Zonal mean and tidal dynamics from space: an empirical examination of aliasing and sampling

Abstract. Interpretations of space-based measurements of atmospheric parameters in the mesosphere and thermosphere are complicated by large local-time variations at these altitudes. For this reason, satellite orbits are often preferred which precess through all local times one or more times per season. However, the local-time structure of the atmosphere is inherently non-stationary, which can lead to sampling and aliasing difficulties when attempting to deconvolve the measurements into zonal mean and tidal components. In the present study, hourly radar measurements of mesopause-region winds are used to form a mock data base which can be used to gain insight into implications of the aforementioned problems; the use of actual measurements introduces a realistic element of geophysical temporal variability. Assuming zonal symmetry (i.e., migrating tides superimposed on a zonal mean circulation), the radar measurements are sampled from the satellite perspective for orbital inclinations of 57° and 70°, and compared to the ground or true perspective. These comparisons provide realistic estimates of the errors to be expected when attempting to derive mean and tidal components from space-based measurements. For both diurnal and semidiurnal components, and the quoted satellite inclinations, acceptable errors (3–4m/srms) are obtained for data covering 24h local time (i.e., ascending plus descending nodes); the corresponding errors for single-node data (12h local-time coverage) are of order 8–11m/s, and therefore may not represent reliable estimates of the actual tidal components. There exist certain caveats in connection with the latter conclusion which are discussed.

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Global nighttime atomic oxygen abundances from resampled GOMOS hydroxyl airglow measurements in the mesopause region

10.5194/acp-2019-417 ◽

2019 ◽

Author(s):

Qiuyu Chen ◽

Martin Kaufmann ◽

Yajun Zhu ◽

Jilin Liu ◽

Ralf Koppmann ◽

...

Keyword(s):

Atomic Oxygen ◽

Local Times ◽

Local Thermal Equilibrium ◽

Mesopause Region ◽

Mean Values ◽

Density Peaks ◽

Time Period ◽

Hydroxyl Airglow ◽

Non Local ◽

Insight Into

Abstract. This paper presents a new dataset of nighttime atomic oxygen density [O], derived from OH(8–4) ro-vibrational band emissions, using a non-local thermal equilibrium model, with the aim of offering new insight into the atomic oxygen abundances in the mesopause region. The dataset is based on the level-1 atmospheric background measurements observed by the GOMOS instrument on board Envisat. Raw data are reprocessed into monthly zonal mean values in 10° latitude bins with a fixed altitude grid of 3 km. The dataset spans from 70° S to 70° N in latitude and from 80 km to 100 km in altitude, covering a time period from May 2002 to December 2011 at local times of from 10 p.m. to 12 p.m. The atomic oxygen density peaks at about 95 km and the highest values are in the range of 3–8 × 1011 atoms cm−3, depending on latitude and season. There is a rapid decrease of [O] below its peak region. The annual oscillation (AO), semiannual oscillation (SAO), and the solar cycle impact are distinguished from the [O] longtime series variations. This new GOMOS [O] dataset conforms to other published datasets and is consistent with the [O] datasets obtained from the SCIAMACHY OH airglow measurements to within about ±20 %.

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Solar Backscatter UV (SBUV) total ozone and profile algorithm

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-5-5913-2012 ◽

2012 ◽

Vol 5 (4) ◽

pp. 5913-5951 ◽

Cited By ~ 18

Author(s):

P. K. Bhartia ◽

R. D. McPeters ◽

L. E. Flynn ◽

S. Taylor ◽

N. A. Kramrova ◽

...

Keyword(s):

Local Time ◽

Cross Sections ◽

Total Ozone ◽

Satellite Orbits ◽

Current Version ◽

Short Term ◽

Basic Algorithm ◽

Ozone Absorption ◽

Different Types ◽

Time Variations

Abstract. We describe the algorithm that has been applied to develop a 41 yr time series of total ozone and ozone profiles from eight solar-backscatter UV (sbuv) instruments launched on NASA and NOAA satellites since April 1970. Although the basic algorithm is similar to the V8 algorithm that was released about a decade ago and has been in use since then at NOAA, the details of the V8 algorithm have never been published. The current version (V8.6) incorporates several changes including the use of new ozone absorption cross-sections and new ozone and cloud height climatologies. A particular emphasis in this paper is on characterizing the sources of errors that are relevant for deriving trends from monthly mean anomalies and for estimating biases between different types of ozone sensors. We show that variations in the local time of the measurement due to drifting NOAA satellite orbits can complicate the analysis of trends in the upper stratosphere. Such variations not only increase instrumental and algorithmic uncertainties but also require correction for true local time variations of ozone in the upper stratosphere and lower mesosphere for trend analysis. We find that the monthly zonal anomalies derived from the SBUV data have high precision, sufficient to track year-to-year changes in ozone over a broad range of altitudes. However, because of poor vertical resolution the data are less well suited to track short-term variability of ozone at lower altitudes.

