Mean Solar Time Research Articles

The simplest method for the accurate determination of noon

In this paper, we present the simplest possible method for the precise determination of solar noon in mean solar time, based only on the value of the equation of time corresponding to a predetermined time for the observer, constant throughout the year. This represents a revolutionary simplification of the appendix of the universally known SPA (Solar Position Algorithm, NREL) regarding solar noon. Given that the proposed simple method does not entail a significant loss of precision, it is especially useful for university students or postgraduate students in photovoltaic/solar thermal energy or developers who wish to quickly calculate solar noon or create their own software for analysis or research. In addition, an interpolative procedure is presented to further enhance the precision of the method, although such improvement will not be necessary in the majority of cases.

WHERE WAS MEAN SOLAR TIME FIRST ADOPTED?

It is usually stated in the literature that Geneva was the first city to adopt mean solar time, in 1780, followed by London (or the whole of England) in 1792, Berlin in 1810 and Paris in 1816. In this short paper I will partially revise this statement, using primary references when available, and provide dates for a few other European cities. Although no exact date was found for the first public use of mean time, the primacy seems to belong to England, followed by Geneva in 1778-1779 (for horologists), Berlin in 1810, Geneva in 1821 (for public clocks), Vienna in 1823, Paris in 1826, Rome in 1847, Turin in 1849, and Milan, Bologna and Florence in 1860.

Wind retrieval from temperature measurements from the Rover Environmental Monitoring Station/Mars Science Laboratory

This work presents a novel method for the real-time retrieval of wind speed on the surface of Mars that uses temperature measurements from the Rover Environmental Monitoring Station (REMS) instrument onboard the Curiosity rover of the Mars Science Laboratory (MSL) mission. After final failure of the Wind Sensor (WS) in sol 1491, REMS has not been providing wind data. The new wind retrieval approach that we propose may eventually be able to supply MSL with wind values for contextualizing the rover’s operations and for meteorological studies on the surface of Mars. The new method is based on forced convection modeling of the Air Temperature Sensors (ATS) of REMS as thin rods immersed in the extreme low-pressure and high-radiating atmospheric conditions of the Martian thermal boundary layer at a height of ∼1.5 m from the surface. A preliminary validation of the possibilities and limitations of this retrieval has been performed using comparative analysis with existing REMS wind field-site data for the same sols that are available at the Planetary Data System (PDS). We have developed both a “coarse” approach, in which wind speed is determined with no regard to wind direction, and a “refined” method, in which it is attempted to determine both wind speed and direction. Assuming the previously reported WS retrieval errors of 20% for the wind speed, we report an agreement to the WS values of wind speed ranging from 36.4% to 77% of the acquisition time for the “coarse” approach, depending on the sol examined. These promising results are limited to only evening extended acquisitions from 18:00 to 21:00 local mean solar time (LMST). This method could be applied to daytime conditions. The results suggest a new optimal orientation for wind speed retrieval of +60°clockwise with respect to the forward direction of the Curiosity rover, although the technique is not yet ready to be considered for planning of the Curiosity rover operations. This method could extend the wind characterization of the Gale Crater for future Curiosity rover data acquisitions by recycling air temperature measurements and provide the scientific community with a data set for future comparative analysis with the Temperature and Wind Sensors for InSight (TWINS)/InSight, the HabitAbility: Brines, Irradiation and Temperature (HABIT)/ExoMars 2022, and the Mars Environmental Dynamics Analyzer (MEDA)/Mars 2020 rover instruments.

Кутові характеристики розсіювання сонячного світла земною атмосферою, спостережувані приладом «ScanPol» проєкту «АEROSOL-UА»

