oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
A new method to derive middle atmospheric temperature profiles using a combination of Rayleigh lidar and O2 airglow temperatures measurements
A. Taori, A. Jayaraman, K. Raghunath,V. Kamalakar
Annales Geophysicae (ANGEO) , 2012,
Abstract: The vertical temperature profiles in a typical Rayleigh lidar system depends on the backscatter photon counts and the CIRA-86 model inputs. For the first time, we show that, by making simultaneous measurements of Rayleigh lidar and upper mesospheric O2 temperatures, the lidar capability can be enhanced to obtain mesospheric temperature profile up to about 95 km altitudes. The obtained results are compared with instantaneous space-borne SABER measurements for a validation.
Lidar measurements of mesospheric temperature inversion at a low latitude  [PDF]
V. Siva Kumar,Y. Bhavani Kumar,K. Raghunath,P. B. Rao
Annales Geophysicae (ANGEO) , 2003,
Abstract: The Rayleigh lidar data collected on 119 nights from March 1998 to February 2000 were used to study the statistical characteristics of the low latitude mesospheric temperature inversion observed over Gadanki (13.5° N, 79.2° E), India. The occurrence frequency of the inversion showed semiannual variation with maxima in the equinoxes and minima in the summer and winter, which was quite different from that reported for the mid-latitudes. The peak of the inversion layer was found to be confined to the height range of 73 to 79 km with the maximum occurrence centered around 76 km, with a weak seasonal dependence that fits well to an annual cycle with a maximum in June and a minimum in December. The magnitude of the temperature deviation associated with the inversion was found to be as high as 32 K, with the most probable value occurring at about 20 K. Its seasonal dependence seems to follow an annual cycle with a maximum in April and a minimum in October. The observed characteristics of the inversion layer are compared with that of the mid-latitudes and discussed in light of the current understanding of the source mechanisms. Key words. Atmospheric composition and structure (pressure, density and temperature). Meterology and atmospheric dynamics (climatology)
Upper altitude limit for Rayleigh lidar
P. S. Argall
Annales Geophysicae (ANGEO) , 2007,
Abstract: It has long been assumed that Rayleigh lidar can be used to measure atmospheric temperature profiles up to about 90 or 100 km and that above this region the technique becomes invalid due to changes in atmospheric composition which affect basic assumptions on which Rayleigh lidar is based. Modern powerful Rayleigh lidars are able to measure backscatter from well above 100 km requiring a closer examination of the effects of the changing atmospheric composition on derived Rayleigh lidar temperature profiles. The NRLMSISE-00 model has been used to simulate lidar signal (photon-count) profiles, taking into account the effects of changing atmospheric composition, enabling a quantitative analysis of the biases and errors associated with extending Rayleigh lidar temperature measurements above 100 km. The biases associated with applying a nominal correction for the change in atmospheric composition with altitude has also been investigated. The simulations reported here show that in practice the upper altitude limit for Rayleigh lidar is imposed more by the accuracy of the temperature or pressure used to seed the temperature retrieval algorithm than by accurate knowledge of the atmospheric composition as has long been assumed.
Polar middle atmosphere temperature climatology from Rayleigh lidar measurements at ALOMAR (69° N)
A. Sch ch, G. Baumgarten,J. Fiedler
Annales Geophysicae (ANGEO) , 2008,
Abstract: Rayleigh lidar temperature profiles have been derived in the polar middle atmosphere from 834 measurements with the ALOMAR Rayleigh/Mie/Raman lidar (69.3° N, 16.0° E) in the years 1997–2005. Since our instrument is able to operate under full daylight conditions, the unique data set presented here extends over the entire year and covers the altitude region 30 km–85 km in winter and 30 km–65 km in summer. Comparisons of our lidar data set to reference atmospheres and ECMWF analyses show agreement within a few Kelvin in summer but in winter higher temperatures below 55 km and lower temperatures above by as much as 25 K, due likely to superior resolution of stratospheric warming and associated mesospheric cooling events. We also present a temperature climatology for the entire lower and middle atmosphere at 69° N obtained from a combination of lidar measurements, falling sphere measurements and ECMWF analyses. Day to day temperature variability in the lidar data is found to be largest in winter and smallest in summer.
