Abstract. 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, X=(−15, −35) R E , 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 R E 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 ∼1 GWb, 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.

[1] According to the loading-unloading substorm scenario, the magnetic flux, stored in the magnetotail during the substorm growth phase,is dissipated in the course of the expansion phase. However so far only separate estimates of both accumulated and dissipated flux values were made due to the lack of methods to calculate those quantities, doing their direct comparison impossible. First, we analyzed the magnetotail magnetic flux at substorm onset as a function of solar wind parameters to show that the tail magnetic flux, stored during the growth phase (DF T ), depends mainly (CC = 0.95) on the merging electric field E m = V SW B t sin 3 q/2. It implies the lack of threshold magnetic flux at substorm onset. Also, the magnetic flux through the auroral bulge at substorm maximum (

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Recently, it was argued that Hall conductivity and peak intensity of equivalent ionospheric currents are sensitive to the amount of field-aligned acceleration of plasma sheet (PS) electrons, which in turn depends on the plasma sheet parameters T e and N e (electron temperature and density) proportionally to the quantity eTN = (T e) 1/2 /N e. Here we extend these studies using data from six tail seasons of THEMIS observations to show statistically that the behavior of these PS electron parameters, measured in the middle of the nightside plasma sheet at~10 R E distance, depends in a very different way on two basic processes: the solar wind state and substorms. We confirm previous work that slow/dense (fast/tenuous) solar wind provides cold/dense (hot/tenuous) plasma sheet conditions. However, we find that electron temperature and pressure parameters (T e and P e) behave differently from the proton ones (T p and P p), indicating a strong decoupling between temperature variations of auroral protons and electrons in the central plasma sheet (CPS): electrons are more sensitive to the substorm-related acceleration in the magnetotail than protons. Our superposed epoch study of plasma sheet parameter variations during substorms as well as our analysis of plasma acceleration at dipolarization fronts shows that during the substorm expansion phase a new (accelerated and plasma-depleted) population comes into the inner CPS with the flow bursts, showing an average increase of electron temperature and eTN parameter roughly by a factor of 2 above its background values for both cold/dense and hot/tenuous plasma sheet states. Preferential electron heating in the flow bursts is also statistically confirmed.