Time scales of sand suspending by irregular waves  <B>Time scales of sand suspending by irregular waves</B><P>N.V. Pykhov1, R.D. Kos'yan2 and S.Yu. Kuznetsov</B><I><P> 1 P.P. Shirshov Oceanology Institute, Russian Academy of Sciences, Moscow, Russia <BR> 2 The Southern Branch of the P.P. Shirshov Oceanology Institute, Russian Academy of Sciences, Gelendzhik7, Russia</I><P> Abstract<P> On the basis of field experiment conducted in 1993 in the Black Sea the time scales and mechanisms of sand suspending by irregular waves are discussed. Synchronous measurements of suspended sediment concentration in the water layer of 48 cm above the bottom and two horizontal velocity components at the depth of 30 cm were done near the top of the submerged bar for different wave regimes. The fluctuation of concentration of suspended sand in gravity and infragravity frequency bands are discussed in some cases: a) When the waves were slightly deformed and the bottom was covered with two dimensional vortex ripples; b) When nearbottom velocities increase and twodimensional ripples are transformed into threedimensional ones; c) When the breaking of the largest waves begins and ripples are in the phase of their obliteration; d) When there is a mass wave breaking and the bottom is smooth.<P>