Solar wind interactions with Comet 19P/Borrelly     

D.T Young  F.J Crary  J.E Nordholt  D Boice  A Eviatar  J.J Hanley  D.J McComas  D Reisenfeld  R.C Wiens 《Icarus》2004,167(1):80-88

The Plasma Experiment for Planetary Exploration (PEPE) made detailed observations of the plasma environment of Comet 19P/Borrelly during the Deep Space 1 (DS1) flyby on September 22, 2001. Several distinct regions and boundaries have been identified on both inbound and outbound trajectories, including an upstream region of decelerated solar wind plasma and cometary ion pickup, the cometary bow shock, a sheath of heated and mixed solar wind and cometary ions, and a collisional inner coma dominated by cometary ions. All of these features were significantly offset to the north of the nucleus-Sun line, suggesting that the coma itself produces this offset, possibly because of well-collimated large dayside jets directed 8°-10° northward from the nucleus as observed by the DS1 MICAS camera. The maximum observed ion density was 1640 ion/cm³ at a distance of 2650 km from the nucleus while the flow speed dropped from 360 km/s in the solar wind to 8 km/s at closest approach. Preliminary analysis of PEPE mass spectra suggest that the ratio of CO⁺/H₂O⁺ is lower than that observed with Giotto at 1P/Halley.  相似文献   

Ion and neutral sources and sinks within Saturn's inner magnetosphere: Cassini results     

E.C. Sittler Jr.  N. Andre  M. Burger  A. Coates  D. Reisenfeld  A. Persoon  H.T. Smith  R.E. Hartle  M.D. Shappirio  D.J. McComas 《Planetary and Space Science》2008,56(1):3-18

Using ion-electron fluid parameters derived from Cassini Plasma Spectrometer (CAPS) observations within Saturn's inner magnetosphere as presented in Sittler et al. [2006a. Cassini observations of Saturn's inner plasmasphere: Saturn orbit insertion results. Planet. Space Sci., 54, 1197-1210], one can estimate the ion total flux tube content, N_IONL², for protons, H⁺, and water group ions, W⁺, as a function of radial distance or dipole L shell. In Sittler et al. [2005. Preliminary results on Saturn's inner plasmasphere as observed by Cassini: comparison with Voyager. Geophys. Res. Lett. 32(14), L14S04), it was shown that protons and water group ions dominated the plasmasphere composition. Using the ion-electron fluid parameters as boundary condition for each L shell traversed by the Cassini spacecraft, we self-consistently solve for the ambipolar electric field and the ion distribution along each of those field lines. Temperature anisotropies from Voyager plasma observations are used with (T_⊥/T_∥)_W⁺∼5 and (T_⊥/T_∥)_H⁺∼2. The radio and plasma wave science (RPWS) electron density observations from previous publications are used to indirectly confirm usage of the above temperature anisotropies for water group ions and protons. In the case of electrons we assume they are isotropic due to their short scattering time scales. When the above is done, our calculation show N_IONL² for H⁺ and W⁺ peaking near Dione's L shell with values similar to that found from Voyager plasma observations. We are able to show that water molecules are the dominant source of ions within Saturn's inner magnetosphere. We estimate the ion production rate S_ION∼10²⁷ ions/s as function of dipole L using N_H⁺, N_W⁺ and the time scale for ion loss due to radial transport τ_D and ion-electron recombination τ_REC. The ion production shows localized peaks near the L shells of Tethys, Dione and Rhea, but not Enceladus. We then estimate the neutral production rate, S_W, from our ion production rate, S_ION, and the time scale for loss of neutrals by ionization, τ_ION, and charge exchange, τ_CH. The estimated source rate for water molecules shows a pronounced peak near Enceladus’ L shell L∼4, with a value S_W∼2×10²⁸ mol/s.  相似文献   

RING CURRENT DYNAMICS DURING THE 13–18 JULY 2000 STORM PERIOD     

Jordanova  V.K.  Thorne  R.M.  Farrugia  C.J.  Dotan  Y.  Fennell  J.F.  Thomsen  M.F.  Reeves  G.D.  McComas  D.J. 《Solar physics》2001,204(1-2):361-375

