2,261 research outputs found
Cooling of the Martian thermosphere by CO2 radiation and gravity waves: An intercomparison study with two general circulation models
No full textObservations show that the lower thermosphere of Mars (approximate to 100-140km) is up to 40K colder than the current general circulation models (GCMs) can reproduce. Possible candidates for physical processes missing in the models are larger abundances of atomic oxygen facilitating stronger CO2 radiative cooling and thermal effects of gravity waves. Using two state-of-the-art Martian GCMs, the Laboratoire de Meteorologie Dynamique and Max Planck Institute models that self-consistently cover the atmosphere from the surface to the thermosphere, these physical mechanisms are investigated. Simulations demonstrate that the CO2 radiative cooling with a sufficiently large atomic oxygen abundance and the gravity wave-induced cooling can alone result in up to 40K colder temperature in the lower thermosphere. Accounting for both mechanisms produce stronger cooling at high latitudes. However, radiative cooling effects peak above the mesopause, while gravity wave cooling rates continuously increase with height. Although both mechanisms act simultaneously, these peculiarities could help to further quantify their relative contributions from future observations
Upper tropospheric cloud systems determined from IR Sounders and their influence on the atmosphere
No full textInfrared Radiation in the Mesosphere and Lower Thermosphere: Energetic Effects and Remote Sensing
No full textInternational audienceThis paper discusses the formation mechanisms of infrared radiation in the mesosphere and lower thermosphere (MLT), the energetic effects of the radiative absorption/emission processes, and the retrieval of atmospheric parameters from infrared radiation measurements. In the MLT and above, the vibrational levels of the molecules involved in radiative transitions are not in local thermodynamic equilibrium (LTE) with the surrounding medium, and this then requires specific theoretical treatment. The non-LTE models for CO2, O3, and H2O molecules are presented, and the radiative cooling/heating rates estimated for five typical atmospheric scenarios, from polar winter to polar summer, are shown. An optimization strategy for calculating the cooling/heating rates in general circulation models is proposed, and its accuracy is estimated for CO2. The sensitivity of the atmospheric quantities retrieved from infrared observations made from satellites to the non-LTE model parameters is shown. © 2012 Springer Science+Business Media Dordrecht
Diurnal variation of high-level clouds from the synergy of AIRS and IASI space-borne infrared sounders
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Angular Correlations with Charmed Hadrons in the Monte-Carlo Model with String Repulsion
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Theoretical Investigation of Amplified Spontaneous Emission with Picosecond Light Pulses in Dye Solutions
No full textРождение странных частиц в рамках модели мультипомеронного обмена
No full textAn extended version of the multi-pomeron exchange model for the description of pp-collisions in a wide energy range (from ISR to LHC) is presented by accounting of strange particle yields. This model effectively includes the interaction of the quark-gluon strings in the form of fusion. Differentiation of yields of various particle types is carried out in accordance with the Schwinger mechanism of string hadronization. The results on the multiplicity of strange particles, their transverse momentum and correlations are presented. A comparison with experimental data is performed. The possible influence of higher resonances on the observables, as well as the applicability of the Schwinger mechanism is discussed.Авторы выражают благодарность гранту Санкт-Петербургского государственного университета 11.38.242.2015. Работа В. Н. Коваленко была выполнена при поддержке специальной ректорской стипендии СПбГУ, гранта фонда «Династия» и стипендии G-RISC.Предлагается расширенный вариант модели мультипомеронного обмена для описания процессов в pp-столкновениях в широком диапазоне энергий (от ISR к LHC) с учетом рождения странных частиц. В данной модели используется эффективное взаимодействие кварк-глюонных струн через их слияние. Дифференциация выходов разных типов частиц происходит в соответствии с механизмом Швингера для адронизации струны. Представлены результаты по множественности странных частиц, их поперечному импульсу и корреляциям. Проведено сравнение с экспериментальными данными. Обсуждается возможное влияние высших резонансов на наблюдаемые характеристики, а также применимость механизма Швингера