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Representations of hermite processes using local time of intersecting stationary stable regenerative sets

Journal of Applied Probability ◽

10.1017/jpr.2020.57 ◽

2020 ◽

Vol 57 (4) ◽

pp. 1234-1251

Author(s):

Shuyang Bai

Keyword(s):

Long Range ◽

Local Time ◽

Limit Theorems ◽

Local Times ◽

Long Range Dependence ◽

Random Interval ◽

Stationary Increments ◽

Self Similar ◽

Regenerative Sets

AbstractHermite processes are a class of self-similar processes with stationary increments. They often arise in limit theorems under long-range dependence. We derive new representations of Hermite processes with multiple Wiener–Itô integrals, whose integrands involve the local time of intersecting stationary stable regenerative sets. The proof relies on an approximation of regenerative sets and local times based on a scheme of random interval covering.

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King-Hele orbit theory for periodic orbit and attitude variations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3630 ◽

2020 ◽

Vol 501 (1) ◽

pp. 1168-1187

Author(s):

Vishal Ray ◽

Daniel J Scheeres

Keyword(s):

Drag Coefficient ◽

Dynamic Parameter ◽

Mission Design ◽

Fourier Series Expansion ◽

Satellite Orbits ◽

Physical Interaction ◽

Satellite Mission ◽

Simplifying Assumptions ◽

Time Variations ◽

Specific Factors

ABSTRACT The analytical theory of satellite orbits in an atmosphere developed by King-Hele remains widely in use for satellite mission design because of its accurate approximation to numerical integration under simplifying assumptions. Over the course of six decades, modifications to the theory have addressed many of its weaknesses. However, in all subsequent modifications of the original theory, the assumption of a constant drag-coefficient has been retained. The drag-coefficient is a dynamic parameter that governs the physical interaction between the atmosphere and the satellite and depends on ambient as well as satellite specific factors. In this work, Fourier series expansion models of the drag-coefficient are incorporated in the original King-Hele theory to capture time-variations of the drag-coefficient in averaging integrals. The modified theory is validated through simulations that demonstrate the attained improvements in approximating numerical results over the original King-Hele formulation.

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Cluster observation of few-hour-scale evolution of structured plasma in the inner magnetosphere

Annales Geophysicae ◽

10.5194/angeo-31-1569-2013 ◽

2013 ◽

Vol 31 (9) ◽

pp. 1569-1578 ◽

Cited By ~ 6

Author(s):

M. Yamauchi ◽

I. Dandouras ◽

H. Rème ◽

R. Lundin ◽

L. M. Kistler

Keyword(s):

Local Time ◽

Trapped Ions ◽

Low Energy ◽

Local Times ◽

Significant Enhancement ◽

Occurrence Rate ◽

Wide Energy Range ◽

Inner Magnetosphere ◽

Wide Energy ◽

Cluster Ion

Abstract. Using Cluster Ion Spectrometry (CIS) data from the spacecraft-4 perigee traversals during the 2001–2006 period (nearly 500 traversals after removing those that are highly contaminated by radiation belt particles), we statistically examined the local time distribution of structured trapped ions at sub- to few-keV range as well as inbound–outbound differences of these ion signatures in intensities and energy–latitude dispersion directions. Since the Cluster orbit during this period was almost constant and approximately north–south symmetric at nearly constant local time near the perigee, inbound–outbound differences are attributed to temporal developments in a 1–2 h timescale. Three types of structured ions at sub- to few keV range that are commonly found in the inner magnetosphere are examined: – Energy–latitude dispersed structured ions at less than a few keV, – Short-lived dispersionless ion stripes at wide energy range extending 0.1–10 keV, – Short-lived low-energy ion bursts at less than a few hundred eV. The statistics revealed that the wedge-like dispersed ions are most often observed in the dawn sector (60% of traversals), and a large portion of them show significant enhancement during the traversals at all local times. The short-lived ion stripes are predominantly found near midnight, where most stripes are significantly enhanced during the traversals and are associated with substorm activities with geomagnetic AL < −300 nT. The low-energy bursts are observed at all local times and under all geomagnetic conditions, with moderate peak of the occurrence rate in the afternoon sector. A large portion of them again show significant enhancement or decay during the traversals.

