TIMED Doppler Interferometer Research Articles

Seasonal variability of the diurnal tide in the mesosphere and lower thermosphere over Maui, Hawaii (20.7°N, 156.3°W)

[1] The seasonal variability of the diurnal tide in the mesosphere and lower thermosphere over Maui, Hawaii (20.7°N, 156.3°W), is investigated using meteor radar horizontal wind measurements from the years 2002 to 2007. The semiannual oscillation (SAO) of tidal amplitudes is dominant above ∼88 km, with amplitudes at equinoxes 2–3 times larger than at solstices. Below 88 km, the annual oscillation (AO) dominates, and its magnitude is smaller than the SAO. The AO dominates in the phase variation of the diurnal tide, which advances in winter and lags in summer as compared with equinoxes. The vertical wavelength also has a noticeable seasonal variation with shorter vertical wavelengths found at equinoxes. The reconstructed diurnal tide from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) Doppler interferometer (TIDI) and Sounding the Atmosphere using Broadband Emission Radiometry (SABER) measurements is compared with the meteor radar observation, and a consistency is found in the seasonal variation of the tidal amplitude. On the basis of the TIDI and SABER measurements, the migrating diurnal tide (DW1) is the dominant tidal component, while three other nonmigrating tides, DW2, DS0, and DE3, are nonnegligible. The seasonal variation of the diurnal tide is well captured by the global scale wave model and the Whole Atmosphere Community Climate Model, although important discrepancies still exist.

Mesospheric wind semidiurnal tides within the Canadian Middle Atmosphere Model Data Assimilation System

[1] The horizontal wind data from the standard version of Canadian Middle Atmosphere Model Data Assimilation System (CMAM-DAS) for the years 2006–2008 are analyzed to obtain the global structure and seasonal variability of the semidiurnal tide (SDT) in the mesosphere. The modeled amplitudes and phases of the SDTs at single stations from middle/high northern latitudes are quite similar to those observed by radars. The primary nonmigrating tides identified in both the meridional wind and zonal wind semidiurnal spectra at 88 km include the westward propagating wave numbers s = 1 (SW1), 3 (SW3), 4 (SW4), 6 (SW6), the standing s = 0 (S0), and the eastward propagating s = 2 (SE2). The migrating SDT (SW2) amplitude maxima usually occur at 40°N–60°N during December–February and August–September, and also at 40°S–60°S in April–May, with the dominance of (2, 4) during October–April and (2, 3) and (2, 5) dominance for other months. The CMAM-DAS is quite successful in reproducing the dominance of SW1 in the Antarctic summer mesosphere. The modeled SW1 shows very good overall agreement in both amplitude and phase with wind measurements from UARS High Resolution Doppler Imager and Wind Imaging Interferometer (UARS-HRDI/WINDII) and from TIMED Doppler Interferometer (TIDI). The CMAM-DAS analyses for SW3, SW4, SW6, and S0 are also in reasonable agreement with those determined from the HRDI/WINDII or TIDI wind measurements. This work provides further evidence for the tidal forcing from below.

Meteor radar measurements of MLT winds near the equatorial electro jet region over Thumba (8.5° N, 77° E): comparison with TIDI observations

Abstract. The All-Sky interferometric meteor (SKYiMET) radar (MR) derived winds in the vicinity of the equatorial electrojet (EEJ) are discussed. As Thumba (8.5° N, 77° E; dip lat. 0.5° N) is under the EEJ belt, there has been some debate on the reliability of the meteor radar derived winds near the EEJ height region. In this regard, the composite diurnal variations of zonal wind profiles in the mesosphere-lower thermosphere (MLT) region derived from TIMED Doppler Interferometer (TIDI) and ground based meteor radar at Thumba are compared. In this study, emphasis is given to verify the meteor radar observations at 98 km height region, especially during the EEJ peaking time (11:00 to 14:00 LT). The composite diurnal cycles of zonal winds over Thumba are constructed during four seasons of the year 2006 using TIDI and meteor radar observations, which showed good agreement especially during the peak EEJ hours, thus assuring the reliability of meteor radar measurements of neutral winds close to the EEJ height region. It is evident from the present study that on seasonal scales, the radar measurements are not biased by the EEJ. The day-time variations of HF radar measured E-region drifts at the EEJ region are also compared with MR measurements to show there are large differences between ionospheric drifts and MR measurements. The significance of the present study lies in validating the meteor radar technique over Thumba located at magnetic equator by comparing with other than the radio technique for the first time.

