Results 1 - 10 of 1429
Results 1 - 10 of 1429. Search took: 0.023 seconds
|Sort by: date | relevance|
[en] Despite the small interannual variation in the stratosphere in the northern summer, there is a distinct signal of the 11-year solar cycle in the geopotential heights and temperatures. Unlike the stratosphere in winter, when it is necessary to group the data according to the phase of the quasi-biennial oscillation (QBO) to obtain a statistically significant response to the solar cycle, the summer stratosphere has the same pattern for the full time series as for east and west years in the QBO. In all three series the pattern is statistically significant in summer
[en] Complete text of publication follows. There may exist questions concerning the agreement between temperature retrieved from satellites monitoring the upper stratosphere and mesosphere. The indication is that they do provide reasonably similar temperature profiles, i.e., differences exist but may be insignificant. It is unavoidable that the satellite soundings are not coincidental in time or in location and as a result comparison of these profiles are inexact. We will compare early comparisons of conjunctive inflatable falling sphere and satellite measurements, e.g., HALOE, AIRS, SABER, and possibly others as a surrogate method to infer accuracy between temperature retrievals. Comparison of measurements mainly in polar latitudes will establish the retrieval comparability. Our emphasis is to illustrate how well the retrievals representative the polar summer mesosphere. Whether large differences between remotely sensed temperatures are within expected accuracy bounds will be discussed using profiles between 60-90 km.
[en] Complete text of publication follows. To investigate the effects of decadal solar variability in temperature and ozone, along with interconnections to other features of the middle atmosphere, the data obtained from the Halogen Occultation Experiment (HALOE) aboard Upper Atmospheric Research Satellite (UARS) during the period 1992-2005 have been analyzed using a multifunctional regression model. The inferred annual-mean solar effect on temperature is found to be positive in the lower stratosphere and near stratopause, while it is negative in the middle stratosphere. In the mesosphere it is of the order of 0.5-1K/100sfu. The inferred solar effect on ozone is found to be significant in most of the stratosphere (2±1.1 - 4±1.6 % / 100 sfu), it is insignificant in the lower mesosphere whereas it is of the order of 5%/100sfu in the upper mesosphere. The results over stratosphere are compared with solar response obtained from SAGE II data for the same period. In general, responses of solar signal in temperature and ozone profiles show good agreement for HALOE and SAGE II measurements. Both the data sets show that, the solar effects on ozone and temperature are found to vary dramatically during some months, at least in some altitude regions. Solar effects on temperature are found to be negative during autumn while solar effects on ozone show maximum the next season (winter). Details will be discussed.
[en] Complete text of publication follows. The presentation is focused on the global spatial (altitude and latitude) structure, seasonal and interannual variability of the ∼5-day Rossby (W1) and ∼6-day Kelvin (E1) waves derived from the SABER/TIMED temperature measurements for full 6 years (January 2002-December 2007). The latitude structure of the ∼5-day W1 wave is related to the gravest symmetric wave number 1 Rossby wave, i.e. the (1,1) mode. Its seasonal behavior is dominated by equinoctial amplifications; in the NH the wave amplifies in March-April and September, while in the SH - in March and November. The vertical structure of the ∼5-day Rossby wave amplitude revealed double-peaked maxima centered at ∼80-90 km in the mesosphere and ∼105-110 km in the lower thermosphere, as the lower thermospheric maximum is at least two times stronger than the mesospheric one. This is a vertically propagating wave from the stratosphere up to 120 km altitude with a mean vertical wavelength of ∼50-60 km. The ∼5-day Rossby wave at middle latitudes (40 deg) revealed some interannual variability and at least part of it is connected with the effect of QBO. The ∼6-day E1 wave is equatorially trapped wave located between 20 deg N and 20 deg S. Its seasonal behavior indicated some equinoctial and June solstice amplifications. The altitude structure of the ∼6-day Kelvin wave phase indicated that this is a vertically propagating wave up to 110 km altitude. The mean vertical wavelength in the stratosphere and mesosphere is ∼25 km, however above 95 km altitude the vertical wavelength shortened to 15 km. The ∼6-day Kelvin wave indicated significant SAO and QBO variability.
