Pair Of Satellites Research Articles

Astrometry from CCD photometry of mutual events of Jovian satellites from VBO during 1997

Astrometric results of CCD observations of the mutual events of the Galilean satellites of Jupiter from the Vainu Bappu Observatory are presented. The shifts in the photo-centers on the disks of Io and Europa due to albedo variations inferred from the available mosaics of Galileo imagery are determined. The estimated shifts from ≈ 90 km East to ≈ 50 km West on Io and from ≈ 50 km East to ≈ 30 km West for Europa during one orbital period are comparable to the accuracies provided by the present-day ephemerides. In a given mutual event series, the mutual events involving a given satellite pair dominate in number and occur nearly at the same orbital longitude within ± ; all the events are therefore delayed or all of them advanced depending on the direction of the shift of the photo-center. The implications of including these cumulative and sustained longitude residuals on the constructed ephemerides are discussed.

Implications from Galileo Observations on the Interior Structure and Chemistry of the Galilean Satellites

Data from the recent gravity measurements by the Galileo mission are used to construct wide ranges of interior structure and composition models for the Galilean satellites of Jupiter. These models show that mantle densities of Io and Europa are consistent with an olivine-dominated mineralogy with the ratios of Mg to Fe components depending on mantle temperature for Io and on ice shell thickness for Europa. The mantle density and composition depend relatively little on core composition. The size of the core is largely determined by the core's composition with core radius increasing with the concentration of a light component such as sulfur. For Io, the range of possible core sizes is between 38 and 53% of the satellite's radius. For Europa, there is also a substantial effect of the thickness of the ice layer which is varied between 120 and 170 km on the core size. Core sizes are between 10 and 45% of Europa's radius. The core size of Ganymede ranges between one-quarter and one-third of the surface radius depending on its sulfur content and the thickness of the ice shell. A subset of the Ganymede models is consistent with an olivine-dominated mantle mineralogy. The thickness of the silicate mantle above the core varies between 900 and 1100 km. The outermost ice shell is about 900 km in thickness and is further subdivided by pressure-induced phase transitions into ice I, ice III, ice V, and ice VI layers. Callisto should be differentiated, albeit incompletely. It is proposed that this satellite was never molten at a large scale but differentiated through the convective gradual unmixing of the ice and the metal/rock component. Bulk iron-to-silicon ratios Fe/Si calculated for the inner pair of satellites, Io and Europa, are less than the CI carbonaceous chondrite value of 1.7±0.1, whereas ratios for the outer pair, Ganymede and Callisto, cover a broad range above the chondritic value. Although the ratios are uncertain, in particular for Ganymede and Callisto, the values are sufficiently distinct to suggest a difference in composition between these two pairs of satellites. This may indicate a difference in iron–silicon fractionation during the formation of both classes of satellites in the protojovian nebula.

Multispacecraft measurements of plasma and magnetic field variations in the magnetosheath: Comparison with Spreiter models and motion of the structures

Large (from tens of percent up to several times) ion flux (or density) and magnetic field magnitude variations are typical magnetosheath features. Case and statistical comparisons of simultaneous solar wind observations, magnetosheath observations, and the gasdynamic model for the magnetosheath flow of Spreiter et al. (Planet. Space Sci. 14 (1966) 223) show that two types of magnetosheath plasma and magnetic field variations exist: • in some cases, they are a repetition or amplification of solar wind or IMF disturbances which pass through the bow shock; • but in the most cases, these variations are endogenous; i.e., they originate inside the magnetosheath. Persistence times and/or correlation lengths for the magnetosheath plasma variations were investigated via detailed comparison of simultaneous magnetosheath measurements from several spacecraft. For small separation distances (about 0.5 R E) we used the satellite pair INTERBALL-1/MAGION-4; for larger distances (up to 10–30 R E on the same or on the opposite flanks of the magnetosheath) we used the INTERBALL-1/GEOTAIL/IMP 8 measurements. In some cases, we observed a remarkable coincidence of the magnetosheath plasma behavior from the spacecraft separated by more than 10 R E. It seems that the compression plasma structures move tailward together with the magnetosheath plasma flow.