We study the development of the terrestrial ring current during the time interval of 13–18 July, 2000, which consisted of two small to moderate geomagnetic storms followed by a great storm with indices Dst=−300 nT and Kp=9. This period of intense geomagnetic activity was caused by three interplanetary coronal mass ejecta (ICME) each driving interplanetary shocks, the last shock being very strong and reaching Earth at ∼ 14 UT on 15 July. We note that (a) the sheath region behind the third shock was characterized by B _z fluctuations of ∼35 nT peak-to-peak amplitude, and (b) the ICME contained a negative to positive B _z variation extending for about 1 day, with a ∼ 6-hour long negative phase and a minimum B _z of about −55 nT. Both of these interplanetary sources caused considerable geomagnetic activity (Kp=8 to 9) despite their disparity as interplanetary triggers. We used our global ring current-atmosphere interaction model with initial and boundary conditions inferred from measurements from the hot plasma instruments on the Polar spacecraft and the geosynchronous Los Alamos satellites, and simulated the time evolution of H⁺, O⁺, and He⁺ ring current ion distributions. We found that the O⁺ content of the ring current increased after each shock and reached maximum values of ∼ 60% near minimum Dst of the great storm. We calculated the growth rate of electromagnetic ion cyclotron waves considering for the first time wave excitation at frequencies below O⁺ gyrofrequency. We found that the wave gain of O⁺ band waves is greater and is located at larger L shells than that of the He⁺ band waves during this storm interval. Isotropic pitch angle distributions indicating strong plasma wave scattering were observed by the imaging proton sensor (IPS) on Polar at the locations of maximum predicted wave gain, in good agreement with model simulations.  相似文献   

ACE Observations of the Bastille Day 2000 Interplanetary Disturbances     

Smith  C.W.  Ness  N.F.  Burlaga  L.F.  Skoug  R.M.  McComas  D.J.  Zurbuchen  T.H.  Gloeckler  G.  Haggerty  D.K.  Gold  R.E.  Desai  M.I.  Mason  G.M.  Mazur  J.E.  Dwyer  J.R.  Popecki  M.A.  Möbius  E.  Cohen  C.M.S.  Leske  R.A. 《Solar physics》2001,204(1-2):227-252

We present ACE observations for the six-day period encompassing the Bastille Day 2000 solar activity. A high level of transient activity at 1 AU, including ICME-driven shocks, magnetic clouds, shock-accelerated energetic particle populations, and solar energetic ions and electrons, are described. We present thermal ion composition signatures for ICMEs and magnetic clouds from which we derive electron temperatures at the source of the disturbances and we describe additional enhancements in some ion species that are clearly related to the transient source. We describe shock acceleration of 0.3–2.0 MeV nucl⁻¹ protons and minor ions and the relative inability of some of the shocks to accelerate significant energetic ion populations near 1 AU. We report the characteristics of < 20 MeV nucl⁻¹ solar energetic ions and < 0.32 MeV electrons and attempt to relate the release of energetic electrons to particular source regions.  相似文献   

Cassini observations of Saturn's inner plasmasphere: Saturn orbit insertion results     

E.C. Sittler Jr.  M. Thomsen  R.E. Hartle  D. Chornay  D. Simpson  A.J. Coates  D.J. McComas  D. Reisenfeld  N. Andre 《Planetary and Space Science》2006,54(12):1197-1210

