoretical values of the aerosol optical depth. The necessary Mie computations were performed based on the algorithm LVEC.In this study, the mean particle radius of a given distribution was calculated every 30 min during cloudless days in the period November 1996 to September 1997. The largest particles were observed in the summer and the smallest during winter. The result was verified by the increased values of the aerosol optical depth and the turbidity factors calculated in the summer. The differences in the diurnal variation from season to season are attributed to the prevailing wind regime, pollutant emission and sink rates in the atmosphere of Athens. 相似文献
19.
Ice samples from the 905 m deep Dome C core (East Antarctica) were studied in terms of insoluble microparticle contents. Various
techniques were used: right angle light scattering, nephelometer (multiangle light scattering), Coulter counter and microscope
analyses, in order to make a thorough study of the physical and optical properties of microparticles and their variations
over the last 30000 years. Because of the possible effect of atmospheric turbidity on the earth-atmosphere radiation balance,
optical parameters of climatic importance were estimated for insoluble microparticles.
The detailed profile of total microparticle mass concentrations shows a drastic (factor of 17 ± 13) difference between high
Last Glacial Maximum (LGM) and low Holocene concentrations. The optical scattering properties of 18000 BP continental dust
do not indicate a significant difference with respect to Holocene dust in terms of particle size distribution and complex
refractive index. The number to log radius size distribution of microparticles for the entire 30 000 yr period can be fitted
by a log-normal distribution with two parameters (modal radius 0.25 ± 0.08 μm; geometric standard deviation 2.2. ± 0.2). However,
for the smallest particles a better adjustment between experimental and theoretical scattering diagrams is obtained by adding
to the observed size distribution another log-normal distribution (modal radius = 0.025 μm, σ
g
= 2). The complex refractive index is 1.53 to 1.56 for the real part and 0.005 ± 0.005 for the imaginary part at the wavelength
used (λ= 546 nm).
During the LGM stage, over the whole of Antarctica, the change in the total optical depth due to the drastic change in the
insoluble aerosol loading is small because insoluble impurities are not the dominant aerosol component. It may have produced
a slight warming of the snow surface (≈ 2 K). In the dust source regions, the optical depth would have been a maximum of 2
to 4 times the present value. The possible warming of the atmosphere in these regions is estimated at 3 K per day and should
therefore be taken into account in paleoclimate reconstruction models. 相似文献
20.
A.D. Adamopoulos H.D. Kambezidis D.G. Kaskaoutis G. Giavis 《Atmospheric Research》2007,86(3-4):194-206
This work aims at determining the aerosol particle radii in the atmosphere of Athens. Such a work is carried out in Athens for the first time. For this purpose, solar spectral direct-beam irradiance measurements were used in the spectral range 310–575 nm. To estimate the particle radius from aerosol optical depth retrieval, a minimization technique was employed based on the golden-section search of the difference between experimental and theoretical values of the aerosol optical depth. The necessary Mie computations were performed based on the algorithm LVEC.In this study, the mean particle radius of a given distribution was calculated every 30 min during cloudless days in the period November 1996 to September 1997. The largest particles were observed in the summer and the smallest during winter. The result was verified by the increased values of the aerosol optical depth and the turbidity factors calculated in the summer. The differences in the diurnal variation from season to season are attributed to the prevailing wind regime, pollutant emission and sink rates in the atmosphere of Athens. 相似文献