[en] The menace of supersonic aircraft and bomb aerosol against the ozone layer that shields earth from most of the sun cancer-providing ultraviolet rays is examined. Large research programs are developed in view of answering the question, but the models proposed still yield controversial data
[fr]On examine quelle menace l'aviation supersonique et les bombes aerosols font peser sur la couche d'ozone qui protege la terre des rayons ultraviolets du soleil. Va-t-on voir le nombre des cancers de la peau augmenter de maniere significative. De vastes programmes de recherche tentent de repondre a ces questions, mais les modeles proposes et les chiffres obtenus sont encore tres controverses
[en] Complete text of publication follows. Gravity (buoyancy) waves play an important role in transferring momentum from source regions in the lower atmosphere to the middle and upper atmosphere. Body forces produced by breaking waves lead to residual circulations that profoundly affect the state of the atmosphere. This talk will summarize results from a campaign held near Darwin in northern Australia in January-February 2006 to measure wave generation and propagation and the associated momentum fluxes. The project used a variety of radars to study the spatial and temporal variability of rainfall and the associated latent heat release during large convective storms. A high-resolution numerical model utilized the latent heat release to compute the spatial and geographic variation of gravity wave generation and propagation into the lower stratosphere. Gravity wave ray-tracing techniques were then used to estimate the wave flux penetrating to heights near 90 km, where the results were compared with direct measurements made using a meteor radar. It is shown that there is excellent agreement between the direct and indirect estimates of wave activity. Wave fluxes show a high degree of temporal variability, with consequent variability in momentum flux deposition and wave drag.
[en] In earlier work it was concluded that the large (0.3μ rad) particles of the stratospheric aerosol layer are formed by a heterogeneous nucleation process, and that a primary factor controlling the particle size distribution of the aerosol is the number of particles available to serve as nucleation sites for the subsequent heterogeneous formation process. In this paper two possible sources of these sites are considered; transport from the troposphere, and homogeneous formation in the stratosphere. Using a simple numerical model, it is shown that if homogeneous nucleation occurred in the stratosphere it would, in general, result in the formation of relatively large (10cm-3) numbers of new particles, which previous work has shown to be incompatible with the formation of the observed large particles. It is also pointed out that vertical diffusive transport from the troposphere would also introduce unacceptably large numbers of particles, but that vertical advection, in which air enters the stratosphere in the updrafts of intense tropical thunderstorms, would have the requisite low particle concentrations and also be compatible with other observed properties of the stratospheric aerosol layer
[fr]Dans un travail precedent, on est arrive a la conclusion que les grandes particules (0,3 μm de rayon) de la couche stratospherique d'aerosols sont formes par un processus de nucleation heterogene et qu'un facteur important de la distribution en taille des aerosols est le nombre de particules susceptibles de servir de noyau dans ce processus heterogene. Dans cet article, on envisage deux sources possibles pour ces noyaux: leur transport depuis la troposphere et leur formation homogene dans la stratosphere. En utilisant un modele numerique simple, on montre que si une nucleation homogene avait lieu dans la stratosphere, il en resulterait en general un nombre relativement grand (10 cm-3) de nouvelles particules, ce qui, compte tenu de nos travaux precedents, apparait incompatible avec la formation des grandes particules telles qu'elles sont observees. On remarque egalement qu'un transport vertical par diffusion, depuis la troposphere conduirait aussi a un nombre trop grand de particules. Au contraire, si l'air etait entraine dans la stratosphere par un mouvement ascensionnel au cours des orages tropicaux intenses, cette advection verticale conduirait a la faible concentration de particules attendue, et serait egalement compatible avec les autres proprietes de la couche stratospherique d'aerosols
[en] Complete text of publication follows. A numerical two-dimensional interactive dynamical-radiative-photochemical model including aerosol physics is used to examine the expected long-term changes in stratospheric temperature and the Earth's ozone layer due to anthropogenic pollution of the atmosphere by the greenhouse gases CO2, CH4, N2O and by ozone-depleting chlorine and bromine compounds. The model time-dependent runs were made for the period from 1975 to 2050. The mechanisms of the impact of each of the pollutants on stratospheric temperature have been analysed, their relative contributions to the predicted temperature change have been estimated. The processes, which determine the influence of anthropogenic growth of atmospheric abundance of the greenhouse gases on the dynamics of recovery of the Earth's ozone layer after reduction of anthropogenic discharges of ozone-depleting chlorine and bromine compounds into the atmosphere, have been studied in details. The contributions of different pollutions to the predicted ozone changes have been estimated. The results of the calculations show that the basic mechanism by which greenhouse gases influence the ozone layer is stratospheric cooling accompanied by a weakness in the efficiency of the catalytic cycles of ozone destruction due to temperature dependencies of the photochemical gas-phase reactions. Modification of polar stratospheric clouds (PSCs) caused by anthropogenic growth of the greenhouse gases is important only for the polar ozone. An essential influence of the greenhouse gases on the ozone by a modification of the stratospheric sulphate aerosol is revealed. The aerosol changes caused by the greenhouse gases modify the distribution of the ozone-active gaseous chlorine, bromine and nitrogen components by means of heterogeneous reactions on the aerosol surface, resulting in a significant decrease in springtime polar ozone depletion of the Antarctic ozone hole.