We present new and definitive results of Cassini plasma spectrometer (CAPS) data acquired during passage through Saturn's inner plasmasphere by the Cassini spacecraft during the approach phase of the Saturn orbit insertion period. This analysis extends the original analysis of Sittler et al. [2005. Preliminary results on Saturn's inner plasmasphere as observed by Cassini: comparison with Voyager. Geophys. Res. Lett. 32, L14S07, doi:10.1029/2005GL022653] to L∼10 along with also providing a more comprehensive study of the interrelationship of the various fluid parameters. Coincidence data are sub-divided into protons and water group ions. Our revised analysis uses an improved convergence algorithm which provides a more definitive and independent estimate of the spacecraft potential Φ_SC for which we enforce the protons and water group ions to co-move with each other. This has allowed us to include spacecraft charging corrections to our fluid parameter estimations and allow accurate estimations of fluctuations in the fluid parameters for future correlative studies. In the appendix we describe the ion moments algorithm, and minor corrections introduced by not weighting the moments with sinθ term in Sittler et al. [2005] (Correction offset by revisions to instruments geometric factor). Estimates of the spacecraft potential and revised proton densities are presented. Our total ion densities are in close agreement with the electron densities reported by Moncuquet et al. [2005. Quasi-thermal noise spectroscopy in the inner magnetosphere of Saturn with Cassini/RPWS: electron temperatures and density. Geophys. Res. Lett. 32, L20S02, doi:10.1029/2005GL022508] who used upper hybrid resonance (UHR) emission lines observed by the radio and plasma wave science (RPWS) instrument. We show a positive correlation between proton temperature and water group ion temperature. The proton and thermal electron temperatures track each with both having a positive radial gradient. These results are consistent with pickup ion energization via Saturn's rotational electric field. We see evidence for an anti-correlation between radial flow velocity V_R and azimuthal velocity V_φ, which is consistent with the magnetosphere tending to conserve angular momentum. Evidence for MHD waves is also present. We show clear evidence for outward transport of the plasma via flux tube interchange motions with the radial velocity of the flow showing positive radial gradient with functional dependence for 4<L<10 (i.e., if we assume to be diffusive transport then D_LL∼D₀L¹¹ for fixed stochastic time step δt). Previous models with centrifugal transport have used D_LL∼D₀L³ dependence. The radial transport seems to begin at Enceladus’ L shell, L∼4, where we also see a minimum in the W⁺ ion temperature . For the first time, we are measuring the actual flux tube interchange motions in the magnetosphere and how it varies with radial distance. These observations can be used as a constraint with regard to future transport models for Saturn's magnetosphere. Finally, we evaluate the thermodynamic properties of the plasma, which are all consistent with the pickup process being the dominant energy source for the plasma.  相似文献   

IBEX-Lo observations of energetic neutral hydrogen atoms originating from the lunar surface     

D.F. Rodríguez M.  L. Saul  P. Wurz  S.A. Fuselier  H.O. Funsten  D.J. McComas  E. Möbius 《Planetary and Space Science》2012,60(1):297-303

In this paper we present quantitative results of observations of energetic neutral atoms (ENAs) originating from the lunar surface. These ENAs, which are hydrogen atoms, are the result of the solar wind protons being reflected from and neutralised at the surface of the Moon. These measurements were made with IBEX-Lo on NASA's IBEX satellite. From these measurements we derive the energy spectrum of the ENAs, their flux, and the lunar albedo for ENAs (i.e., the ratio of ENAs to the incoming solar wind protons). The energy spectra of the ENAs clearly show that their origin is directly from the solar wind via backscattering, and that they are not sputtered atoms. From several observation periods we derived an average global albedo of A_H=0.09±0.05. From the observed energy spectra we derive a generic spectrum for unshielded bodies in the solar wind.  相似文献   

A Landscape-Scale Assessment of Above- and Belowground Primary Production in Coastal Wetlands: Implications for Climate Change-Induced Community Shifts     

Camille L. Stagg  Donald R. SchoolmasterJr.  Sarai C. Piazza  Gregg Snedden  Gregory D. Steyer  Craig J. Fischenich  Robert W. McComas 《Estuaries and Coasts》2017,40(3):856-879

