Atmospheric circulation controls on precipitation isotope–climate relations in western Canada     

By S. J. BIRKS  T. W. D. EDWARDS 《Tellus. Series B, Chemical and physical meteorology》2009,61(3):566-576

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Retrieval of aerosol optical thickness for desert conditions using MERIS observations during the SAMUM campaign     

By TILMAN DINTER  WOLFGANG VON HOYNINGEN-HUENE  JOHN P. BURROWS  ALEXANDER KOKHANOVSKY  EIKE BIERWIRTH  MANFRED WENDISCH  DETLEF MÜLLER  RALPH KAHN  MOHAMMED DIOURI 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):229-238

Approximately 30% of the land surface is arid, having desert or semi-desert conditions. Aerosol originating from these regions plays a significant role in climate and atmospheric chemistry of the atmosphere. Retrieving aerosol properties from space-borne platforms above desert conditions, where the surface reflectance is usually very bright, is a challenging task. The proportion of the surface to top of atmosphere (TOA) reflectance can reach values over 90%, especially for wavelength above 500 nm. For these reasons detailed knowledge of aerosol and surface optical properties from these regions is required to separate atmosphere from intrinsically bright surfaces.
An approach to retrieve aerosol properties over arid and semi-arid regions based on the Bremen Aerosol Retrieval (BAER) has been developed and validated within the Dust Aerosol Retrievals from Space-Born Instruments (DREAMS) Project, which is part of the Saharan Mineral Dust Experiment ( SAMUM, 2006 ). Combining measurements of the backscattered radiation from the Medium Resolution Imaging Spectrometer (MERIS) instrument aboard Environmental Satellite (ENVISAT) and ground-based measurements in Morocco in radiation closure experiments yields the aerosol optical properties of mineral dust at selected locations.  相似文献   

Exploring CO pollution episodes observed at Rishiri Island by chemical weather simulations and AIRS satellite measurements: long-range transport of burning plumes and implications for emissions inventories     

By HIROSHI TANIMOTO  KEIICHI SATO  TIM BUTLER  MARK G. LAWRENCE  JENNY A. FISHER  MONIKA KOPACZ  ROBERT M. YANTOSCA  YUGO KANAYA  SHUNGO KATO  TOMOAKI OKUDA  SHIGERU TANAKA  JIYE ZENG 《Tellus. Series B, Chemical and physical meteorology》2009,61(2):394-407

The summer of 2003 was an active forest fire season in Siberia. Several events of elevated carbon monoxide (CO) were observed at Rishiri Island in northern Japan during an intensive field campaign in September 2003. A simulation with a global chemistry-transport model is able to reproduce the general features of the baseline levels and variability in the observed CO, and a source attribution for CO in the model suggests that the contribution from North Asia dominated, accounting for approximately 50% on average, with contributions of 7% from North America and 8% from Europe and 30% from oxidation of hydrocarbons. With consideration of recent emission estimates for East Asian fossil fuel and Siberian biomass burning sources, the model captures the timing and magnitude of the CO enhancements in two pollution episodes well (17 and 24 September). However, it significantly underestimates the amplitude during another episode (11–13 September), requiring additional CO emissions for this event. Daily satellite images from AIRS reveal CO plumes transported from western Siberia toward northern Japan. These results suggest that CO emissions from biomass burning in western Siberia in 2003 are likely underestimated in the inventory and further highlight large uncertainties in estimating trace gas emissions from boreal fires.  相似文献   

On resonant Rossby–Haurwitz triads     

By PETER LYNCH 《地球，A辑:动力气象学与海洋学》2009,61(3):438-445

The dynamics of non-divergent flow on a rotating sphere are described by the conservation of absolute vorticity. The analytical study of the non-linear barotropic vorticity equation is greatly facilitated by the expansion of the solution in spherical harmonics and truncation at low order. The normal modes are the well-known Rossby–Haurwitz (RH) waves, which represent the natural oscillations of the system. Triads of RH waves, which satisfy conditions for resonance, are of critical importance for the distribution of energy in the atmosphere.
We show how non-linear interactions of resonant RH triads may result in dynamic instability of large-scale components. We also demonstrate a mathematical equivalence between the equations for an orographically forced triad and a simple mechanical system, the forced-damped swinging spring. This equivalence yields insight concerning the bounded response to a constant forcing in the absence of damping. An examination of triad interactions in atmospheric reanalysis data would be of great interest.  相似文献   

