Upper Atmospheric Winds Research Articles

Long Term Variations in the Length of Day and Climatic Change

Summary The long-period (greater than about 10 yr) variations in the length-of-day (LOD) observed since 1820 show a marked similarity with variations observed in various climatic indices; periods of acceleration of the Earth corresponding to years of increasing intensity of the zonal circulation and to global-surface warming: periods of deceleration corresponding to years of decreasing zonal-circulation intensity and to a global decrease in surface temperatures. The long-period atmospheric excitation functions for near-surface geostrophic winds, for changes in the atmospheric mass distribution and for eustatic variations in sea level have been evaluated and correlate well with the observed changes in the LOD; although their total effect represents only about 10 per cent of the required excitation. The computed excitation lags the LOD variations by about 10-15 yr. Upper atmospheric winds or other meteorological related factors appear to be quite inadequate to provide the additional driving force that is required if the LOD changes are of meteorological origin. Instead, it appears that the LOD fluctuations and the climatic variations on a time scale of 20-30 yr may have a common origin as has been suggested by Anderson. That is, the results suggest that indirect solid Earth effects on climate may be important.

TIMED Doppler Interferometer on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite: Data product overview

The TIMED Doppler Interferometer (TIDI) performs the measurement of upper atmospheric winds on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite. This is an optimized single etalon Fabry Perot interferometer that records the slight Doppler shift of individual emission features of the O2 (0,0) atmospheric band. The interferometer operates at a 100% duty cycle obtaining neutral wind altitude profiles on a global basis. The measurements are synoptic and provide an uninterrupted long‐term climatological record of the dynamics in the mesosphere and lower thermosphere regions. The data products from TIDI include (1) apparent line of sight winds and integrated brightness, (2) inverted line of sight winds and volume emission rate, and (3) inverted horizontal neutral wind fields on an evenly spaced track angle/altitude grid. The data products demonstrate an interannual variability in the tidal structure of the mesosphere and the lower thermosphere and an inherent daily geophysical variance.

TIMED Doppler Interferometer: Overview and recent results

The Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics (TIMED) satellite carries a limb‐scanning Fabry‐Perot interferometer designed to perform remote‐sensing measurements of upper atmosphere winds and temperatures globally. This instrument is called the TIMED Doppler Interferometer, or TIDI. This paper provides an overview of the TIDI instrument design, on‐orbit performance, operational modes, data processing and inversion procedures, and a summary of wind results to date. Daytime and nighttime neutral winds in the mesosphere and lower thermosphere/ionosphere (MLTI) are measured on TIDI using four individual scanning telescopes that collect light from various upper atmosphere airglow layers on both the cold and warm sides of the high‐inclination TIMED spacecraft. The light is spectrally analyzed using an ultrastable plane etalon Fabry‐Perot system with sufficient spectral resolution to determine the Doppler line characteristics of atomic and molecular emissions emanating from the MLTI. The light from all four telescopes and from an internal calibration field passes through the etalon and is combined on a single image plane detector using a Circle‐to‐Line Interferometer Optic (CLIO). The four geophysical fields provide orthogonal line‐of‐sight measurements to either side of the satellite's path and these are analyzed to produce altitude profiles of vector winds in the MLTI. The TIDI wind measurements presented here are from the molecular oxygen (0‐0) band, covering the altitude region 85–105 km. The unique TIDI design allows for more extended local time coverage of wind structures than previous wind‐measuring instruments from high‐inclination satellites. The TIDI operational performance has been nominal except for two anomalies: (1) higher than expected background white light caused by a low‐level light leak and (2) ice deposition on cold optical surfaces. Both anomalies are well understood and the instrumental modes and data analysis techniques have been adjusted to mitigate their effects on data quality. The analysis techniques used to derive winds are described. The TIDI wind measurements from multiple yaw cycles of TIMED have been used to extract migrating diurnal and semidiurnal tides. The migrating tide results are compared with predictions from the Global Scale Wave Model (GSWM), and results from the Upper Atmospheric Research Satellite, High Resolution Doppler Imager (HRDI) instrument. TIDI wind measurements are also compared with ground‐based meteor radar observations, showing consistent results.