<i>Introduction</i> The Interball project after 6 years of data analysis

The Interball project consists of two pairs of satellites orbiting in the Earth’s magnetosphere. It was managed by the Russian space agency (RKA) in the framework of a wide international cooperation. The Interball-1 pair, comprising a main Prognoz type satellite and a subsatellite, MAGION4, was launched in August 1996 into a highly elongated (800 km perigee, 190 000 km apogee altitude), 62.8 inclined orbit which crossed the equatorial parts of the Earth’s environment at distances of a few tens of Earth’s radii, and was therefore particularly suitable for solar wind/magnetosheath and magnetospheric substorm studies. The main purpose of the subsatellites of the Interball-1 pair was to search for cause-and-effect relationships by performing measurements synchronized with those made on the main satellite. Measurements at two different points in space enable one to distinguish reliably (in one direction, at least) the locations and motions of various plasma structures and/or inhomogeneities, thus making a correct interpretation of experimental results easier.

On the use of an effective ionospheric height in electron content measurement by GPS reception

An experimental method, using simultaneous vertical and slant observations, has been derived for estimating the effective shell height for electron content measurement by GPS reception. At a latitude of approximately 53° north, Lancashire is well placed as an observing site since GPS satellite orbits are inclined at 55° to the Earth's equatorial plane and, as a result, many GPS tracks pass almost directly overhead, giving true zenithal measurements. This paper focuses on the question of oblique‐to‐zenithal correction and related matters. In particular, plasmaspheric effective height and satellite bias corrections are determined by measuring the total electron content (TEC) from pairs of satellites to a single ground station, each pair giving simultaneous observations of oblique and zenithal TEC. Additional bias corrections are determined by extracting the TEC using pairs of satellites with the same elevation at the same time. The Chapman Production Function Model and the Sheffield University Plasmasphere and Ionosphere Model are both used to determine a theoretical value for the plasmaspheric effective height. The results indicate that the plasmaspheric effective height used in the oblique‐to‐zenithal thin shell conversion is considerably greater than the commonly adopted value of 350 km. It is suggested, on the basis of all the available evidence, that a value between 600 and 1200 km is preferred. Assuming a lower value could produce an error of 15 to 30% or more in the electron content.

Dynamics of spin I=3/2 under spin-locking conditions in an ordered environment.

We have derived approximate analytic solutions to the master equation describing the evolution of the spin I=3/2 density operator in the presence of a radio-frequency (RF) field and both static and fluctuating quadrupolar interactions. Spectra resulting from Fourier transformation of the evolutions of the on-resonance spin-locked magnetization into the various coherences display two satellite pairs and, in some cases, a central line. The central line is generally trimodal, consisting of a narrow component related to a slowly relaxing mode and two broad components pertaining to two faster relaxing modes. The rates of the fast modes are sensitive to slow molecular motion. Neither the amplitude nor the width of the narrow component is affected by the magnitude of the static coupling, whereas the corresponding features of the broad components depend in a rather complicated manner on the spin-lock field strength and static quadrupolar interaction. Under certain experimental conditions, the dependencies of the amplitudes on the dynamics are seen to vanish and the relaxation rates reduce to relatively simple expressions. One of the promising emerging features is the fact that the evolutions into the selectively detected quadrupolar spin polarization order and the rank-two double-quantum coherence do not exhibit a slowly relaxing mode and are particularly sensitive to slow molecular motion. Furthermore, these coherences can only be excited in the presence of a static coupling and this makes it possible to discern nuclei in anisotropic from those in isotropic environment. The feasibility of the spin-lock pulse sequences with limited RF power and a nonvanishing average electric field gradient has been demonstrated through experiments on sodium in a dense lyotropic DNA liquid crystal.

Collisional processes and transfer of mass among the planetary satellites

Several pairs of planetary satellites may have been involved, during the history of the Solar System, in mutual mass transfer processes. Such processes can be triggered by catastrophic collisions of a satellite (parent body) with a third object. As a consequence, the collision fragments are injected into independent orbits that can cross the trajectory of the another satellite (target). These swarms of secondary impacts may be of some importance influencing the properties of the target body. Even the formation of the atmosphere around some giant satellites may have been triggered by the gas released after the impacts of fragments onto the target's surface. Moreover, the dierent albedos and the dierent surface density of impact craters within the same satellite system may be connected to peculiar collisional phenomena, such as those we are dealing with. A quantitative modelling of the role of mass transfer processes obviously requires an estimate of how much material the parent bodies are able to supply, and under what circumstances the process may take place. A general analysis of the various pairs throughout the major satellite systems present in the Solar System has been performed in the present paper. Our analysis uses a statistical algorithm, computing, as a function of the initial properties of the fragments (masses and ejection velocities from their parent body), the mean intrinsic probability of impact, and then the mean lifetime of a fragment before impacting the target, as well as the distribution of the relative velocity. For an order{of{magnitude estimate of the available amount of mass, some simple analytical equations have been derived to evaluate the fraction of fragments from the parent body that can reach the target. These formulae allow a preliminary discrimination of the interesting cases. The pair Hyperion{Titan and the Uranus system have been analyzed in detail.