Study of the tidal variations in mesospheric temperature at low and mid latitudes from WINDII and potassium lidar observations
M. Shepherd,C. Fricke-Begemann
Annales Geophysicae (ANGEO) , 2004,
Abstract: Zonal mean daytime temperatures from the Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS) and nightly temperatures from a potassium (K) lidar are employed in the study of the tidal variations in mesospheric temperature at low and mid latitudes in the Northern Hemisphere. The analysis is applied to observations at 89km height for winter solstice, December to February (DJF), at 55° N, and for May and November at 28° N. The WINDII results are based on observations from 1991 to 1997. The K-lidar observations for DJF at Kühlungsborn (54° N) were from 1996–1999, while those for May and November at Tenerife 28° N were from 1999. To avoid possible effects from year-to-year variability in the temperatures observed, as well as differences due to instrument calibration and observation periods, the mean temperature field is removed from the respective data sets, assuming that only tidal and planetary scale perturbations remain in the temperature residuals. The latter are then binned in 0.5h periods and the individual data sets are fitted in a least-mean square sense to 12-h and 8-h harmonics, to infer semidiurnal and terdiurnal tidal parameters. Both the K-lidar and WINDII independently observed a strong semidiurnal tide in November, with amplitudes of 13K and 7.4K, respectively. Good agreement was also found in the tidal parameters derived from the two data sets for DJF and May. It was recognized that insufficient local time coverage of the two separate data sets could lead to an overestimation of the semidiurnal tidal amplitude. A combined ground-based/satellite data set with full diurnal local time coverage was created which was fitted to 24h+12h+8h harmonics and a novel method applied to account for possible differences between the daytime and nighttime means. The results still yielded a strong semidiurnal tide in November at 28° N with an amplitude of 8.8K which is twice the SD amplitude in May and DJF. The diurnal tidal parameters were practically the same at 28° N and 55° N, in November and DJF, respectively, with an amplitude of 6.5K and peaking at ~9h. The diurnal and semidiurnal amplitudes in May were about the same, 4K, and 4.6K, while the terdiurnal tide had the same amplitudes and phases in May and November at 28° N. Good agreement is found with other experimental data while models tend to underestimate the amplitudes. Key words. Atmospheric composition and structure (pressure, density and temperature) – Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)
A comparison of Rayleigh and sodium lidar temperature climatologies
P. S. Argall ,R. J. Sica
Annales Geophysicae (ANGEO) , 2007,
Abstract: Temperature measurements from the PCL Rayleigh lidar located near London, Canada, taken during the 11 year period from 1994 to 2004 are used to form a temperature climatology of the middle atmosphere. A unique feature of the PCL temperature climatology is that it extends from 35 to 95 km allowing comparison with other Rayleigh lidar climatologies (which typically extend up to about 85 km), as well as with climatologies derived from sodium lidar measurements which extend from 83 to 108 km. The derived temperature climatology is compared to the CIRA-86 climatological model and to other lidar climatologies, both Rayleigh and sodium. The PCL climatology agrees well with the climatologies of other Rayleigh lidars from similar latitudes, and like these other climatologies shows significant differences from the CIRA-86 temperatures in the mesosphere and lower thermosphere. Significant disagreement is also found between the PCL climatology and sodium lidar climatologies measured in the central and western United States at similar latitudes, with the PCL climatology consistently 10 to 15 K cooler in the 85 to 90 km region.
Mesospheric turbulent velocity estimation using the Buckland Park MF radar  [PDF]
D. A. Holdsworth,R. A. Vincent,I. M. Reid
Annales Geophysicae (ANGEO) , 2003,
Abstract: This paper investigates turbulent velocity estimation using the full correlation analysis (FCA) of spaced antenna (SA) data, and its application to the routine FCA observations of the Buckland Park MF (BPMF) radar. The effects of transmitter beamwidths are investigated, confirming the suggestions of previous authors that wide transmit beam widths lead to an overestimation of the turbulent velocity. The annual variation of the turbulent velocity is investigated, revealing an increase in turbulent velocity with height, and equinoctal minima and solstice maxima observed below 80 km. Investigations of the turbulent velocities about the March diurnal tide maximum reveals a diurnal variation in phase with the zonal velocity. Harmonic analysis reveals this relationship exists between February and September. Descending power layers are also observed during this period. A number of mechanisms are proposed to describe these observations. Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; instruments and techniques) – Radio science (instruments and techniques)
MF radar observations of mean winds and tides over Poker Flat, Alaska (65.1° N, 147.5° W)  [PDF]
P. Kishore,S. P. Namboothiri,K. Igarashi,Y. Murayama
Annales Geophysicae (ANGEO) , 2003,
