A simple empirical method of asteroid proper elements calculation is proposed. The method uses distributions of osculating orbital elements, such as longitude of ascending node, inclination and ...longitude of perihelion, and eccentricity. These distributions make it possible to obtain forced elements. The forced elements define long-periodic variations of osculating elements. The proper elements are calculated by elimination of the short- and long-periodic perturbations from the osculating ones. In this paper, the short-period perturbations were removed by means of numerical integration, whereas the removal of long-periodic terms was done by using the coordinate transformation formula. The derived proper elements are accurate enough to search for asteroid families. The method is effective in both non-resonant and resonant cases. As an example, the asteroids in 3:2 and 1:1 mean-motion resonances with Jupiter were investigated. The proper elements were calculated for all multi-opposition asteroids in these zones. Due to the large number of the asteroids real families are clearly apparent in distributions of the proper elements. An approach similar to the hierarchical clustering method was used for identification of the families. Using this technique, two robust asteroid families of (1911) Schubart and (153) Hilda were identified in the Hilda-group. And four families were found among L4-trojans: (3548) Eurybates, (2148) Epeios, (624) Hektor, and (9799) 1996RJ. The taxonomy of these families was analysed. The most tight and populated families consist of C and X asteroids, while the D-type asteroids predominate in the background population. No reliable families have been identified near the libration point L5.
In this paper, the Lidov–Kozai mechanism was studied in the region of the Hilda group and Jupiter Trojans. Asteroids of these populations move in 3:2 and 1:1 orbital resonances with Jupiter. The ...study was carried out using numerical integration of real asteroids’ equations of motion. A simplified dynamical model was adopted. Perturbations from only Jupiter moving in a fixed elliptical orbit were taken into account. Classical secular perturbations were excluded from osculating elements at every print step, and derived orbital inclinations and eccentricities were plotted versus a perihelion argument
ω
. As a result, it was found that usual positions of a maximum of the eccentricity and, accordingly, a minimum of the inclination (
ω
=
90
∘
,
270
∘
) are shifted in these resonant regions. For Hildas, the maximum of the eccentricity is achieved with perihelion argument values
ω
=
0
∘
,
180
∘
. For L4 Trojans, it is achieved with
ω
=
30
∘
,
210
∘
, and for L5 Trojans—with
ω
=
150
∘
,
330
∘
.
Abstract
A search for asteroid families was carried out with the use of a proper element set comprising 649 050 asteroid orbits. Proper elements were calculated by the empirical method. This method ...uses distributions of orbital elements to calculate secular perturbations. There are two types of secular perturbations: the classical perturbations and the Lidov–Kozai mechanism. The empirical method allows us to distinguish these perturbations in distributions of orbital elements. In this work, amplitudes of inclination and eccentricity oscillations were calculated for both types of perturbations, and thereafter the perturbations were excluded from the osculating elements one after another. The exclusion was made by means of the coordinate transformation formula. The method can be applied for high-inclination and resonant regions. The obtained proper elements are accurate enough to search for asteroid families. As a result, 141 asteroid families were identified in the interval of a semimajor axis 1.8–5.4 au.
A data‐constrained ocean state estimate that permits closed property budget diagnostics is used to examine the balance between surface forcing (
F¯), advective (
A¯), and diffusive (
D¯) fluxes in ...maintaining the large‐scale time‐mean surface salinity
Ss¯. Time‐mean budgets (1993–2010) are considered for the 10 m thick top layer. In general,
D¯ tends to counteract
F¯, but
A¯ is important almost everywhere, and some regions show a main balance between
A¯ and
D¯ (Bay of Bengal, Arctic) or
A¯ and
F¯ (tropical Atlantic and Pacific). Advection tends to freshen the surface in the tropics and high latitudes, with opposite tendencies in midlatitudes. For various
Ss¯ tropical extrema,
A¯ adds to the
F¯ tendencies in precipitation regions and opposes
F¯ in evaporation regions. Long‐term
Ss¯ conditions thus reflect more than a simple diffusive adjustment to
F¯, likely involving close interaction between wind‐ and buoyancy‐driven circulation and mixing processes.
Key Points
A global ocean state estimate yields closed budget diagnostics of the mean surface salinity balance
Surface advection plays a key role in balancing forcing and diffusion tendencies in most regions
Advection tends to freshen the tropics and high latitudes and add salt to midlatitudes
Multifunctional activity of the
PDX1
gene product is reviewed. The PDX1 protein is unique in that being expressed exclusively in the pancreas it exhibits various functional activities in this organ ...both during embryonic development and during induction and progression of pancreatic cancer. Hence, PDX1 belongs to the family of master regulators with multiple and often antagonistic functions.
The relation between large‐scale sea level and bottom pressure variability is studied using long (50‐yr) simulations of a general circulation model under realistic forcing. Admittance and coherence ...analyses are used to characterize the bottom pressure and sea level relationship as a function of period, horizontal spatial scale, and location. At the model grid scale (1°), bottom pressure is found to be essentially equivalent to sea level at periods <30 days, except in the tropics. This equivalence still holds for longer periods (∼100 days), but only at high latitudes (>60°) and in shallow depths (<200 m). Elsewhere, bottom pressure and sea level fields can differ significantly. Results indicate an increase of the importance of baroclinic signals with decreasing latitude and spatial scale, with significant baroclinic signals at intra‐seasonal and longer periods present in many subtropical and mid‐latitude regions. Variability is clearly baroclinic at inter‐annual periods, regardless of location and spatial scale. Results have broad implications for the interpretation and processing of both satellite altimetry and gravity data and for their assimilation into numerical models.
The annual exchange of water between the continents and oceans is observed by GPS, gravimetry, and altimetry. However, the global average amplitude of this annual cycle (observed amplitude of ∼8 mm) ...is not representative of the effects that would be observed at individual tide gauges or at ocean bottom pressure recorders because of self‐attraction and loading effects (SAL). In this paper, we examine the spatial variation of sea level change caused by the three main components that load the Earth and contribute to the water cycle: hydrology (including snow), the atmosphere, and the dynamic ocean. The SAL effects cause annual amplitudes at tide gauges (modeled here with a global average of ∼9 mm) to vary from less than 2 mm to more than 18 mm. We find a variance reduction (global average of 3 to 4%) after removing the modeled time series from a global set of tide gauges. We conclude that SAL effects are significant in places (e.g., the south central Pacific and coastal regions in Southeast Asia and west central Africa) and should be considered when interpreting these data sets and using them to constrain ocean circulation models.
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