Verification of large-scale rapid transport in the lower thermosphere: Tracking the exhaust plume of STS-107 from launch to the Antarctic

[1] New analysis of the Doppler shift of O2 airglow spectra recorded by the TIMED Doppler Interferometer (TIDI) and the High Resolution Doppler Imager (HRDI) have provided conclusive evidence that the shuttle main engine exhaust plume generated in the lower thermosphere by the launch of STS-107 and imaged by the Global Ultraviolet Imager (GUVI) instrument on TIMED was transported to the Antarctic in ∼80 h, supporting a key inference from the initial study by Stevens et al. (2005). These new results were aided by improved knowledge of the effects of instrumental and satellite artifacts imposed on the Doppler spectra. STS-107 launched on 16 January 2003, and the neutral wind near its launch trajectory and nearby volume was sampled within minutes by TIDI. These initial observations suggested that the northernmost end of the shuttle's exhaust plume would move northeast and that the southern end would move southeast, motions that were identified in imagery acquired during the next orbit of TIMED. The direction and magnitude of plume motion inferred from GUVI images obtained 12, 26, and 50 h after launch were again confirmed by TIDI and HRDI. The appearance of the plume over the Antarctic ∼80 h after launch, inferred from earlier work by the appearance of iron ablated from the shuttle's main engines, was consistent with neutral winds measured by the satellite Doppler instruments over the Antarctic. The transport of the plume from the coast of Florida to the Antarctic was aided by the favorable phase and strong amplitude of a 2 day planetary wave of wave number three in the southern hemisphere on 18 January 2003. The existence of the 2 day wave was deduced from zonally averaged and combined TIDI and HRDI neutral wind observations. We conclude that the existence of strong and sustained winds in the MLT, significantly greater than expected from empirical and theoretical models, is indisputable and provides compelling evidence supporting the global-scale nature of thermospheric winds with magnitude greater than 100 m/s observed by Larsen (2002) from 40 years of sounding rocket chemical release experiments.

Momentum budget of the migrating diurnal tide in the mesosphere and lower thermosphere

The leading terms of the momentum budget of the migrating diurnal tide are diagnosed from temperatures and geopotential height provided by Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics (TIMED)/Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) and the horizontal wind vector provided by TIMED Doppler Interferometer (TIDI). The “wave drag” upon the tide is inferred as a residual of the classical and linear advective terms in the zonal and meridional momentum equations. Between 85 and 100 km, the migrating diurnal tide is generally far from the classical description of Chapman and Lindzen (1970). The leading nonclassical terms are the meridional advection of zonally averaged momentum and wave drag effects encapsulated in the momentum residuals. The magnitudes of the momentum residuals range between 50 and 150 m s−1 d−1 for the zonal component and 100–250 m s−1 d−1 for the meridional component. The zonal momentum residual is generally in quadrature with the zonal wind tide, while the meridional momentum residual is in antiphase with the meridional wind above 95 km. Winds and temperatures exhibit maximum amplitudes during the vernal equinox season, but only a minor reduction in wave damping is observed. Our results suggest that Rayleigh damping is inadequate to describe the relationship between the tide and the forces acting upon it.