Physical–statistical methods for determining state transition probabilities in mobile‐satellite channel models

AbstractSignal propagation in land mobile satellite (LMS) communication systems has for the last decade become an essential consideration, especially when high‐rate data services are involved. As far as urban or suburban built‐up areas are concerned, the extent of the influence is mainly restricted to the roadside obstacles, since the satellite is positioned at relatively high elevation angles in most practical situations. Probably, the most common model currently used for representing the LMS channel is the Lutz model, which uses two states to represent line‐of‐sight and non‐line‐of‐sight conditions. Transitions between these states are described by transition probabilities which are a function of the environment and the satellite elevation angles. Similarly, an extension to the model allows a four‐state description to be used for the states associated with a pair of satellites used in a dual‐diversity configuration. Calculation of the transition probabilities then requires knowledge of the correlation between the two channels, which in turn depends on the spatial characteristics of the local environment around the mobile.In both cases, the transition probabilities have been derived basically from measurements in the past. In the new approaches described in this paper, physical–statistical principles are applied to construct analytical formulas for the probabilities of shadowing and the correlation between states. These expressions apply particularly to systems operated in built‐up environments, and have been checked against numerical experiments and against direct measurements. In both cases excellent agreement is obtained. Copyright © 2001 John Wiley & Sons, Ltd.

Latitudinally and Seasonally Dependent Zenith-Angle Corrections for Geostationary Satellite IR Brightness Temperatures

Abstract The equivalent brightness temperature Tb recorded by geosynchronous infrared (geo-IR) “window” channel (10.7–11.5 μm) satellite sensors is shown to depend on the zenith angle (local angle from the zenith to the satellite for a pixel’s ground location) in addition to the mix of clouds and surface that would be observed from a direct overhead viewpoint (nadir view). This zenith-angle dependence is characterized, and two corrections are developed from a collection of half-hourly geo-IR pixel data that have been parallax corrected and averaged to a 0.5° × 0.5° latitude/longitude grid for each geosynchronous satellite separately. First, composites of collocated Tb over tropical regions from the Geostationary Operational Environmental Satellite (GOES)-8/GOES-10 and the Meteosat-5/Meteosat-7 satellite pairs are used to produce robust estimates of isotropic zenith-angle corrections as a function of zenith angle and grid-box-averaged Tb. The corrections range from zero for a zenith angle of ∼26.5° to incr...

Photochemical Generation of Polymeric Alkyl-C60 Radicals: ESR Detection and Identification

Electron spin resonance (ESR) spectroscopy has been used to study various alkylfullerene radical adducts generated by UV-photoinitiated reactions between low-density polyethylene (LDPE) and C60 in the presence or absence of benzophenone (BP) as a photoinitiator under different conditions. Photolysis of LDPE/BP/C60 mixture in toluene at 323 K produced benzylfullerene (RC60) radical adducts, showing a strong ESR signal of g = 2.002 70 with several well-resolved pairs of 13C satellites. On the other hand, a well-resolved ESR spectrum characteristic of polymeric alkylfullerene (PC60) radical adducts was observed during UV irradiation of the LDPE/BP/C60 in benzene or in the molten state (413 K). Detailed analyses of hyperfine structures (hfs) revealed that the ESR spectrum for PC60 radical adducts consisted of three components: (1) a broad singlet at g = 2.002 50 arising from C60 radical anions; (2) an innermost pair of 13C satellites; and (3) a 12-line spectrum superimposed on the broad singlet. Spectroscopi...