Characteristics of infrasound signals from earthquakes

Analysis of infrasound signals is presented for a set of 31 earthquakes located mostly in the western United States and recorded at infrasound arrays operated by the Los Alamos National Laboratory. By normalizing measured amplitudes for the effects of propagation and distance, a pressure-amplitude versus earthquake magnitude relation is derived. Further analysis showed that the observed variance in this relation is likely due to the variation in source ground motion and variation in upper atmospheric winds. Signal durations can be tens of minutes and azimuth deviations have a mean of three degrees (measured from array data compared to great circle azimuths). Other characteristics of the infrasound data will be discussed. Our analysis of the observed data combined with surface ground motion accelerations, led to estimates of the minimum surface accelerations needed to generated infrasound signals measured at distant arrays.

Infrasound remote sensing of the upper atmosphere

We investigate the prospects for utilizing infrasound signals from geophysical sources to improve our knowledge of upper atmospheric winds and temperatures. We present results from numerical experiments designed to quantify the statistical performance of an idealized infrasonic upper atmospheric remote sensing network over a range of propagation modeling assumptions, source types, and geophysical variables. For a series of hypothetical events, infrasonic observables are calculated with a spherical 3-D ray tracer and series of atmospheric profiles spanning the range of geophysical parameters. These synthetic measurements are then inverted to estimate the original atmospheric background fields. A nonlinear least-squares estimation procedure that accounts for uncertainties in both the dependent and independent variables is used. The retrieved atmospheric profiles are represented by a set of truncated empirical orthogonal functions to incorporate a priori knowledge of atmospheric structure and reduce the number of parameters. Our numerical experiments indicate that it is indeed possible to make meaningful estimates of upper atmospheric environmental profiles with today’s infrasound networks. [Work supported by the Office Naval Research.]

Atmospheric densities derived from CHAMP/STAR accelerometer observations

The satellite CHAMP carries the accelerometer STAR in its payload and thanks to the GPS and SLR tracking systems accurate orbit positions can be computed. Total atmospheric density values can be retrieved from the STAR measurements, with an absolute uncertainty of 10–15%, under the condition that an accurate radiative force model, satellite macro-model, and STAR instrumental calibration parameters are applied, and that the upper-atmosphere winds are less than 150 m/ s . The STAR calibration parameters (i.e. a bias and a scale factor) of the tangential acceleration were accurately determined using an iterative method, which required the estimation of the gravity field coefficients in several iterations, the first result of which was the EIGEN-1S (Geophys. Res. Lett. 29 (14) (2002) 10.1029) gravity field solution. The procedure to derive atmospheric density values is as follows: (1) a reduced-dynamic CHAMP orbit is computed, the positions of which are used as pseudo-observations, for reference purposes; (2) a dynamic CHAMP orbit is fitted to the pseudo-observations using calibrated STAR measurements, which are saved in a data file containing all necessary information to derive density values; (3) the data file is used to compute density values at each orbit integration step, for which accurate terrestrial coordinates are available. This procedure was applied to 415 days of data over a total period of 21 months, yielding 1.2 million useful observations. The model predictions of DTM-2000 (EGS XXV General Assembly, Nice, France), DTM-94 (J. Geod. 72 (1998) 161) and MSIS-86 (J. Geophys. Res. 92 (1987) 4649) were evaluated by analysing the density ratios (i.e. “observed” to “computed” ratio) globally, and as functions of solar activity, geographical position and season. The global mean of the density ratios showed that the models underestimate density by 10–20%, with an rms of 16–20%. The binning as a function of local time revealed that the diurnal and semi-diurnal components are too strong in the DTM models, while all three models model the latitudinal gradient inaccurately. Using DTM-2000 as a priori, certain model coefficients were re-estimated using the STAR-derived densities, yielding the DTM-STAR test model. The mean and rms of the global density ratios of this preliminary model are 1.00 and 15%, respectively, while the tidal and latitudinal modelling errors become small. This test model is only representative of high solar activity conditions, while the seasonal effect is probably not estimated accurately due to correlation with the solar activity effect. At least one more year of data is required to separate the seasonal effect from the solar activity effect, and data taken under low solar activity conditions must also be assimilated to construct a model representative under all circumstances.