Simulated wave number 4 structure in equatorial F‐region vertical plasma drifts

This article investigates the wave number 4 longitudinal structure in equatorial vertical E × B plasma drifts (V⊥), using the Theoretical Ionospheric Dynamo Model, Institute of Geology and Geophysics, Chinese Academy of Sciences, Version II model and the DE3 tide wind from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED)/TIMED Doppler interferometer (TIDI) observations. We simulate this longitudinal structure and examine its intra‐annual variations and the effect of different DE3 tide components and of different current components on it. We find that this longitudinal structure shows obvious intra‐annual variation, being strongest in northern summer and autumn and weakest in northern winter. This result is consistent with the intra‐annual variation observed by Ren et al. (2009b). Our simulations also suggest that the eastward propagation of the DE3 tide can cause the eastward shift of the wave number 4 structure in V⊥. The wave number 4 structures in V⊥ are mainly driven by a zonal wind component of DE3 tide, which contributes much more than the meridional wind component of DE3 tide to the wave number 4 structure in V⊥. With the influence of the coupling of ionospheric electric fields along the highly conducting magnetic field lines, the symmetric wind component of DE3 tide plays a more important role in the wave number 4 structure in V⊥ than the antisymmetric component does. The intra‐annual variations of the wave number 4 structure in V⊥ are mainly controlled by the symmetric wind component of DE3 tide. Our simulations also suggest that the wave number 4 structures in V⊥ are mainly driven by the Hall current.

Nonmigrating semidiurnal tide over the Arctic determined from TIMED Doppler Interferometer wind observations

The TIMED Doppler Interferometer (TIDI) on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite has been measuring horizontal winds in the mesosphere and lower thermosphere (MLT) since 2002. Because of the high inclination of the TIMED orbit, TIDI measures the horizontal winds from pole to pole every orbit. This paper presents the first assessment of the spatial structure and temporal evolution of the nonmigrating semidiurnal tides over the Arctic determined from the TIDI wind measurements and a comparison of the structure of the nonmigrating semidiurnal tide between the Arctic and Antarctic. The nonmigrating semidiurnal tides were determined as a 60 day average based on the yaw cycles of the spacecraft. The nonmigrating semidiurnal tidal wind field over the Arctic comprises mainly the westward‐propagating zonal wave numbers 1 (W1) and 3 (W3) and standing zonal wave number 0 (S0) modes. The W1 mode is the most prominent, maximizing above 90 km poleward of 60°N during the yaw interval ranging from mid‐March to mid‐May. While this mode exhibits a slight amplitude increase toward the North Pole during this interval, its phase is nearly constant with latitude. The S0 mode is enhanced over two yaw intervals ranging from mid‐January to mid‐May, but its amplitude decreases toward the North Pole. Compared to the W1 semidiurnal tide over the Antarctic, that over the Arctic is smaller in amplitude, of less extended duration, achieves maximum amplitudes at higher altitudes by ∼10 km, and exhibits a weaker amplitude increase toward the pole. These differences likely result from differences in excitation mechanisms and efficiency and/or in propagation conditions in the two responses for the nonmigrating semidiurnal tides between the Arctic and Antarctic.

Seasonal and quasi‐biennial variations in the migrating diurnal tide observed by Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED)

We present periodic variations of the migrating diurnal tide from Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) temperature and wind data from 2002 to 2007 and meteor radar data at Maui (20.75°N, 156.43°W). There are strong quasi‐biennial oscillation (QBO) signatures in the amplitude of the diurnal tidal temperature in the tropical region and in the wind near ±20°. The magnitude of the QBO in the diurnal tidal amplitude reaches about 3 K in temperature and about 7 m/s (Northern Hemisphere) and 9 m/s (Southern Hemisphere) in meridional wind. The period of the diurnal tide QBO is around 24–25 months in the mesosphere but is quite variable with altitude in the stratosphere. Throughout the mesosphere, the amplitude of the diurnal tide reaches maximum during March/April of years when the QBO in lower stratospheric wind is in the eastward phase. Because the tide shows amplification only during a limited time of the year, there are not enough data yet to determine whether the tidal variation is truly biennial (24‐month period) or is quasi‐biennial. The semiannual (SAO) and annual oscillations (AO) in the diurnal tide support previous findings: tidal amplitude is largest around equinoxes (SAO signal) and is larger during the vernal equinox (AO signal). TIMED Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER) temperature and atmospheric pressure data are used to calculate the balance wind and the tides in horizontal wind. The comparison between the calculations and the wind observed by TIMED Doppler Interferometer (TIDI) and meteor radar indicates qualitative agreement, but there are some differences as well.