Angular characteristics of solar light scattering in the Earth’s atmosphere and parameters of the atmosphere volume and the surface part observed by the ScanPol instrument of the “Aerosol-UA” project are estimated in order to determine properties of aerosol particles from a satellite orbit. Estimations were obtained for the scattering angles ranges in the lower troposphere which can be observed by the ScanPol instrument from the polar sun-synchronous orbit with altitude 705 km and inclination 98.1° crossing the ascending knot on the equator at 21h 30m, 22h 30m, and 23h 30m of local mean solar time. The estimations of the scattering angles were obtained at each of the orbit realizations for sites on the Earth’s surface, were the zenith angle of the Sun is 80°, 50°, and minimal one for each of the orbit realizations. The calculations were performed for the dates of 2020 close to the summer solstice, the autumnal equinox, and the winter solstice (namely 21 June, 21 September, and 21 December, respectively). The scattering angles range was computed for the range of the ScanPol scanning angles equal to 110° along the sub-satellite trace. The range of scattering angles is maximal at the considered here maximal zenith angle of the Sun equal to 80°, which occurs in the polar latitudes of the northern hemisphere during the period between the spring and the autumnal equinoxes and in the middle latitudes during the rest of a year. The maximal range of scattering angles is approximately 51.1°...149.5° close to the summer solstice for the satellite orbit with local time of crossing the ascending knot (TBB) equal to 21h 30m and 41.9°...172.9° for the orbit with ТВВ = 23h 30m. The minimal range of scattering angles occurs at minimal zenith angles of the Sun close to the winter solstice and takes on the values approximately 103.2°...142.8° and 108.2°...170.4° at mentioned ТВВ, respectively. For the rest of the zenith angles of the Sun, the range of scattering angles takes on the intermediate values. The range of scattering angles decreased mainly at the cost of small scattering angles. In summary, the range of observed scattering angles is maximal for the orbit with local time close to the noon, to be precise at TBB between 22h 30m and 24h 00m for the orbit with inclination assumed here. Comparison of the ranges of scattering angles observed by the ScanPol instrument and data of simulations showed that measurements by ScanPol from the considered orbit allow us to retrieve microphysical and optical properties of aerosol particles. Linear size of the scene observed by instrument along the sub-satellite trace increases during the scanning process from approximately 6 km at nadir to almost 60 km at maximal scattering angle equal to 60°, and simultaneously the longitude of the observed scene decreases by 1.55° that corresponds to linear shift along the parallel from DS »172 km on the equator to DS » 24.5 km on the latitude 82°. That is why data measured by the ScanPol can be used after mesoscale averaging.

A note on apparent solar time and the seasonal cycle of atmospheric solar tides

Both observations and comprehensive model simulation data of atmospheric fields are generally available at fixed Mean Solar Times through the day, which is convenient as the notional ‘mean sun’ progresses around the Earth each day in exactly 24 h. This article reports on a simple investigation of the effect of correcting data taken in Mean Solar Time to account for the difference in position between the actual (or ‘apparent’) sun and the mean sun, with a focus on characterizing atmospheric tidal oscillations. In particular, we found that the annual cycle in the phase of the semidiurnal atmospheric tidal oscillation of surface pressure near the Equator is almost entirely explained by the difference between Mean Solar Time and Apparent Solar Time. This result was confirmed in raw barometric observations as well as in several global reanalysis datasets.

Analysis of wind-induced dynamic pressure fluctuations during one and a half Martian years at Gale Crater

The Rover Environmental Monitoring Station (REMS) instrument on-board the Mars Science Laboratory (MSL) has acquired unprecedented measurements of key environmental variables at the base of Gale Crater. The pressure measured by REMS shows modulations with a very structured pattern of short-time scale (of the order of seconds to several minutes) mild fluctuations (typically up to 0.2 Pa at daytime and 1 Pa at night-time). These dynamic pressure oscillations are consistent with wind, air and ground temperature modulations measured simultaneously by REMS. We detect the signals of a repetitive pattern of upslope/downslope winds, with maximal speeds of about 21 m/s, associated with thermal changes in the air and surface temperatures, that are initiated after sunset and finish with sunrise proving that Gale, a 4.5 km deep impact crater, is an active Aeolian environment. At nighttime topographic slope winds are intense with maximal activity from 17:00 through 23:00 Local Mean Solar Time, and simultaneous changes of surface temperature are detected. During the day, the wind modulations are related to convection of the planetary boundary layer, winds are softer with maximum wind speed of about 14 m/s. The ground temperature is modulated by the forced convection of winds, with amplitudes between 0.2 K and 0.5 K, and the air temperatures fluctuate with amplitudes of about 2 K. The analysis of more than one and a half Martian years indicates the year-to-year repeatability of these environmental phenomena. The wind pattern minimizes at the beginning of the south hemisphere winter (Ls 90) season and maximizes during late spring and early summer (Ls 270). The procedure that we present here is a useful tool to investigate in a semi-quantitative way the winds by: i) filling both seasonal and diurnal gaps where wind measurements do not exist, ii) providing an alternative way for comparisons through different measuring principia and, iii) filling the gap of observation of short-time wind variability, where the REMS wind sensor is blind.