Abstract: MF radar wind measurements in the mesosphere and lower thermosphere over Poker Flat, Alaska (65.1° N, 147.5° W) are used to study the features of mean winds and solar tides. Continuous observation with the newly installed radar is in progress and in the present study we have analyzed a database of the first 27 months (October 1998–December 2000) of observation. The observed mean wind climatology has been compared with previous measurements and the latest empirical model values (HWM93 model). Similarly, the tidal characteristics are described and compared with the Global Scale Wave Model (GSWM00). The mean wind characteristics observed are fairly consistent with previous wind measurements by the Poker Flat MST radar. The main feature of the zonal circulation is the annual variation with summer westward flow and winter eastward flow. The annual mean zonal wind has a west-ward motion at altitudes below 90 km. The annual mean meridional circulation has mainly southward motion at 70–100 km. There is very good agreement between the radar zonal winds and the HWM93 model winds. Comparison of the meridional winds shows some discrepancy. Analysis of two years of data indicated that the year-to-year consistency is preserved in the mean circulation in the mesosphere. Tidal characteristics observed are also consistent with previous measurements. Semidiurnal tides have the largest amplitudes in summer while the weakest amplitude is observed during the winter months. The vertical wavelength is longer during the summer season compared to the winter season. Comparison with the GSWM00 produces mixed results. There is reasonable agreement between the observed and modeled phases. Diurnal tide amplitudes are comparable in magnitude with that of the semidiurnal tide. Seasonal variation is less evident in the amplitudes. Comparison of the observed tidal parameters with the GSWM00 reveals some agreement and discrepancies. Key words. Meteorology and atmospheric dynamics (climatology; middle atmosphere dynamics; waves and tides)
Studies on geoeffectiveness of coronal mass ejections and near-earth space environment
日冕物质抛射的对地有效性和近地空间环境的研究

XUE Xiang-Hui,DOU Xian-Kang,
薛向辉
,窦贤康

中国科学院研究生院学报 , 2010,
Abstract: This work focused on the two aspects of the space weather.One is the sources of the disaster space weather-coronal mass ejections(CME). We set up a new ice-cream cone model to describle the CMEs and discussed the geoeffectiveness of CMEs.The other is the end of the space weather-near-Earth environment. We introduced a newly installed Mie-Rayleigh-Sodium fluorescent lidar and its initial observations for the sodium layer between 80~110km,and also employed a meteor radar to study the mesospheric and low-thermospheric tides by canonical correlation alaysis.
The ALOMAR Rayleigh/Mie/Raman lidar: objectives, configuration, and performance  [PDF]
U. von Zahn,G. von Cossart,J. Fiedler,K. H. Fricke
Annales Geophysicae (ANGEO) , 2003,
Abstract: We report on the development and current capabilities of the ALOMAR Rayleigh/Mie/Raman lidar. This instrument is one of the core instruments of the international ALOMAR facility, located near Andenes in Norway at 69°N and 16°E. The major task of the instrument is to perform advanced studies of the Arctic middle atmosphere over altitudes between about 15 to 90 km on a climatological basis. These studies address questions about the thermal structure of the Arctic middle atmosphere, the dynamical processes acting therein, and of aerosols in the form of stratospheric background aerosol, polar stratospheric clouds, noctilucent clouds, and injected aerosols of volcanic or anthropogenic origin. Furthermore, the lidar is meant to work together with other remote sensing instruments, both ground- and satellite-based, and with balloon- and rocket-borne instruments performing in situ observations. The instrument is basically a twin lidar, using two independent power lasers and two tiltable receiving telescopes. The power lasers are Nd:YAG lasers emitting at wavelengths 1064, 532, and 355 nm and producing 30 pulses per second each. The power lasers are highly stabilized in both their wavelengths and the directions of their laser beams. The laser beams are emitted into the atmosphere fully coaxial with the line-of-sight of the receiving telescopes. The latter use primary mirrors of 1.8 m diameter and are tiltable within 30° off zenith. Their fields-of-view have 180 μrad angular diameter. Spectral separation, filtering, and detection of the received photons are made on an optical bench which carries, among a multitude of other optical components, three double Fabry-Perot interferometers (two for 532 and one for 355 nm) and one single Fabry-Perot interferometer (for 1064 nm). A number of separate detector channels also allow registration of photons which are produced by rotational-vibrational and rotational Raman scatter on N2 and N2+O2 molecules, respectively. Currently, up to 36 detector channels simultaneously record the photons collected by the telescopes. The internal and external instrument operations are automated so that this very complex instrument can be operated by a single engineer. Currently the lidar is heavily used for measurements of temperature profiles, of cloud particle properties such as their altitude, particle densities and size distributions, and of stratospheric winds. Due to its very effective spectral and spatial filtering, the lidar has unique capabilities to work in full sunlight. Under these conditions it can measure temperatures up to 65 k
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.