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New results on equatorial thermospheric winds and temperatures from Ethiopia, Africa

Annales Geophysicae ◽

10.5194/angeo-35-333-2017 ◽

2017 ◽

Vol 35 (2) ◽

pp. 333-344 ◽

Cited By ~ 10

Author(s):

Fasil Tesema ◽

Rafael Mesquita ◽

John Meriwether ◽

Baylie Damtie ◽

Melessew Nigussie ◽

...

Keyword(s):

Local Time ◽

Zonal Wind ◽

Meridional Wind ◽

Local Times ◽

Maximum Speed ◽

Wind Speeds ◽

Early Evening ◽

Meridional Winds ◽

Thermospheric Winds ◽

Wind Surge

Abstract. Measurements of equatorial thermospheric winds, temperatures, and 630 nm relative intensities were obtained using an imaging Fabry–Perot interferometer (FPI), which was recently deployed at Bahir Dar University in Ethiopia (11.6° N, 37.4° E, 3.7° N magnetic). The results obtained in this study cover 6 months (53 nights of useable data) between November 2015 and April 2016. The monthly-averaged values, which include local winter and equinox seasons, show the magnitude of the maximum monthly-averaged zonal wind is typically within the range of 70 to 90 ms−1 and is eastward between 19:00 and 21:00 LT. Compared to prior studies of the equatorial thermospheric wind for this local time period, the magnitude is considerably weaker as compared to the maximum zonal wind speed observed in the Peruvian sector but comparable to Brazilian FPI results. During the early evening, the meridional wind speeds are 30 to 50 ms−1 poleward during the winter months and 10 to 25 ms−1 equatorward in the equinox months. The direction of the poleward wind during the winter months is believed to be mainly caused by the existence of the interhemispheric wind flow from the summer to winter hemispheres. An equatorial wind surge is observed later in the evening and is shifted to later local times during the winter months and to earlier local times during the equinox months. Significant night-to-night variations are also observed in the maximum speed of both zonal and meridional winds. The temperature observations show the midnight temperature maximum (MTM) to be generally present between 00:30 and 02:00 LT. The amplitude of the MTM was ∼  110 K in January 2016 with values smaller than this in the other months. The local time difference between the appearance of the MTM and a pre-midnight equatorial wind was generally 60 to 180 min. A meridional wind reversal was also observed after the appearance of the MTM (after 02:00 LT). Climatological models, HWM14 and MSIS-00, were compared to the observations and the HWM14 model generally predicted the zonal wind observations well with the exception of higher model values by 25 ms−1 in the winter months. The HWM14 model meridional wind showed generally good agreement with the observations. Finally, the MSIS-00 model overestimated the temperature by 50 to 75 K during the early evening hours of local winter months. Otherwise, the agreement was generally good, although, in line with prior studies, the model failed to reproduce the MTM peak for any of the 6 months compared with the FPI data.

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Temperature decadal trends, and their relation to diurnal variations in the lower thermosphere, stratosphere, and mesosphere, based on measurements from SABER on TIMED

Annales Geophysicae ◽

10.5194/angeo-39-327-2021 ◽

2021 ◽

Vol 39 (2) ◽

pp. 327-339

Author(s):

Frank T. Huang ◽

Hans G. Mayr

Keyword(s):