Changes of solar magnetic asymmetry

The results of an analysis of the north–south asymmetry in solar activity and solar magnetic fields are reported. The analysis is based on solar mean magnetic field and solar polar magnetic field time series, 1975–2015 (http://wso.stanford.edu), and the Greenwich sunspot data, 1875–2015 (http://solarscience.msfc.nasa.gov/greenwch.shtml). A long-term cycle (small-scale magnetic fields, toroidal component) of ~140 years is identified in the north–south asymmetry in solar activity by analyzing the cumulative sum of the time series for the north–south asymmetry in the area of sunspots. A comparative analysis of the variations in the cumulative sums of the time series composed of the daily values of the sun’s global magnetic field and in the asymmetry of the daily sunspot data over the time interval 1975–2015 shows that the photospheric large-scale magnetic fields may also have a similar long-term cycle. The variations in the asymmetry of large-scale and small-scale solar magnetic fields (sunspot area) are in sync until 2005.5 and in antiphase since then.

‘the most perfect instrument’: Reassessing Sundials in Romantic Literature

Discussions of temporality in Romantic literature generally distinguish between objective forms of time-telling (clock time) and subjective varieties (psychological time). Although critics have tended to neglect the former, perceiving it to be ‘boringly numerical’ and the ‘lowest’ form of horology, the present article examines the complexities of practical time-telling from a broadly ecocritical perspective, arguing that, far from being a tedious embodiment of cold systematic regularity, the maddening untrustworthiness of clocks and watches ensured that time-telling was an unavoidably relativistic activity which caused frequent frustration, anxiety, and confusion throughout the period. By the late eighteenth century, apparent solar time (so-called ‘sundial time’) was gradually being superseded by mean solar time, and, even though the latter potentially offered greater regularity, the calculation of the mean itself varied depending upon the meridian used. Greenwich Mean Time, determined from the prime meridian in Greenwich, was adopted by the Railway Clearing House in 1847, eventually becoming the standard time zone for Great Britain in 1880, and a world standard in 1884. However, during the period 1780 to 1830, these distinct systems were all in common use simultaneously, and the periodicals’ letters pages regularly contained proposals for a unified system. In 1829, J. Utting prophesied that ‘the time is not far distant when mean solar time will be adopted, in nautical astronomy in particular, to the complete exclusion of apparent time’. Paul Glennie and Nigel Thrift have recently examined how these various systems were deployed, and they have boldly concluded that ‘[. . . ] there is no such thing as clock time. Rather clock time comprises a number of concepts, devices, and practices which have meant different things at different times and places, and even in any one place have not had a unitary meaning’. So far, sundials have not featured prominently in such reappraisals, yet, as time-telling devices, they fuse ecological and horological concerns in a distinctive manner. Since the early 1990s, ecocriticism has repeatedly sought to ‘collapse the artificial distinctions between nature and culture’, and Ashton Nichols has recently destabilised this dichotomy even further by focusing on ‘urbaniture’, a domain in which the natural and the urban are ‘linked in a complex web of interdependent interrelatedness’. Sundials do not impose upon or coerce nature; rather, they inertly display the diurnal regularities that are manifest as the earth spins on its axis while orbiting the sun. By contrast, mechanical timepieces tried to be consistent with the

Solar time, legal time, time in use

The International Conference held in 1884 at Washington defined a universal time as the mean solar time at the Greenwich meridian (GMT). Now, the Universal Time, version UT1, is strictly defined as proportional to the angle of rotation of the Earth in space. In this evolution, the departure of UT1 from GMT does not exceed one or two seconds. This is quite negligible when compared with the departure between the solar time and the legal time of citizens, which may exceed two hours without raising protests.

Earth rotation monitoring, UT1 determination and prediction

Monitoring the Earth's rotation angle is essential in various domains linked to reference systems such as space navigation, precise orbit determinations of artificial Earth satellites including the Global Navigation Satellite Systems (GNSS), positional astronomy and for geophysical studies on time scales ranging from a few hours to decades.Universal Time UT1 is based on the rotation of the Earth on its axis. Historically it was related to mean solar time on the meridian of Greenwich, sometimes known as Greenwich Mean Time. Monitoring Earth orientation, and in particular UT1, is the primary task of the International Earth Rotation and Reference Systems Service (IERS). The Earth Orientation Center is responsible for monitoring Earth orientation parameters (EOPs) including long-term consistency and leap second announcements. The Rapid Service/Prediction Center is in charge of the rapid, near real-time solution and predictions. These two complementary services of the IERS provide Earth orientation information from results derived predominantly from Very Long Baseline Interferometry with valuable input from GNSS observations and global atmospheric angular momentum for both the combination and prediction of EOPs.