Population and coherence transfer in half-integer quadrupolar spin systems induced by simultaneous rapid passages of the satellite transitions: A static and spinning single crystal nuclear magnetic resonance study

We have recently shown that utilizing double frequency sweeps (DFSs) instead of pulses can lead to increased efficiencies in population and coherence transfer in half-integer quadrupolar spin systems. Cosine modulation of the carrier amplitude corresponds to the simultaneous irradiation of two frequencies symmetrically around the rf-carrier frequency. Convergent or divergent DFSs can be generated by appropriate time-dependent cosine modulation of the rf field. Population and coherence transfer induced by sweeping the modulation frequency through the quadrupolar satellite transitions is investigated in detail. The time dependence of such passages determines the adiabaticity of the transfer processes. Insight into the involved spin dynamics is of utmost importance in the design and optimization of experiments based on amplitude modulation, such as DFS enhanced multiple-quantum magic angle spanning, where multiple to single-quantum conversion is performed by a DFS. Vega and co-workers have provided a theoretical basis of adiabatic coherence transfer in spin-3/2 systems induced by the combined action of simple time independent cosine amplitude modulation (CAM) of the rf field and sample spinning [Madhu et al., J. Chem. Phys. 112, 2377 (2000)]. In our report we will extend this theory to DFS induced adiabatic transfer phenomena in spin-3/2 and spin-5/2 systems. A fully analytical description will be presented covering the whole adiabaticity range resulting in an accurate description of actual experiments. In this context it will be shown that both population and coherence transfer are governed by the same principles and one unique adiabaticity parameter for each pair of spectral satellites. The transfer phenomena derived for spin-3/2 systems will be studied and quantified experimentally for 23Na in a single crystal of NaNO3. In a static and spinning sample the combination with DFS and CAM irradiation will be studied showing the equivalence of the transfer in all these situations. Further we will demonstrate the greater flexibility of a DFS compared to a CAM pulse to manipulate the adiabaticity and thus to maximize the transfer efficiency. Finally, the 27Al resonance in an α-Al2O3 single crystal will be inspected to demonstrate that the efficiency of DFS-induced population and coherence transfer in spin-5/2 systems depends on the direction of the DFS.

Local GPS tropospheric tomography

A formulation of local GPS tropospheric tomography for determining 4-D distribution of refractivity in the troposphere is presented together with a preliminary analysis of local dense GPS campaign data. Dividing the modeling space up to a height of 10 km above GPS receivers into cells, the refractivity in each cell is estimated in a successive time window by a tomographic reconstruction method in a quite similar manner like the seismic velocity in each cell in Earth’s interior is estimated in seismic tomography. The basic data for tomography are GPS slant delays for respective pairs of station and satellite, which are the sum of postfit phase residual, hydrostatic and wet slant delay. On the other hand, the slant delay from a station to a satellite is expressed by the summation of the product of path length and refractivity in each cell along the ray path. In a given time window, we have numerous observed slant delays corresponding to different ray trajectories, and the refractivity in each cell can be estimated by discrete inversion and least squares methods. The observational equations are usually singular so that we use a damped least squares method popular in seismic tomography. An example of real data analysis is given for the 1995 Shigaraki GPS campaign data, which reveals the spatial and temporal change of refractivity corresponding to the passage of ‘cold front’.

Mutual positions of the Galilean satellites of Jupiter from photometric observations during their mutual occultations and eclipses in 1997

We report the final results of the 1997 campaign of photometric observations of the mutual phenomena of the Galilean satellites carried out at observatories in Kazakhstan, Russia, and Ukraine. Our results contribute substantially to the world data bank of such observations and will allow the model of the motion of Galilean satellites to be further refined. To facilitate the use of photometric data, we reduced them by computing the planetocentric rectangular coordinate differences of satellite pairs for a number of instants of time so we deduce the differences for one instant from one observed light curve. It is these reduced data that constitute the principal result of this work. We based our data reduction on the method which we developed in earlier papers (Emel'yanov 1999; Emel'yanov 2000). The accuracy of observations was estimated in the process of reduction. The paper also describes the equipment used.