On the observability of chemical and physical aerosol properties by optical observations: Inverse modelling with variational data assimilation     

By MICHAEL KAHNERT 《Tellus. Series B, Chemical and physical meteorology》2009,61(5):747-755

Determining size-resolved chemical composition of aerosols is important for modelling the aerosols' direct and indirect climate impact, for source–receptor modelling, and for understanding adverse health effects of particulate pollutants. Obtaining this kind of information from optical remote sensing observations is an ill-posed inverse problem. It can be solved by variational data assimilation in conjunction with an aerosol transport model. One important question is how much information about the particles' physical and chemical properties is contained in the observations. We perform a numerical experiment to test the observability of size-dependent aerosol composition by remote sensing observations. An aerosol transport model is employed to produce a reference and a perturbed aerosol field. The perturbed field is taken as a proxy for a background estimate subject to uncertainties. The reference result represents the 'true' state of the system. Optical properties are computed from the reference results and are assimilated into the perturbed model. The assimilation results reveal that inverse modelling of optical observations significantly improves the background estimate. However, the optical observations alone do not contain sufficient information for producing a faithful retrieval of the size-resolved aerosol composition. The total mass mixing ratios, on the other hand, are retrieved with remarkable accuracy.  相似文献   

Vertical profiling of convective dust plumes in southern Morocco during SAMUM     

By ALBERT ANSMANN  MATTHIAS TESCHE  PETER KNIPPERTZ  EIKE BIERWIRTH  DIETRICH ALTHAUSEN  DETLEF MÜLLER  OLIVER SCHULZ 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):340-353

Lifting of dust particles by dust devils and convective plumes may significantly contribute to the global mineral dust budget. During the Saharan Mineral Dust Experiment (SAMUM) in May–June 2006 vertical profiling of dusty plumes was performed for the first time. Polarization lidar observations taken at Ouarzazate (30.9°N, 6.9°W, 1133 m height above sea level) are analyzed. Two cases with typical and vigorous formation of convective plumes and statistical results of 5 d are discussed. The majority of observed convective plumes have diameters on order of 100–400 m. Most of the plumes (typically 50–95%) show top heights <1 km or 0.3DLH with the Saharan dust layer height DLH of typically 3–4 km. Height-to-diameter ratio is mostly 2–10. Maximum plume top height ranges from 1.1 to 2.9 km on the 5 d. 5–26 isolated plumes and clusters of plumes per hour were detected. A low dust optical depth (<0.3) favours plume evolution. Observed surface, 1 and 2–m air temperatures indicate that a difference of 17–20 K between surface and 2-m air temperature and of 0.9–1 K between the 1 and 2-m temperatures are required before convective plumes develop. Favourable horizontal wind speeds are 2–7 m s⁻¹.  相似文献   

Spectral absorption coefficients and imaginary parts of refractive indices of Saharan dust during SAMUM-1     

By T. MÜLLER  A. SCHLADITZ  A. MASSLING  N. KAADEN  K. KANDLER  A. WIEDENSOHLER 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):79-95

During the SAMUM-1 experiment, absorption coefficients and imaginary parts of refractive indices of mineral dust particles were investigated in southern Morocco. Main absorbing constituents of airborne samples were identified to be iron oxide and soot. Spectral absorption coefficients were measured using a spectral optical absorption photometer (SOAP) in the wavelength range from 300 to 800 nm with a resolution of 50 nm. A new method that accounts for a loading-dependent correction of fibre filter based absorption photometers, was developed. The imaginary part of the refractive index was determined using Mie calculations from 350 to 800 nm. The spectral absorption coefficient allowed a separation between dust and soot absorption. A correlation analysis showed that the dust absorption coefficient is correlated ( R ² up to 0.55) with the particle number concentration for particle diameters larger than 0.5 μm, whereas the coefficient of determination R ² for smaller particles is below 0.1. Refractive indices were derived for both the total aerosol and a dust aerosol that was corrected for soot absorption. Average imaginary parts of refractive indices of the entire aerosol are 7.4 × 10⁻³, 3.4 × 10⁻³ and 2.0 × 10⁻³ at wavelengths of 450, 550 and 650 nm. After a correction for the soot absorption, imaginary parts of refractive indices are 5.1 × 10⁻³, 1.6 × 10⁻³ and 4.5 × 10⁻⁴.  相似文献   

How soon will climate records of the 20th century be broken according to climate model simulations?     