Free core nutation: direct observations and resonance effects

The motion of Earth's spin axis in space is monitored by Very Long-Baseline Interferometry (VLBI), and since 1994 also its rate is measured by Global Positioning System (GPS). The method of “combined smoothing”, developed recently at the Astronomical Institute in Prague enables one to combine both series. The solution, based on observations in 1979.6–2004.7, is compared with the recently adopted IAU2000 model of precession-nutation. The analysis reveals substantial residual offsets from the model. The dominant peak in frequency domain can be identified with Retrograde Free Core Nutation (RFCN), and we find also statistically significant deviations of several forced nutation terms. From the direct analysis of VLBI observations of celestial pole offsets from IAU2000 model of precession-nutation, it follows that the dominant period apparently grew from the average 435 days (VLBI observations in 1983.7–2004.7) to 460 days (VLBI/GPS combination in 1994.3–2004.6). A study of indirect determination of the RFCN period from the observed forced nutation terms through the resonance effects is presented, and the difference from the value found by direct analysis is discussed. It is demonstrated that the resonance approach does not confirm the apparent change of the period obtained from the direct analysis of observed celestial pole offsets; the resonance value is close to 430 solar days, and it seems to be very stable in time. The different value found from the direct analysis of observations can be probably ascribed to a small additional excitation by the atmosphere and/or ocean with retrograde terrestrial period around 23h 53min mean solar time.

The Mars Reconnaissance Orbiter Mission

The Mars Reconnaissance Orbiter (MRO) will be launched in August 2005 by an Atlas V 401 expendable launch vehicle from Cape Canaveral Air Force Station, USA. It will deliver to Mars orbit a payload to conduct remote sensing science observations, identify and characterize sites for future landers, and provide critical telecom/navigation relay capability for follow-on missions. The mission is designed to provide global, regional survey, and targeted observations from a low 255 km by 320 km Mars orbit with a 3:00 PM local mean solar time (ascending node). During the one Martian year (687 Earth days) primary science phase, the orbiter will acquire visual and near-infrared high-resolution images of the planet's surface, monitor atmospheric weather and climate, and search the upper crust for evidence of water. After this science phase is completed, the orbiter will provide telecommunications support for spacecraft launched to Mars in the 2007 and 2009 opportunities. The primary mission ends on December 31, 2010, approximately 5.5 years after launch.

Taking advantage of inclination variation in resonant remote-sensing satellite orbits

The inclination of remote-sensing satellites, which are generally placed in sun-synchronous orbits, varies as a function of the nominal equatorial crossing local mean solar time selected for a given mission. The Indian Remote-Sensing satellites will have an inclination reduction of about 0.034° per year and for most of the satellites, the local time chosen was around 10:30 hours at descending node. In practice, the initial inclination is biased appropriately so that the expensive out-of-plane maneuvers could be taken up after few years of mission operations, depending on the deviations permitted in the local time for a given mission. However, the scenario differs when the mission objectives require an almost exact repeat orbit of 14 or 15 per day. In such a situation, the satellite orbit, which passes through a 14th or 15th order resonance, undergoes a nearly secular increase in orbit inclination. This paper presents a detailed analysis carried out for such an orbit, based on Cowell's approach. Long-term predictions have been carried out by considering all major forces that perturbs the satellite orbit. Observed behavior of orbit, based on the daily definitive orbit determination is also presented. The variation in inclination and the cause is clearly brought out. Further, it is demonstrated that the selection of longitude for nominal ground track pattern has an impact on the inclination variation. A proposal is made to take advantage of such expected inclination variation so that initial inclination bias can be chosen appropriately. Ground track longitude can be chosen to take advantage, subject to the mission coverage requirements. The paper contains the results of an exhaustive analysis of the actually observed orbit resonance. It is felt that the work has both theoretical and operational importance for remote-sensing missions.