Atmospheric and oceanic excitation of length‐of‐day variations during 1980–2000

Although nontidal changes in the Earth's length‐of‐day on timescales of a few days to a few years are primarily caused by changes in the angular momentum of the zonal winds, other processes can be expected to cause the length‐of‐day to change as well. Here the relative contribution of upper atmospheric winds, surface pressure, oceanic currents, and ocean‐bottom pressure to changing the length‐of‐day during 1980–2000 is evaluated using estimates of atmospheric angular momentum from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis project, estimates of the angular momentum of the zonal winds in the upper atmosphere from the United Kingdom Meteorological Office, and estimates of oceanic angular momentum from the Estimating the Circulation and Climate of the Ocean consortium's simulation of the general circulation of the oceans. On intraseasonal timescales, atmospheric surface pressure, oceanic currents, and ocean‐bottom pressure are found to be about equally important in causing the length‐of‐day to change, while upper atmospheric winds are found to be less important than these mechanisms. On seasonal timescales, the upper atmospheric winds are more important than the sum of currents and bottom pressure in causing the length‐of‐day to change and, except at the annual frequency, are even more important than surface pressure changes. On interannual timescales, oceanic currents and ocean‐bottom pressure are found to be only marginally effective in causing the length‐of‐day to change.

Observation of rain area's motion using 12-Ghz satellite broadcasting wave

In this paper, the rain attenuation of satellite broadcasting signals at 12 GHz transmitted continuously for almost 24 hours is used for observation of the rain area. The rain attenuation of the satellite wave is measured at three locations on the ground and the rain intensity is measured at one of these locations. From the difference of start of attenuation we determine the direction of motion of the rain area, its moving speed, and its height and width. Further, the results are compared with values obtained from meteorological data such as upper-atmosphere winds and ground temperature. The results are very favorable. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(5): 21–30, 2001

Solar Forcing of Earth's Climate

The sun is the primary source of energy for the climate of the earth. Variations in solar energy reaching the earth’s surface change the climate. Several factors control the influx of solar energy, including (1) variations in the earth’s albedo, (2) variations in earth’s orbit and rotation, and (3) variations in solar energy output. In the short time since 1978, direct measurement of total solar irradiance (TSI) by satellites has shown cyclical variations in solar energy of 0.1% in conjunction with the 11-year sunspot cycle. Indirect evidence from the sun and other sunlike stars indicate that TSI has had significantly greater variation as the the sun goes through various cycles. The correlations between climate and TSI variations are statistically solid. Small variations in TSI initiate indirect mechanisms on earth that yield climate changes greater than that predicted for the TSI change alone. At least three solar variables are known to affect earth’s climate: (1) TSI, which directly affects temperatures; (2) solar unltraviolet radiation, which affects ozone production and upper atmospheric winds; and (3) solar wind, which affects rainfall and cloud cover, at least partially, through control of the earth’s electrical field. Each affects the earth’s climate in different ways, producing indirect effects that amplify small changes in TSI. Individually, they do not cause the entire observed climate changes. Collectively, they appear to be sufficient, especially because solar forcing of earth’s climate is still an emerging science. Undoubtedly, other mechanisms of solar forcing are poorly understood, perhaps even unknown.

Perspective: National Cancer Institute summary report about estimated exposures and thyroid doses received from iodine 131 in fallout after Nevada atmospheric nuclear bomb tests.

Environmental 131I contamination from atmospheric nuclear bomb tests conducted at the NTS from 1951 to 1958 exposed Americans nationwide to a cumulative average dose of 1 to 4 rad to the thyroid gland. By comparison, 10 years of exposure to natural background sources of thyroid radiation results in a cumulative dose of 1 rad. Americans living in certain high-deposition areas received an average cumulative thyroid dose of as much as 16 rad. Individual dose rates vary considerably as a function of age at the time of exposure, site of residence, and dietary habits with respect to milk consumption. The individual cumulative thyroid dose for persons born between 1945 and 1958 may be significantly higher than the reported averages for their locale. The NCI report contains voluminous data tables permitting detailed calculations of individual dose. Additionally, color-coded dose maps allow one to approximate individual dose conveniently. Translation of cumulative thyroid dose attributable to 131I to predictions of increased rates of thyroid cancer appears problematic and is the subject of further study. In contrast to studies of patients receiving external thyroid irradiation, existing studies of patients treated with 131I for diagnostic and therapeutic medical purposes do not document increased rates of thyroid cancer. An Institute of Medicine task force is expected to issue a report on this subject in September 1998. This review also briefly summarizes the evaluation, diagnosis, and treatment of patients with papillary and follicular thyroid cancers. Data from 53,856 patients with thyroid cancer accessioned to the NCDB from 1985 to 1995 document extremely high survival rates for patients in the United States with papillary and follicular thyroid cancer.