Structure of the nonmigrating semidiurnal tide above Antarctica observed from the TIMED Doppler Interferometer

Spatial structure and temporal evolution of the nonmigrating semidiurnal tidal components over Antarctica are determined by analyzing horizontal wind measurements in the Mesosphere and Lower Thermosphere (MLT) collected using TIMED Doppler Interferometer (TIDI) on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite from 2002 to 2007. The data were organized into six specific intervals of approximately 60 days corresponding to the TIMED yaw periods. The results confirm the existence of a westward propagating zonal wave number 1 (W1) semidiurnal tidal component in the Antarctic MLT meridional wind field prior to the Austral summer solstice. This wave achieves a peak amplitude near 20 m s−1 at 90 km and is vertically stratified while extending latitudinally from the pole to 60°S. A similar structure is observed in the zonal wind field. However, the amplitude maximizes around the Austral summer solstice during the yaw period spanning 15 November to 15 January. In addition to a strong latitudinal gradient in amplitude, the W1 component also shows a vertical wavelength from 20 km near the pole to 40 km at 60°S. The amplitude and phase agree well with ground‐based meteor radar observations from the South Pole. Evidence for significant though weaker standing (S0) and W3 components is also found. These components diminish in the vicinity of the pole and appear during the winter months with latitudinally restricted structures. The vertical wavelength of the S0 component during the summer is 25 km, similar to the W1 component. During the winter the wavelength of the S0 component becomes nearly evanescent.

Global distribution and interannual variations of mesospheric and lower thermospheric neutral wind diurnal tide: 1. Migrating tide

Using the TIMED Doppler interferometer (TIDI) mesospheric and lower thermospheric neutral‐wind multiyear data set (2002–2007) and NCAR TIME General Circulation Models (GCM) 1.2 annual run results (2002–2005) at the TIDI sampling points, we study the migrating diurnal tide's global distribution, interannual, and seasonal variations in connection with the mean zonal wind interannual variations. A strong quasi‐biennial oscillation (QBO) effect on the diurnal tide was observed in the TIDI data and reproduced to a lesser degree in the TIME‐GCM run. The migrating diurnal tide amplitude is larger during the eastward phase of the stratospheric QBO and weaker during the westward phase. Westward mesospheric equatorial mean zonal winds appeared during the eastward phase of the stratospheric QBO (in 2002, 2004, and 2006). The strongest QBO effect on both the migrating diurnal tide and mean zonal winds was observed during the March equinox. The stronger tides may be related to the weaker gravity wave filtering in the stratosphere during the eastward phase stratospheric QBO. The TIDI data also exhibit large interhemispheric asymmetry. The westward mean zonal winds in the mesosphere appeared to be associated with the enhanced diurnal tide. The TIME‐GCM 1.2 diurnal tide amplitudes are in general smaller than those observed by the TIDI instrument. Limited vertical spatial resolution for the TIME‐CGM 1.2 is suggested as the cause. Future improvements are expected with a higher spatial resolution in the model.