The Measurement of Time: Time, Frequency and the Atomic Clock

This book provides an in-depth and comprehensive survey of the current state-of-the-art of the international atomic timescale and its underpinning relationship to practical and legal timescales. The authors are two of the leading figures in French time metrology. Claude Audoin, formerly Director of the Laboratoire de l'Horloge Atomique at Orsay, has had a long and distinguished career in the development of atomic frequency standards and atomic clocks. Bernard Guinot, formerly Director of the Bureau International de l'Heure (now absorbed by the Bureau International des Poids et Mesures, BIPM), has a lifetime's experience in the development of timescales. The work reviewed here is a revised and updated translation of Les fondaments de la mesure du temps (Paris: Masson, 1998). It is written at a level appropriate for an experienced graduate student or postdoctoral scientist entering either the field of time and frequency metrology or that of precise astronomical observation, whilst having sufficient depth to be useful as a work of reference for the established researcher in these fields. The first third of the book discusses the physical foundations of time metrology and introduces key concepts in the use of physical oscillators as clocks. The historical account of the complex process by which mean solar time came to be replaced by Coordinated Universal Time (UTC) will be particularly informative for newcomers to the field. About half of the volume is devoted to atomic frequency standards, with an exposition of the physics of caesium beam clocks and caesium fountains and a review of other commonly used standards such as the hydrogen maser, rubidium cell and stored ion clock. Although thorough, this 127-page chapter does not replace Audoin's earlier work with Jacques Vanier, The Quantum Physics of Atomic Frequency Standards (Bristol: IOP Publishing, 1989, out of print), which will remain the Bible for physicists working on clock development. The present time is one of great excitement in the development of atomic frequency standards. At the time the French edition was published, the first caesium fountain frequency standard, at the BNM-LPTF in Paris, had recently demonstrated 1.5 × 10-15 relative frequency uncertainty. Two such standards, at PTB and NIST, are now contributing to International Atomic Time (TAI). Clocks based on optical transitions in ions or atoms are just beginning to become a reality, thanks to Ted Haensch's breakthrough with the femtosecond optical frequency comb generator, which arrived on the scene just in time to receive a mention in this English edition. In a rapidly evolving field, any general survey is bound to be overtaken by events. Primary caesium frequency standards are designed to realize the SI definition of the second. The relationships between the SI second, TAI and UTC, as well as the national approximations to UTC generated by national standards laboratories such as NPL, the timescale available from GPS and timescales used in astronomy, are carefully set out. Finally, the practical applications of these timescales and frequency standards are reviewed, ranging from ultraprecise determinations of fundamental physical constants to positioning and navigation. The problem of longitude is as pressing as in Harrison's day, but for the foreseeable future, clockmakers will continue to have the upper hand over astronomers! Despite betraying the occasional Gallicism, the English translation reads with the clarity of the French original. The reader is guided painlessly through the multiplicity of acronyms with which the topic abounds. Audoin and Guinot have produced a book that will stand the test of time. Stephen N Lea

A unified and general treatment of solar calendars and sundials

The equations of the most general type of solar calendar and sundialare derived from fundamental principles, in a manner that requires onlyelementary geometry and trigonometry. True solar time and mean solar time areboth taken into consideration. The results are suitable for usein students' projects, for instance of the type described by Kibble(1999 Phys. Educ. 34 130).

A post-Pathfinder evaluation of areocentric solar coordinates with improved timing recipes for Mars seasonal/diurnal climate studies

The accurate determination of the Mars pole vector derived from Pathfinder and Viking Lander radio data ( Folkner et al., 1997. Science 278, 1749–1752), together with the VSOP87 representation of planetary orbits (Bretagnon and Francou, 1988. Astron. Astrophys. 202, 209–315), have been applied to a new evaluation of the right ascension of the “Fictitious Mean Sun” (FMS) at Mars. With Δ t J2000 the elapsed time in days from the J2000 epoch (JD 2451545.0 TT), α FMS=270°.3863+0.5240384(°/d)·Δ t J2000−4×10 −13(°/d 2)·Δ t 2 J2000 represents a best least-squares quadratic fit of the FMS, including aberration, to each instance of the four equinox and solstice passages for each of 134 Mars orbits spanning the calendar years 1874–2126. The implied tropical orbit period for Mars, 686.9726 d, closely agrees with the recent evaluations by Surán (1997. Planet. Space Sci. 45, 705–708) and Allison (1997. Geophys. Rev. Lett. 24, 1967–1970). Together with the Pathfinder radio determination of the Mars sidereal rotation, the derived FMS rate corresponds to a mean solar day (or “sol”) of 1.02749125 d. The new FMS determination would serve to define the Mean Solar Time at Mars to the nearest tenth-second, according to historical conventions originally established for terrestrial time-keeping, once the Mars prime meridian defined by the crater Airy-0 is determined within inertial space to the same accuracy. For convenient reference to current epochs, 2000 January 06 00:00:00 UTC (=MJD 51549.000 UTC) corresponds to a coincidence of α FMS and the rotation angle of the crater Airy-0 measured with respect to the Mars equinox (i.e. “mean solar midnight” on the planet’s prime meridian), to within the current uncertainty in the locational definition of the planet’s cartographic grid. As a further result of the analysis, the consistently derived Mars obliquity of date is ϵ=25°.192+3.45×10 −7(°/d)·Δ t J2000. An improved analytic recipe for the calculation of the solar areocentric longitude ( L S) of Mars to an accuracy better than 0°.01 is also provided, accounting for the primary perturbations of Earth, Jupiter, and Venus, which may in turn be applied to an efficient evaluation of Mars Local True Solar Time (LTST) to within the uncertainty of the inertial position of the Mars prime meridian. For specific applications to the data archives for landed Mars spacecraft, simple conversion formulae are given for the determination of the Viking “Local Lander Time” and the Pathfinder “Local True Solar Time” in terms of the terrestrial calendar date and UTC.

