  Variability on all time scales between seconds and decades is typical for
cataclysmic variables (CVs). One of the brightest and best studied CVs is TT
Ari, a nova-like variable which belongs to the VY Scl subclass, characterized
by occasional low states in their light curves. It is also known as a permanent
superhumper at high state, revealing "positive" (P_S > P_0) as well as
"negative" (P_S < P_0) superhumps, where P_S is the period of the superhump and
P_0 the orbital period. TT Ari was observed by the Canadian space telescope
MOST for about 230 hours nearly continuously in 2007, with a time resolution of
48 seconds. Here we analyze these data, obtaining a dominant "negative"
superhump signal with a period P_S = 0.1331 days and a mean amplitude of 0.09
mag. Strong flickering with amplitudes up to 0.2 mag and peak-to-peak time
scales of 15-20 minutes is superimposed on the periodic variations. We found no
indications for significant quasi-periodic oscillations with periods around 15
minutes, reported by other authors. We discuss the known superhump behaviour of
TT Ari during the last five decades and conclude that our period value is at
the upper limit of all hitherto determined "negative" superhump periods of TT
Ari, before and after the MOST run.