Local Time ◽

Lower Thermosphere ◽

3D Models ◽

Diurnal Variations ◽

Local Times ◽

Temperature Trends ◽

Microwave Sounding Unit ◽

Lidar Measurements ◽

Microwave Sounding ◽

Thermal Tides

Abstract. We have derived the behavior of decadal temperature trends over the 24 h of local time, based on zonal averages of SABER data, for the years 2012 to 2014, from 20 to 100 km, within 48∘ of the Equator. Similar results have not been available previously. We find that the temperature trends, based on zonal mean measurements at a fixed local time, can be different from those based on measurements made at a different fixed local time. The trends can vary significantly in local time, even from hour to hour. This agrees with some findings based on nighttime lidar measurements. This knowledge is relevant because the large majority of temperature measurements, especially in the stratosphere, are made by instruments on sun-synchronous operational satellites which measure at only one or two fixed local times, for the duration of their missions. In these cases, the zonal mean trends derived from various satellite data are tied to the specific local times at which each instrument samples the data, and the trends are then also biased by the local time. Consequently, care is needed in comparing trends based on various measurements with each other, unless the data are all measured at the same local time. Similar caution is needed when comparing with models, since the zonal means from 3D models reflect averages over both longitude and the 24 h of local time. Consideration is also needed in merging data from various sources to produce generic, continuous, longer-term records. Diurnal variations of temperature themselves, in the form of thermal tides, are well known and are due to absorption of solar radiation. We find that at least part of the reason that temperature trends are different for different local times is that the amplitudes and phases of the tides themselves follow trends over the same time span of the data. Many of the past efforts have focused on the temperature values with local time when merging data from various sources and on the effect of unintended satellite orbital drifts, which result in drifting local times at which the temperatures are measured. However, the effect of local time on trends has not been well researched. We also derive estimates of trends by simulating the drift of local time due to drifting orbits. Our comparisons with results found by others (Advanced Microwave Sounding Unit, AMSU; lidar) are favorable and informative. They may explain, at least in part, the bridge between results based on daytime AMSU data and nighttime lidar measurements. However, these examples do not form a pattern, and more comparisons and study are needed.

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Latitudinal and Local Time Variation of Ionospheric Turbulence Parameters during the Conjugate Point Equatorial Experiment in Brazil

International Journal of Geophysics ◽

10.1155/2012/103963 ◽

2012 ◽

Vol 2012 ◽

pp. 1-16 ◽

Cited By ~ 21

Author(s):

Charles S. Carrano ◽

Cesar E. Valladares ◽

Keith M. Groves

Keyword(s):

Spectral Index ◽

Local Time ◽

Conjugate Point ◽

Local Times ◽

Turbulent Intensity ◽

Scintillation Index ◽

Equatorial Anomaly ◽

Noise Measurements ◽

Gps Scintillations ◽

Turbulence Parameters

Previous authors have reported on the morphology of GPS scintillations and irregularity zonal drift during the 2002 Conjugate Point Equatorial Experiment (COPEX) in Brazil. In this paper, we characterize the turbulent ionospheric medium that produced these scintillations. Using 10 Hz GPS carrier-to-noise measurements at Boa Vista (2.9°N, 60.7°W), Alta Floresta (9.9°S, 56.1°W), and Campo Grande (20.5°S, 54.7°W), we report on the variation of turbulent intensity, phase spectral index, and irregularity zonal drift as a function of latitude and local time for the evening of 1-2 November 2002. The method of analysis is new and, unlike analytical theories of scintillation based on the Born or Rytov approximations, it is valid when the scintillation index saturates due to multiple-scatter effects. Our principal findings are that (1) the strength of turbulence tended to be largest near the crests of the equatorial anomaly and at early postsunset local times, (2) the turbulent intensity was generally stronger and lasted two hours longer at Campo Grande than at Boa Vista, (3) the phase spectral index was similar at the three stations but increased from 2.5 to 4.5 with local time, and (4) our estimates of zonal irregularity drift are consistent with those provided by the spaced-receiver technique.

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Collision Local Times and Measure-Valued Processes

Canadian Journal of Mathematics ◽

10.4153/cjm-1991-050-6 ◽

1991 ◽

Vol 43 (5) ◽

pp. 897-938 ◽

Cited By ~ 19

Author(s):

Martin T. Barlow ◽

Steven N. Evans ◽

Edwin A. Perkins

Keyword(s):

Local Time ◽

Forthcoming Paper ◽

Local Times ◽

Independent Interest ◽

Positive Probability ◽

Point Interactions ◽

Random Measures ◽

Brownian Motions ◽

Collision Local Time ◽

Finite Measures

AbstractWe consider two independent Dawson-Watanabe super-Brownian motions, Y1 and Y2. These processes are diffusions taking values in the space of finite measures on ℝd. We show that if d ≤ 5 then with positive probability there exist times t such that the closed supports of intersect; whereas if d > 5 then no such intersections occur. For the case d ≤ 5, we construct a continuous, non-decreasing measure–valued process L(Y1, Y2), the collision local time, such that the measure defined by , is concentrated on the set of times and places at which intersections occur. We give a Tanaka-like semimartingale decomposition of L(Y1, Y2). We also extend these results to a certain class of coupled measurevalued processes. This extension will be important in a forthcoming paper where we use the tools developed here to construct coupled pairs of measure-valued diffusions with point interactions. In the course of our proofs we obtain smoothness results for the random measures that are uniform in t. These theorems use a nonstandard description of Yi and are of independent interest.

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