Observation of terrestrial orbital motion using the cosmic-ray Compton–Getting effect

Using underground observations, we have found a small diurnal amplitude modulation of the cosmic-ray muon intensity which agrees in amplitude and phase with a first-order relativistic effect due to the Earth's motion, as discussed by Compton and Getting more than fifty years ago. The parent particles are sufficiently rigid (∼1.5TeV/c) that solar and geomagnetic effects should be minor. The muon flux deep underground is relatively insensitive to near-surface meteorological effects, and temperature effects at production height would produce intensity variations nearly out of phase with the observed effect. Analysis of the arrival times of 5 × 108 muons during a period of 5.4 yr yields a fractional amplitude variation of 2.5+0.7−0.6× 10−4, with a maximum near dawn, at 08:18 ± 1.0 h local mean solar time (LT). The expected amplitude is 3.40 × 10−4, with the maximum at 06:00 LT.

Oscillation of High-Level Cirrus and Heavy Precipitation around Australian Region Tropical Cyclones

Abstract A study of 27 days of three-hourly GMS infrared data for 11 tropical cyclones in the Australian region has revealed that the area of the cirrus canopy executes a marked diurnal oscillation with maximum at +3 h of 0800 LMST Mean Solar Time (LMST) and minimum at ±3 h of 1800 LMST. In the mean, the ratio of maximum to minimum area is 1.7:1. This diurnal oscillation is 12 h out of phase with that in the North Atlantic. A weaker daytime oscillation also exists on most days with minimum and maximum areas occurring most frequently at ±3 h of 0900 and 1200 LMST, respectively. Heavy precipitation associated with tropical cyclones, measured on the only atoll in the Southwest Pacific with long rainfall records, has almost the same bi-modal oscillation as that of the area of the cirrus canopy. There is some evidence that during and immediately after a stage of cyclone intensification the oscillation of the area of the cirrus canopy changes considerably.

Diurnal Oscillation of the Area of Cloudiness Associated with Tropical Storms

An analysis of 16 days from eight Atlantic storms, two in 1974 and six in 1975, objectively quantified a suspected diurnal oscillation of tropical storm cirrus cloud cover. The oscillation shows a maximum area at approximately 1700 local mean solar time and a minimum area at 0300 local mean solar time. The average ratio of the maximum area to the minimum area is 1.65. SMS infrared imagery was analyzed with a scanning false-color densitometer to obtain area measurements of the cloudiness associated with the storms. These measurements were made approximately every 1½ h at three temperature thresholds: 253, 239 and 223 K. Two tests were performed to rule out the possibility of the oscillation being due either to the satellite sensor or to image processing. Measurement of the ocean surface temperature, was made with SMS-I to determine whether the sensor detected a constant ocean temperature. The second test compared simultaneous area measurements obtained by SMS-I and SMS-II. The results of these tests support the storm oscillation detected. Two other related phenomena were also observed: 1) the amplitude of the area oscillation is apparently inversely proportional to the intensity of the storm, and 2) a time-dependent, shorter period oscillation is superimposed on the daily oscillation. Inferences of causality are made.

On the problem of lunar time

New achievements in lunar investigations by spacecrafts provide the reasons why some new international scale of special lunar time nowdays is under discussion. However, the introduction of special time scales for other celestial bodies would turn to be a complex affair. To document this point of view it is shown that, both for making precise astrometrical calculations and for creating a lunar calendar, it should be reasonable to make use of the generally accepted scales of terrestrial time; there is no real need to introduce any special lunar time unit. For calendar needs it is suggested to introduce a local scale of time based on count of the lunations and usual mean solar time units being used within the every lunation.