The 5-8-Day Kelvin and Rossby Waves in the Tropics as Revealed by Ground and Satellite-Based Observations

An eastward propagating Kelvin wave of period near 7 days is observed in the radiosonde winds and temperature in the upper troposphere and lower stratosphere (UTLS) region and a wave of similar periodicity is observed simultaneously in the Mesosphere and Lower Thermosphere (MLT) winds acquired by MF radar at Pameungpeuk (7.5°S, 107.5°E) during the first Coupling Processes in the Equatorial Atmosphere (CPEA-1) Campaign (April 10-May 9, 2004). The horizontal and vertical characteristics of these waves are investigated using winds and temperature data acquired by TIDI (TIMED Doppler Interferometer) and Sounding of Atmosphere using Broadband Emission Radiometry (SABER) instruments respectively on TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics) satellite and European Centre for Medium-Range Weather Forecasts (ECMWF) winds and temperature. The wave observed in the MLT region has a dominant period of approximately 6.5 days and is found to propagate westward with zonal wave number 1. The horizontal structures of the wave in winds and the temperature indicate that the wave is of gravest symmetric wave number 1 Rossby wave. The downward phase propagation from the MLT region to tropopause indicates that the wave may have a source in the troposphere. The Kelvin wave observed in the UTLS region has zonal wave number 3. However, this wave becomes damped above 23 km, where the above mentioned westward propagating wave begins to amplify. During the observation period, the OLR distribution in the tropics shows similar periodicities, propagating eastward with zonal wave number 3 and westward with zonal wave number 1. These observations suggest that tropical convective heating may be a common source for these waves.

Comparative study of short‐term diurnal tidal variability

The wind and temperature measurements from an unusually long period operation of the sodium lidar at Colorado State University (41°N, 105°W) around September equinox 2003 showed significant short‐term tidal variability. Coincident with the large tidal changes, a strong temperature inversion layer was also observed above 90 km. Examination of the simultaneous temperature measurement from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite, not only confirms the existence of the inversion layer but also reveals the global nature of the inversion, suggesting the presence of a transient planetary wave in the mesosphere. The large tidal variability, therefore, is probably a consequence of the interaction between the transient planetary wave and tides. This possibility is investigated by using the NCAR thermosphere‐ionosphere‐mesosphere‐electrodynamics general circulation model (TIME‐GCM) and by comparing model results with the lidar, SABER, and TIMED Doppler Interferometer (TIDI) measurements. With a large transient planetary wave specified at the model lower boundary, the model is able to produce strong diurnal tidal variability comparable to that from the lidar observation, and the modeled temperature inversion is similar to that from the SABER measurement. The model results suggest that the planetary/tidal wave interaction excites nonmigrating tides and modulates the gravity modes and/or the rotational modes of the diurnal migrating tide. Among the nonmigrating tides, the diurnal zonally symmetric (S = 0) component is the strongest, and its interaction with the planetary wave leads to a strong diurnal eastward wave number 1 component.

Semidiurnal tides from the extended Canadian Middle Atmosphere Model (CMAM) and comparisons with TIMED Doppler interferometer (TIDI) and meteor radar observations

The extended Canadian Middle Atmosphere Model (extended CMAM) is a general circulation model, which extends from the surface to about 210 km. Spatial complex spectral analysis is applied to horizontal winds simulated by the extended CMAM to obtain semidiurnal tidal amplitudes and phases (from e5 to w5) in the mesosphere and lower thermosphere (MLT) region. The dominant w2 migrating component and the presence of eight nonmigrating tides (w3, w4, w5, e1, e2, e3, e4 and e5) in the mid-latitudes are identified. Components w1 and s0, which tend to maximize at high latitudes, will be discussed separately in a later paper. The migrating semidiurnal tide (w2) has amplitudes reaching over 20 m s −1 for both zonal and meridional winds in the mid-latitude region. Its form compares well to the published results. The amplitudes of nonmigrating semidiurnal tides are non-negligible compared with the migrating semidiurnal tides. The amplitudes for w3 and e2 exceed 12 and 8 m s −1, respectively. Comparisons are made with four nonmigrating semidiurnal components (w3, w4, e1 and e2) derived from the TIMED Doppler interferometer (TIDI) wind measurements between 85 and 105 km altitude and between 45°S and 45°N latitude. Overall, the basic CMAM and TIDI latitudinal structures of the amplitudes agree well and the agreement between the annual mean amplitudes varies with component. Relative to the TIDI results, the CMAM seasonal variations of w4 are in good agreement, of e2 are in reasonable agreement, of w3 are in partial agreement and of e1 are in poor agreement. The 11 semidiurnal components from the model are superimposed to generate the total semidiurnal winds at Jakarta (6°S, 106°E) and Kototabang (0°, 100°E) and are compared with measurements from two equatorial meteor radar stations at these sites. The relative contributions of components to the reconstructed amplitude vary from month to month. The CMAM reconstructions are generally larger than the radar results by a factor varying between one and two. The phases in the radar data are typically stationary with respect to height, whereas they generally decrease with height in the CMAM reconstruction.