Lunar tides in the mesosphere over Christmas Island (2°N, 203°E)

This paper reports the first measurement of the lunar tide in upper atmosphere winds at an equatorial site. Wind velocities have been measured at Christmas Island, in the Pacific Ocean, from 1990 to 1993 over the height range 82 to 98 km and hourly values have been used to deduce the lunar tide using a least squares method. Amplitudes are 1 to 3 m/s with only small changes in phase with season. A large phase change over the early part of 1990 was found in the northward wind. Generally, the phase difference between northward and eastward winds was about 6 hours, and good agreement was obtained with a tidal model developed from that of Forbes [1982a].

Electrodynamic coupling effects in the thermosphere/ionosphere system

Thermospheric winds have a strong influence on the dynamics and electrodynamics of the ionosphere, and in return, ionospheric electrodynamic processes feed back onto the dynamics of the thermosphere. Observations of geomagnetic variations and ionospheric electric fields can provide valuable information about the distribution and variability of upper atmospheric winds systems, including atmospheric tides and planetary waves that propagate into the ionosphere from the middle atmosphere. The observations can lead to inferences about the generation and propagation conditions of those global waves in the lower and middle atmosphere, and hence provide information concerning changes in the state of the global atmosphere. Realistic simulation modeling of ionospheric electrodynamic effects must take into account the interactions between neutral and plasma dynamics, as is done in the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model. At low latitudes, the mutual coupling among neutral dynamics, ionospheric plasma dynamics, electrical conductivities, electric fields, and currents strongly affects the behavior of the thermosphere and ionosphere. At high latitudes, thermospheric and ionospheric phenomena are also strongly coupled to magnetospheric electrodynamics.

Upper atmosphere wind systems during reverse equatorial electrojet events

Days of reversed equatorial electrojet were identified at Trivandrum, India, and, in order to seek a global wind change in the dynamo region responsible for these events, upper atmosphere winds at a height of 99 km at Saskatoon, Canada, were examined. During northern winter, and also in April and September, the reversed electrojets were accompanied by reversals of the eastward wind at Saskatoon. The winter events generally occurred during a stratwarm. No changes in the winds were detected during summer reversed electrojets.

Application of Doppler Michelson imaging to upper atmospheric wind measurement: WINDII and beyond

A solid Doppler Michelson interferometer, consisting of different refractive plates cemented in the two arms of the interferometer, can be designed to be field widened, achromatic, and thermally stable. If the mirror in one arm is allowed to step over one wavelength about a fixed optical path difference, then phase-stepping interferometry can be used to determine the phase of an input spectral line. This is the basis of an optical Doppler interferometer used to measure upper atmospheric winds from space: the wind imaging interferometer (WINDII) on the Upper Atmosphere Research Satellite, UARS, which was launched on 12 September 1991 and is still operating in orbit. The instrument employs a CCD imager to record a sequence of images at different phase steps from which images of optical emission rate, wind, and temperature are derived. The WINDII concept is reviewed, and its implementation is described. The performance in orbit is then reviewed, and a summary of some of the geophysical results is given. Finally, some suggestions for future applications of this concept are presented.

ERWIN: an E-region wind interferometer

A field-widened Michelson interferometer designed to measure upper atmospheric winds at three altitudes near the mesopause by using airglow emissions from O(1)S, OH, and O(2) is described. A very large path difference (11 cm) is used to suppress the fringes from the hot F-region emission of O(1)S and to facilitate accurate measurements. Field widening and thermal compensation are achieved over the large spectral range (557.7-866.0 nm) by the use of three types of glass in the interferometer's arms. The instrument was installed at Resolute Bay, Canada (74.3 N, 94.5 W), in November 1992 and has been operated remotely from Toronto for four winter seasons. Some examples of data are shown to illustrate ERWIN's performance.