An Approach to Novel Complexes with a Tungsten−Phosphorus Triple Bond

The metathesis reaction of [W2(OtBu)6] with tBuCP leads to the phosphido complex [(tBuO)3WP] (1), which can be stabilized when the reaction is carried out in the presence of Lewis acidic carbonyl complexes of the type [M(CO)5thf] (M = Cr, W). However, further reaction of the metathesis products [(tBuO)3WCtBu] and [(tBuO)3WP→M(CO)5] [M = W (4a), Cr (4b)] with tBuCP leads after subsequent 1,3-OtBu shift to the metallaphosphacyclobutadiene derivatives [(tBuO)2W{C(tBu)}2P(OtBu)] (2a) and [(tBuO)2WC(tBu)P{M(CO)5}P(OtBu)] [M = W (5a), M = Cr (5b)]. To prevent the latter, the bulky phosphaalkyne Ar‘CP (Ar‘ = 2,4,6-tBu3C6H2) was employed in the three-component reaction instead of tBuCP. Surprisingly here, a “head-to-tail” dimerization of Ar‘CP occurs to give the novel phosphinidene complexes [M(CO)4P(R‘)C(Ar‘)P{MCO)5}] [M = Cr (6a), M = W (6b); R‘ = 2,4-tBu2-7-Me2-indanyl]. In the case of [W(CO)5thf], additionally, the complex [W(CO)2{(η2-PCAr‘)W(CO)5}2] (7) is formed. The function of [W2(OtBu)6] in this reaction is uncertain, but stoichiometric amounts of [W2(OtBu)6] are essential to obtain complex 6. Reduction of the size of the alkoxide ligands by the use of [W2(ONp)6] (Np = CH2tBu) in the three-component reaction with Ar‘CP leads to the trinuclear cluster compounds [W3(μ3-P){W(CO)5}(μ-ONp)3(ONp)6] (8) and [W3(μ3-P)(μ-ONp)3(ONp)6] (9). The crucial step of the side-product free synthesis of the phosphido complexes 4 is the introduction of MesCP (Mes = 2,4,6-Me3C6H2) into the three-component system of [W2(OtBu)6], RCP, and [W(CO)5thf]. Comprehensive structural and spectroscopic data are given for the products. Furthermore, a 31P NMR experiment was conducted following the reaction of [W2(OtBu)6] with MesCP from −70 °C to ambient temperature. In the range of −60 to −40 °C, a singlet at 845 ppm with one pair of tungsten satellites (1JW,P = 176 Hz) was observed for the complex [(tBuO)3WP] (1).

Synchrotron X-ray diffraction study of phase separation on heating oxidized La 2CuO 4.103(4): the stabilization of phase La 2CuO 4.086(4)

In the present work, the evolution of an oxidised sample of composition La 2CuO 4.103(4) along a thermal treatment has been studied and the stabilisation of a novel phase with a well-defined excess of oxygen has been proven by means of real-time synchrotron X-ray diffraction experiments. The stability of this phase, La 2CuO 4.086(4), seems to be due to the presence of one-dimensional interstitial oxygen ordering along the c-axis, as suggested by the appearance of a pair of superlattice satellite peaks around the mixed parity (012) peak position in a synchrotron X-ray diffractogram collected at 110 K.

Sporadic wind wave horse-shoe patterns

Abstract. The work considers three-dimensional crescent-shaped patterns often seen on water surface in natural basins and observed in wave tank experiments. The most common of these 'horse-shoe-like' patterns appear to be sporadic, i.e., emerging and disappearing spontaneously even under steady wind conditions. The paper suggests a qualitative model of these structures aimed at explaining their sporadic nature, physical mechanisms of their selection and their specific asymmetric form. First, the phenomenon of sporadic horse-shoe patterns is studied numerically using the novel algorithm of water waves simulation recently developed by the authors (Annenkov and Shrira, 1999). The simulations show that a steep gravity wave embedded into widespectrum primordial noise and subjected to small nonconservative effects typically follows the simple evolution scenario: most of the time the system can be considered as consisting of a basic wave and a single pair of oblique satellites, although the choice of this pair tends to be different at different instants. Despite the effective low-dimensionality of the multimodal system dynamics at relatively sho ' rt time spans, the role of small satellites is important: in particular, they enlarge the maxima of the developed satellites. The presence of Benjamin-Feir satellites appears to be of no qualitative importance at the timescales under consideration. The selection mechanism has been linked to the quartic resonant interactions among the oblique satellites lying in the domain of five-wave (McLean's class II) instability of the basic wave: the satellites tend to push each other out of the resonance zone due to the frequency shifts caused by the quartic interactions. Since the instability domain is narrow (of order of cube of the basic wave steepness), eventually in a generic situation only a single pair survives and attains considerable amplitude. The specific front asymmetry is found to result from the interplay of quartic and quintet interactions and non-conservative effects: the growing and grown satellites have a specific value of phase with respect to the basic wave that corresponds to downwind orientation of the convex sides of wave fronts. As soon as the phase relation is violated, the satellite's amplitude quickly decreases down to the noise level.

