Estimating the net plasma loss from ionospheric outflow 

S. Haaland,
E. Engwall,
A. Eriksson, 
M. F"\orster,
B. Lybekk,
A. Pedersen,
K. Svenes

An important source of magnetospheric plasma is outflow from the 
terrestrial ionosphere. Low energy ions travel along the magnetic 
field lines and enter the magnetospheric lobes and are convected
towards the tail plasma sheet. Recent results from Cluster indicate 
that the field aligned outflow velocitiy is sometimes much higher 
than the convection towards the central plasma sheet. A substantial 
amount of plasma therefore escape downtail without ever reaching the 
central plasma sheet.
In this work, we use a Cluster measurements of the ionospheric outflow 
and lobe convection velocities combined with models of the magnetic field 
and plasma composition in an attempt to quantify the plasma loss for 
various magnetospheric conditions. Preliminary results show that both 
the circulation of plasma but also the tailward escape of ions 
increase significantly during disturbed magnetospheric conditions.