By Leena Ruokolainen  Jouni Räisänen 《地球，A辑:动力气象学与海洋学》2009,61(4):476-490

What will happen to local record values of temperature and precipitation in a world with ongoing global warming? Here we first examine how many of the observed local temperature maxima of 1901–2006 occurred in the years 2001–2006 and compare the observations with model simulations. Then we study whether, and how soon, the models simulate the climate records of the 20th century to be broken in the ongoing 21st century.
In 27% of our analysis area, the highest annual mean temperatures of the whole period 1901–2006 were observed in 2001–2006. For the 22 climate models in our study, this fraction varies from 17% to 70%, with a multimodel mean of 40%. In simulations based on the SRES A1B emissions scenario, the highest annual mean temperature of the 20th century is exceeded on average in 99% of the global area by the year 2080. The same number for the highest (lowest) annual precipitation total is 60% (43%). Monthly and seasonal temperature and precipitation records are also analysed, and the geographical distributions of record value occurrence are related to the distributions of time mean climate change and magnitude of interannual variability.  相似文献   

Effect of emission changes in Southeast Asia on global hydroxyl and methane lifetime     

By S. B. DALSØREN  I. S. A. ISAKSEN  L. LI  A. RICHTER 《Tellus. Series B, Chemical and physical meteorology》2009,61(4):588-601

We performed model studies on how anthropogenic emission changes in Southeast Asia (region between 60–150°E and 10°S–50°N) in the period 1980–2020 could contribute to changes in hydroxyl and methane lifetime on a global scale. From 1980 to 2000, we calculate small global OH and methane lifetime changes due to compensating effects by emission changes in Southeast Asia and emission changes in the rest of the world. There is no guarantee that this offset will persist in the future. Southeast Asia is going through rapid economic development and emission increases there may be a major driver for changes. The development of Asian emissions after year 2000 is under much debate and for this period we apply several emission scenarios. For most emission scenarios the simulated Southeast Asian induced changes in global hydroxyl and methane lifetime after year 2000 are moderate. However, an upper estimate assuming very high increases in NO _x emissions results in substantial increases of hydroxyl and corresponding reductions in global methane lifetime. Interestingly, for the high NO _x emission case our results fit very well with recent satellite observations on trends of NO₂ over central eastern China.  相似文献   

Variations of atmospheric nitrous oxide concentration in the northern and western Pacific     

By K. ISHIJIMA  T. NAKAZAWA  S. AOKI 《Tellus. Series B, Chemical and physical meteorology》2009,61(2):408-415

Atmospheric N₂O concentration was observed in the Pacific for the period 1991–2006, using commercial container ships sailing between Japan and North America and between Japan and Australia or New Zealand. The N₂O concentration showed a secular increase and interannual variations at all sampling locations, but a seasonal cycle was detectable only at northern high latitudes. The annual mean N₂O concentration showed little longitudinal variations (within ± 0.3 ppb) in the northern Pacific, but showed a clear north-south gradient of about 0.8 ppb, with higher values in the Northern Hemisphere. The annual mean N₂O was also characterized by especially high values at 30°N due to strong local N₂O emissions and by a steep latitudinal decrease from the equator to 20°S due to the suppression of interhemispheric exchange of air by the South Pacific Convergence Zone. The N₂O growth rate showed an interannual variation with a period of about 3 yr (high-values in 1999 and 2000), with a delayed eastward and poleward phase propagation in the northern and western Pacific, respectively. The interannual variations of the N₂O growth rate and soil water showed a good correlation, suggesting that the N₂O emission from soils have an important causative role in the atmospheric N₂O variation.  相似文献