  The EUSO-TA ground-based fluorescence detector of the JEM-EUSO program, which
operates at the Telescope Array (TA) site in Utah (USA), is being upgraded. In
the previous data acquisition campaigns, it detected the first nine ultra-high
energy cosmic ray events with the external trigger provided by the Black Rock
Mesa fluorescence detectors of the Telescope Array (TA-BRM-FDs). Among the
upgrades, there is the installation of a trigger algorithm for the independent
detection of cosmic ray air showers and upgraded electronics. A simulation
study was developed to understand the performance of EUSO-TA in the new setup
and different background conditions. This study allowed us to estimate the
detection limit of the ground-based detector, which can be used to extrapolate
the detection limit for a balloon-based detector. Moreover, it provided
estimations of the expected trigger rates for ultra-high energy cosmic rays. In
this work, the description of the simulation setup, the method developed to
rescale the energy of the cosmic rays to account for the portion of air shower
actually observed rather than the whole one, and the results in terms of
detection limit and trigger rates, are reported.