Observations of lunar tides in upper atmosphere winds at Poker Flat, Alaska

The lunar semidiurnal tide is extracted from hourly values of winds in the 75–105 km region measured by the Poker Flat Alaska MST radar used in the meteor mode. Since year-to-year variations are apparent, detailed results for 1983 and 1984 are presented. Inferred vertical wavelengths range from 17 km in March 1983 to 46–55 km in September of 1983 and 1984. The height progression of the phase is frequently too irregular to derive a vertical wavelength. Amplitudes of 3 m s −1 are common and range up to 8 m s −1. Amplitudes generally are largest at the equinoxes, especially in September, with another maximum in winter sometimes occurring. Reasonable agreement is found with lunar tidal measurements at Saskatoon, and some points of similarity are found with the solar semidiurnal tide at Poker Flat.

Lidar shows air at its most empty

In the past few weeks, National Oceanic and Atmospheric Administration atmospheric scientists have used lidar instruments trained on some of the cleanest air on Earth to measure what may be the global background concentration of aerosols in the atmosphere.The observations are part of an effort to determine if air at its most clear still contains sufficient numbers of aerosol particles to allow a planned satellite‐based lidar to use them to track upper atmospheric winds all over the world.

Orbit determination and analysis for Cosmos 482 from 1978 to 1981

The orbit of the satellite Cosmos 482 (1972-23A) has been determined at 77 epochs between 8 November 1977 and 18 April 1981 from 5650 optical and radar observations. The computations were made with the RAE orbit determination program PROP 6, and an average accuracy of 150 m radial and cross-track was achieved. Cosmos 482 was a high-drag satellite in an eccentric orbit and, between the first epoch and the last, the orbital period decreased from 157 to 94 min, the eccentricity decreased from 0.32 to 0.04, and the orbital inclination decreased from 52.14° to 51.95° due to the transverse forces caused by atmospheric rotation. The orbit was therefore ideal for determining the atmospheric rotation rate from the decrease in inclination, and seven accurate values of rotation rate have been obtained. The new values strengthen the existing overall picture of upper-atmosphere winds, and are generally in good accord with the previous results. An improved equation has been derived for calculating density scale height H from the decrease in perigee distance, and has been applied to determine seven values of H. The corresponding values of H from the COSPAR International Reference Atmosphere are on average 5% lower than the observational values, for 1980–1981.

Rocket Observations of Kelvin Waves in the Upper Stratosphere over India

Abstract The upper atmospheric winds (20–40 km) at two Indian stations, Sriharikota Range (SHAR 13.7°N, 80.2°E) and Balasore (2 1.5°N, 86.93°E) during the years 1979–80 were analyzed for short scale vertical variations (6–16 km) of the zonal wind. The analysis involves high-pass filtering of the wind profiles to extract the short-scale wavelike perturbations and Fourier analysis of the wave disturbances. The results of the analysis are presented. The dominant vertical wavelengths are in the 6–12 km range in 67% of the observed cases, and the amplitudes are significantly larger during the easterly background wind. The amplitudes are systematically larger by about a factor of 2 at Sriharikota (13.7°N) than at 1Wasore (21.5°N). Corresponding wave perturbations are absent in the meridional wind in as much as 70% of the observations. These characteristics lead to the conclusion that the observed wavelike disturbances are the manifestation of Kelvin waves in the upper stratosphere. In some cases, the periods of...

WAMDII: wide-angle Michelson Doppler imaging interferometer for Spacelab

A wide-angle Michelson Doppler imaging interferometer (WAMDII) is described that is intended to measure upper atmospheric winds and temperatures from naturally occurring visible region emissions, using Spacelab as a platform. It is an achromatic field-widened instrument, with good thermal stability, that employs four quarterwave phase-stepped images to generate full images of velocity, temperature, and emission rate. For an apparent emission rate of 5 kR and binning into 85 x 105 pixels, the required exposure time is 1 sec. The concept and underlying principles are described, along with some fabrication details for the prototype instrument. The results of laboratory tests and field measurements using auroral emissions are described and discussed.