28 research outputs found
Corrigendum to "Time-varying magnetotail magnetic flux calculation: a test of the method" published in Ann. Geophys., 27, 1583–1591, 2009
No abstract available
Quantitative magnetotail characteristics of different magnetospheric states
Quantitative relationships allowing one to compute the lobe magnetic field, flaring angle and tail radius, and to evaluate magnetic flux based on solar wind/IMF parameters and spacecraft position are obtained for the middle magnetotail, <i>X</i>=(–15,–35)<i>R<sub>E</sub></i>, using 3.5 years of simultaneous Geotail and Wind spacecraft observations. For the first time it was done separately for different states of magnetotail including the substorm onset (SO) epoch, the steady magnetospheric convection (SMC) and quiet periods (Q). In the explored distance range the magnetotail parameters appeared to be similar (within the error bar) for Q and SMC states, whereas at SO their values are considerably larger. In particular, the tail radius is larger by 1–3 <i>R<sub>E</sub></i> at substorm onset than during Q and SMC states, for which the radius value is close to previous magnetopause model values. The calculated lobe magnetic flux value at substorm onset is ~1GWb, exceeding that at Q (SMC) states by ~50%. The model magnetic flux values at substorm onset and SMC show little dependence on the solar wind dynamic pressure and distance in the tail, so the magnetic flux value can serve as an important discriminator of the state of the middle magnetotail.<br><br> <b>Key words.</b> Magnetospheric physics (solar windmagnetosphere- interactions, magnetotail, storms and substorms
In situ magnetotail magnetic flux calculation
We explore two new modifications of the magnetotail magnetic flux
(<i>F</i>) calculation algorithm based on the
Petrinec and Russell (1996) (PR96) approach of the tail
radius determination. Unlike in the PR96 model, the tail radius
value is calculated at each time step based on simultaneous
magnetotail and solar wind observations. Our former algorithm,
described in Shukhtina et al. (2009), required that the "tail
approximation" requirement were fulfilled, i.e., it could be applied only
tailward <i>x</i> ∼ −15 <i>R</i><sub><i>E</i></sub>. The new modifications take into account
the approximate uniformity of the magnetic field of external
sources in the near and middle tail. Tests, based on magnetohydrodynamics
(MHD) simulations, show that this approach may be applied at smaller
distances, up to <i>x</i> ∼ −3 <i>R</i><sub><i>E</i></sub>. The tests also show that the
algorithm fails during long periods of strong positive interplanetary magnetic field (IMF) <i>B<sub>z</sub></i>.
A new empirical formula has also been obtained for the tail
radius at the terminator (at <i>x</i> = 0) which improves the
calculations
Time-varying magnetotail magnetic flux calculation: a test of the method
We modified the Petrinec and Russell (1996) algorithm to allow the
computation of time-varying magnetotail magnetic flux based on simultaneous
spacecraft measurements in the magnetotail and near-Earth solar wind. In
view of many assumptions made we tested the algorithm against MHD simulation
in the artificial event, which provides the input from two artificial
spacecraft to compute the magnetic flux F values with our algorithm; the
latter are compared with flux values, obtained by direct integration in the
tail cross-section. The comparison shows similar time variations of
predicted and simulated fluxes as well as their good correlation (cc>0.9)
for the input taken from the tail lobe, which somewhat degrades if using the
"measurements" from the central plasma sheet. The regression relationship
between the predicted and computed flux values is rather stable allowing one
to correct the absolute value of predicted magnetic flux.
We conclude that this method is a perspective tool to monitor the tail
magnetic flux which is one of the main global magnetotail parameters
Average characteristics of the midtail plasma sheet in different dynamic regimes of the magnetosphere
We study average characteristics of plasma sheet convection in the middle
tail during different magnetospheric states (Steady Magnetospheric
Convection, SMC, and substorms) using simultaneous magnetotail (Geotail,
15-35 RE downtail) and solar wind (Wind spacecraft) observations during
3.5 years. (1) A large data set allowed us to obtain the average values of the
plasma sheet magnetic flux transfer rate (Ey and directly compare it
with the dayside transfer rate (Emod for different magnetospheric
states. The results confirm the magnetic flux imbalance model suggested by
Russell and McPherron (1973), namely: during SMC periods the day-to-night
flux transport rate equals the global Earthward plasma sheet convection;
during the substorm growth phase the plasma sheet convection is suppressed
on the average by 40%, whereas during the substorm expansion phase it twice
exceeds the day-to-night global flux transfer rate. (2) Different types of
substorms were revealed. About 1/3 of all substorms considered displayed
very weak growth in the tail lobe magnetic field before the onset. For these
events the plasma sheet transport was found to be in a balance with the
day-to-night flux transfer, as in the SMC events. However, the lobe
magnetic field value in these cases was as large as that in the substorms
with a classic growth phase just before the onset (both values exceed the
average level of the lobe field during the SMC). Also, in both groups similar
configurational changes (magnetic field stretching and plasma sheet
thinning) were observed before the substorm onset. (3) Superimposed epoch
analysis showed that the plasma sheet during the late substorm recovery phase
has the characteristics similar to those found during SMC events, the SMC
could be a natural magnetospheric state following the substorm
Comparison of magnetotail magnetic flux estimates based on global auroral images and simultaneous solar wind—magnetotail measurements
We compared simultaneous magnetotail magnetic flux F estimates, (1) based on in situ spacecraft measurements in the tail and solar wind (F[SUB]T[/SUB]) with (2) the polar cap magnetic flux, estimated from global auroral images (using proton-induced or electron-induced emissions, F[SUB]p[/SUB] or F[SUB]e[/SUB], respectively). Simultaneous F[SUB]p[/SUB] and F[SUB]e[/SUB] estimates gave the correlation coefficient CC=0.74, indicating that these measures are not absolutely precise. Regression analysis of F[SUB]T[/SUB] versus F[SUB]e[/SUB] and F[SUB]p[/SUB] gave CC values 0.73 and 0.50, correspondingly. F[SUB]T[/SUB] values, containing closed magnetic flux, are systematically higher than F[SUB]p[/SUB] and F[SUB]e[/SUB] by 20-30%. Motivated by diverse results, published by different groups, we reanalyzed the F dependence on the dayside merging electric field E[SUB]m[/SUB] for different dynamical states. The linear regression F(E[SUB]m[/SUB]) for substorm onsets shows a large slope ˜0.07-0.12GWb/(mV/m) for all F[SUB]p[/SUB], F[SUB]e[/SUB] and F[SUB]T[/SUB], confirming the loading-unloading substorm scheme. For SMC intervals this slope is only 0.03 GWb/(mV/m)