Combinations of Satellite Crossovers to Study Orbit and Residual Errors in Altimetry

We define combinations of dual‐ and single‐satellite crossover differences to isolate both stationary orbit‐geopotential and non‐geopotential errors in altimetry data. Specifically two types of combinations are found useful. While no combination of differences can resolve the full radial error of single or paired satellites, an approximation of the mean or geographically correlated error of the generally dominant lower orbit of a pair can be found from one kind (substitutions). (The variable part of the error is always available from the single‐satellite crossover differences.) A second useful combination type is found to yield no geopotential orbit error (zeros): uniquely, these can reveal errors in altimetry from imperfect media corrections as well as oceanographic changes in sealevel. The later circumstance is particularly important when the missions for a pair of satellites are disparate in time.

The driving of the plasma sheet by the solar wind

The coupling of the plasma sheet to the solar wind is studied statistically using measurements from various satellite pairs: one satellite in the solar wind and one in either the magnetotail central plasma sheet or the near‐Earth plasma sheet. It is found that the properties of the plasma sheet are highly correlated with the properties of the solar wind: specifically that (1) the density of the plasma sheet is strongly correlated with the density of the solar wind, (2) the temperature of the plasma sheet is strongly correlated with the velocity of the solar wind, (3) the particle pressure and total pressure of the plasma sheet are strongly correlated with the ram pressure of the solar wind, (4) By in the plasma sheet is strongly correlated with the By in the solar wind, (5) Bz in the plasma sheet is weakly correlated with the Bz in the solar wind, (6) Ey in the plasma sheet is weakly correlated with the Ey in the solar wind, and (7) plasma sheet earthward‐tailward flow velocity is weakly anticorrelated with the solar wind velocity. After removing these solar wind dependencies, the dependencies of the properties of the plasma sheet on geomagnetic activity are reduced and changed. The time lags between the solar wind density and the plasma sheet density are investigated statistically and on a case‐by‐case basis; it is found that solar wind material reaches the midtail plasma sheet in ∼2 hours, reaches the near‐Earth nightside plasma sheet in ∼4 hours, and reaches the dayside plasma sheet in ∼15 hours. The pathway for mass transport into the plasma sheet is explored; it is suggested that solar wind material is transported rapidly up the tail to the near‐Earth region via the plasma sheet boundary layer, followed by poloidal transport via convection in the near‐Earth (low β) plasma sheet or followed by eddy diffusion in the not‐too‐distant (high β) plasma sheet. Analogies are drawn between the high Reynolds number plasma sheet and a high Reynolds number fluid wake.

The outer radiation belt during the 10 January, 1997 CME event

On 10 January 1997 a magnetic cloud of a coronal mass ejection impinged upon the earth magnetosphere and caused considerable variations of the relativistic electron population in the earth's outer radiation belt in the following days. Data obtained with radiation detectors on board a pair of satellites, STRV‐1a and STRV‐1b in a nearly equatorial geostationary transfer orbit show that the electron flux variations during the days following the arrival of the magnetic cloud can be characterized by four phases during which the fluxes alternatingly decreased and increased. The close relation between flux and Dst variations suggest the magnetic field variations in the inner magnetosphere to play an important role. However, the observed injection of electrons into the trapping region in the morning of 10 January seems to be crucial for the large electron flux enhancement during the afternoon of 10 January.

The observation of a triangular vortex in a rotating fluid

A dye visualization study of a triangular vortex in a rotating fluid is presented. The emergence and subsequent break-up of the vortex structure are described. Soon after the generation of the triangular vortex it becomes unstable: two satellite vortices merge and pair with the core vortex into an asymmetric dipole, while the third satellite vortex remains behind as a single monopole. A simple point-vortex model is used to simulate this break-up of the triangular vortex. The strengths and positions of the point vortices have been perturbed from an initial steady configuration, consisting of one core vortex surrounded by three oppositely signed satellite vortices, in order to gain insight in the disintegration process of the experimental triangular vortex. It is found that an asymmetry in the strengths of the satellite vortices provides a mechanism that results in an evolution of the vortex structure as observed in the experiment. Both the vortex trajectories and the advection of a passive tracer (dye) are quite well described by the point-vortex model.