Mesospheric doppler wind measurements from Aura Microwave Limb Sounder (MLS)

This paper describes a microwave limb technique for measuring Doppler wind in the Earth’s mesosphere. The research algorithm has been applied to Aura Microwave Limb Sounder (MLS) 118.75 GHz measurements where the O 2 Zeeman lines are resolved by a digital autocorrelation spectrometer. A precision of ∼17 m/s for the line-of-sight (LOS) wind is achieved at 80–92 km, which corresponds to radiometric noise during 1/6 s integration time. The LOS winds from Aura MLS are mostly in the meridional direction at low- and mid-latitudes with vertical resolution of ∼8 km. This microwave Doppler technique has potential to obtain useful winds down to ∼40 km of the Earth’s atmosphere if measurements from other MLS frequencies (near H 2O, O 3, and CO lines) are used. Initial analyses show that the MLS winds from the 118.75 GHz measurements agree well with the TIDI (Thermosphere Ionosphere Mesosphere Energetics and Dynamics Doppler Interferometer) winds for the perturbations induced by a strong quasi 2-day wave (QTDW) in January 2005. Time series of MLS winds reveal many interesting climatological and planetary wave features, including the diurnal, semidiurnal tides, and the QTDW. Interactions between the tides and the QTDW are clearly evident, indicating possible large tidal structural changes after the QTDW events dissipate.

A climatology of nonmigrating semidiurnal tides from TIMED Doppler Interferometer (TIDI) wind data

With the launch of the TIMED satellite in December 2001, continuous temperature and wind data sets amenable to MLT tidal analyses became available. The wind measuring instrument, the TIMED Doppler Interferometer (TIDI), is operating since early 2002. Its day- and nighttime capability allows to derive tidal winds over a range of MLT altitudes. This paper presents climatologies (June 2002–June 2005) of monthly mean amplitudes and phases for six nonmigrating semidiurnal tidal components between 85 and 105 km altitude and between 45°S and 45°N latitude (westward propagating wave numbers 4, 3, 1; the standing oscillation s0; and eastward propagating wave numbers 1, 2) in the zonal and meridional wind directions. Amplitude errors are 15–20% (accuracy) and 0.8 m/s (precision). The phase error is 2 h. The TIDI analysis agrees well with 1991–1994 UARS results at 95 km. During boreal winter, amplitudes of a single component can reach 10 m/s at latitudes equatorward of 45°. Aggregate effects of nonmigrating tides can easily reach or exceed the amplitude of the migrating tide. Comparisons with the global scale wave model (GSWM) and the thermosphere–ionosphere–mesosphere–electrodynamics general circulation model (TIME-GCM) are partly inconclusive but they suggest that wave–wave interaction and latent heat release in the tropical troposphere both play an important role in forcing the semidiurnal westward 1, westward 3, and standing components. Latent heat release is the leading source of the eastward propagating components.

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.