Photodissociation Dynamics of the Iodine-Arene Charge-Transfer Complex
No full textThe photodissociation reaction of the molecular iodine:arene charge-transfer (CT) complex into an iodine atom and an iodine atom-arene fragment has been investigated using femtosecond pump-probe, resonance Raman, and molecular dynamics simulations. In the condensed phase the reaction proceeds on a time scale of less than 25 fs, in sharp contrast to the gas phase where the excited state lifetime of the complex is about 1 ps. Since little CT resonance enhancement is found in Raman studies on the I2-stretch vibration, it is concluded that rapid curve crossing occurs from the CT state to a dissociative surface. Of particular interest is the finding that the polarization anisotropy of the iodine atom:arene (I:ar) photoproduct decays on a time scale of 350 fs both in pure arene solvents as well as in mixed arene/cyclohexane solutions. This latter finding rules out that secondary I:ar complex formation is the main cause of this ultrafast depolarization effect. The initial polarization anisotropy is found to be ~0.12 in pure mesitylene and ~0.34 in mixed mesitylene/cyclohexane solutions. Semiempirical configuration-interaction calculations show that, except for the axial CT complex, the transition dipole is aligned almost parallel to the normal of the arene plane. The oscillator strength of the CT transition is found to be maximal in the oblique conformation with the I2 molecule positioned at an angle of about 30° with respect to the arene normal. This iodine angular dependence of the oscillator strength leads to photoselection of bent I2:ar complexes in pump-probe experiments. Molecular dynamics simulations confirm earlier findings that the I2:benzene complex is a fragile entity and that it persists only for a few hundred femtoseconds. These simulations also provide the proper time scale for the decay of the polarization anisotropy. The fact that the photoproduct experiences a substantial torque in the dissociation process explains the absence of a cage effect in this reaction.
Evidence of a significant rotational non-LTE effect in the CO<sub>2</sub> 4.3 µm PFS-MEX limb spectra
No full textSince January 2004, the planetary Fourier spectrometer (PFS) on
board the Mars Express satellite has been recording near-infrared limb
spectra of high quality up to the tangent altitudes ≈ 150 km, with
potential information on density and thermal structure of the upper Martian
atmosphere. We present first results of our modeling of the PFS short
wavelength channel (SWC) daytime limb spectra for the altitude region above
90 km. We applied a ro-vibrational non-LTE model based on the stellar
astrophysics technique of accelerated lambda iteration (ALI) to solve the
multi-species and multi-level CO2 problem in the Martian atmosphere. We
show that the long-standing discrepancy between observed and calculated
spectra in the cores and wings of 4.3 µm region is explained by the
non-thermal rotational distribution of molecules in the upper vibrational
states 10011 and 10012 of the CO2 main isotope second hot (SH) bands
above 90 km altitude. The redistribution of SH band intensities from band
branch cores into their wings is caused (a) by intensive production of the
CO2 molecules in rotational states with j > 30 due to the absorption of
solar radiation in optically thin wings of 2.7 µm bands and (b) by a
short radiative lifetime of excited molecules, which is insufficient at
altitudes above 90 km for collisions to maintain rotation of excited
molecules thermalized. Implications for developing operational algorithms for
massive processing of PFS and other instrument limb observations are
discussed
Ice water content vertical profiles of high-level clouds: classification and impact on radiative fluxes
No full textInternational audienceIn this work, we discuss the shape of ice water content (IWC) vertical profiles in high ice clouds and its effect on radiative properties of these clouds, both in short- and in long-wave bands (SW and LW). Based on the analysis of colocated satellite data, we suggest a minimal set of primitive shapes (rectangular, isosceles trapezoid, lower and upper triangle), which sufficiently well represents the IWC profiles. About 75% of all high-level ice clouds (P 300 W m−2
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