Above- and belowground production in coastal wetlands are important contributors to carbon accumulation and ecosystem sustainability. As sea level rises, we can expect shifts to more salt-tolerant communities, which may alter these ecosystem functions and services. Although the direct influence of salinity on species-level primary production has been documented, we lack an understanding of the landscape-level response of coastal wetlands to increasing salinity. What are the indirect effects of sea-level rise, i.e., how does primary production vary across a landscape gradient of increasing salinity that incorporates changes in wetland type? This is the first study to measure both above- and belowground production in four wetland types that span an entire coastal gradient from fresh to saline wetlands. We hypothesized that increasing salinity would limit rates of primary production, and saline marshes would have lower rates of above- and belowground production than fresher marshes. However, along the Northern Gulf of Mexico Coast in Louisiana, USA, we found that aboveground production was highest in brackish marshes, compared with fresh, intermediate, and saline marshes, and belowground production was similar among all wetland types along the salinity gradient. Multiple regression analysis indicated that salinity was the only significant predictor of production, and its influence was dependent upon wetland type. We concluded that (1) salinity had a negative effect on production within wetland type, and this relationship was strongest in the fresh marsh (0–2 PSU) and (2) along the overall landscape gradient, production was maintained by mechanisms at the scale of wetland type, which were likely related to plant energetics. Regardless of wetland type, we found that belowground production was significantly greater than aboveground production. Additionally, inter-annual variation, associated with severe drought conditions, was observed exclusively for belowground production, which may be a more sensitive indicator of ecosystem health than aboveground production.  相似文献   

Responding to flood risk in Louisiana: the roles of place attachment,emotions, and location     

Holley  Jason R.  McComas  Katherine A.  Lambert  Catherine E.  Snider  Natalie P.  Tucker  Grace K. 《Natural Hazards》2022,113(1):615-640

Natural Hazards - Drawing from protection motivation theory (PMT), we examined how place attachment and negative emotions, alongside threat and coping appraisals, personal experiences, and...  相似文献   

MAGNETIC FLUX TUBES AT 3 AU?     

Parenti  S.  Velli  M.  Poletto  G.  Suess  S. T.  McComas  D. J. 《Solar physics》1997,174(1-2):329-340

We present an analysis of plasma and magnetic field data acquired by the Ulysses spacecraft on May 1994. Our study is motivated by the result of Poletto et al. (1996) who found some evidence for a peak in the power spectrum of magnetic pressure at a frequency 2 × 10–⁵ Hz, during that period. A re-evaluation of the plasma pressure power spectrum, on the basis of better data than used in the previous work, gives only marginal evidence for a peak at that frequency. If both spectra had excess power in the same spectral range, one might hypothesize that the Pressure Balanced Structures (PBS) detected in the data trace periodically distributed coronal structures which maintain their identity up to large distances. A careful data analysis, however, shows that this interpretation is hardly tenable. Hence, we consider the alternative hypotheses that the observed PBS are either a bundle of magnetic flux tubes, with no characteristic periodicity, in pressure equilibrium with the ambient, or the manifestation, at large distances, of waves generated close to the Sun. To prove the latter case, we made a test simulation of the evolution with heliocentric distance of an ensemble of Alfvén and slow mode waves, generated close to the Sun, and show that structures similar to those we analyzed may form in the interplanetary medium. Our simulations also seem to show that together with PBS, magnetic holes, frequently observed in the Ulysses data, could also originate from the nonlinear evolution of large amplitude slow waves in quasi-perpendicular propagation. We conclude that the observed PBS most likely arise via an in situ generation mechanism, rather than being remnants of solar structures.  相似文献   

Heliolatitude and Time Variations of Solar Wind Structure from in situ Measurements and Interplanetary Scintillation Observations     

J. M. Sokół  M. Bzowski  M. Tokumaru  K. Fujiki  D. J. McComas 《Solar physics》2013,285(1-2):167-200

The 3D structure of the solar wind and its evolution in time are needed for heliospheric modeling and interpretation of energetic neutral atoms observations. We present a model to retrieve the solar wind structure in heliolatitude and time using all available and complementary data sources. We determine the heliolatitude structure of solar wind speed on a yearly time grid over the past 1.5 solar cycles based on remote-sensing observations of interplanetary scintillations, in situ out-of-ecliptic measurements from Ulysses, and in situ in-ecliptic measurements from the OMNI 2 database. Since in situ out-of-ecliptic information on the solar wind density structure is not available apart from the Ulysses data, we derive correlation formulae between the solar wind speed and density and use the information on the solar wind speed from interplanetary scintillation observations to retrieve the 3D structure of the solar wind density. With the variations of solar wind density and speed in time and heliolatitude available, we calculate variations in solar wind flux, dynamic pressure, and charge-exchange rate in the approximation of stationary H atoms.  相似文献