Diurnal nonmigrating tides from TIMED Doppler Interferometer wind data: Monthly climatologies and seasonal variations

TIMED Doppler Interferometer (TIDI) measurements of zonal and meridional winds in the mesosphere/lower thermosphere are analyzed for diurnal nonmigrating tides (June 2002 to June 2005). Climatologies of monthly mean amplitudes and phases for seven tidal components are presented at altitudes between 85 and 105 km and latitudes between 45°S and 45°N (westward propagating wave numbers 2, 3, and 4; the standing diurnal tide; and eastward propagating wave numbers 1, 2, and 3). The observed seasonal variations agree well with 1991–1994 UARS results at 95 km. Comparisons between the TIDI results and global scale wave model (GSWM) and thermosphere‐ionosphere‐mesosphere‐electrodynamics general circulation model (TIME‐GCM) tidal predictions indicate that the large eastward propagating wave number 3 amplitude is driven by tropical tropospheric latent heat release alone. In contrast, latent heating and planetary wave/migrating tidal interactions are equally important to westward 2 and standing diurnal tidal forcing. There is good quantitative agreement between TIDI and the model predictions during equinox, but the latter tend to underestimate the westward 2 and standing diurnal tide during solstice. Neither model reproduces the observed seasonal variations of the eastward propagating components.

TIMED Doppler interferometer (TIDI) observations of migrating diurnal and semidiurnal tides

Based on zonally averaged TIDI meridional wind data from one yaw period (March 19–May 19, 2004) near equinox, we examine the latitudinal and altitudinal distribution of the migrating diurnal and semidiurnal tides using least-squares fitting method to provide a global view of these tidal waves. The TIDI results are compared with Global Scale Wave Model 00 output for the month of April. The diurnal tide amplitude distribution are in a good agreement in the northern hemisphere and differ in amplitude in the southern hemisphere. The TIDI results show a lower peak altitude (97 km), while GSWM00 peaks at 102 km.The peak latitudes for the diurnal tide are at 20°N and 20°S for both the TIDI data and GSWM00 model. The TIDI data seem to show that the amplitude of the diurnal tide stronger in the northern hemisphere than in the southern hemisphere based on least-squares fitting results over the yaw period. The visually estimated vertical wavelength from the TIDI is about 20 km, while least-square fit results over the yaw period provided longer vertical wavelengths in northern (∼40 km) and southern hemisphere (∼30 km). We suspect that the seasonal change in the tide may cause the larger vertical wavelength. The GSWM00 provides a vertical wavelength of ∼26 km for the two hemispheres. Both model and TIDI data show semidiurnal tide peak amplitudes at 45° latitude. The measured semidiurnal tide peaked at lower altitudes (102 km in the southern hemisphere and 105 km in the northern hemisphere), whereas the GSWM00 shows peak altitudes at 110 km or above. The phases for the semidiurnal tide show a good agreement between the data and the GSWM00 model. The TIDI meridional winds are compared with ground based meteor radar measurements at Maui. The meteor data show smaller diurnal tide amplitude than that shown in the TIDI data. The phases of the diurnal tide appear to be consistent between the two data sets.

Non-migrating diurnal tides as measured by the TIMED Doppler interferometer: Preliminary results

Preliminary meridional wind data from the TIMED Doppler Interferometer (TIDI) onboard the TIMED satellite are analyzed for nonmigrating diurnal tides. Tidal definitions are given for the most pronounced westward, eastward and standing oscillations (w2, e3, s0). The analysis interval is March 2002 to June 2004 and covers the altitude range 85-105 km. Monthly tidal wind fields from 40 � S-40 � N are presented. TIDI tides compare favorably with previously reported 95 km HRDI results. Nonmigrating diurnal tidal wind speeds larger than 30 m/s are observed thus emphasizing the important role of nonmigrating tides in middle atmosphere coupling. A comparative analysis with the Global Scale Wave Model (GSWM) and the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM) indicates that both latent heat release in the tropical troposphere and non-linear Planetary Wave / migrating tide interaction are important sources of nonmigrating tides in the mesosphere and lower thermosphere.