Table 1: IRIS duty cycles (%). (a) annual IRIS; (b) annual partial gap filled IRIS; (c) 4-month summer IRIS ; (d) 4-month summer partial gap filled IRIS. (NB: (1) Values for 1989 start the 1st July. For the 4-month duty cycle values, only July, August and September are used / (2) Values for 1999 ending 30 August. For the 4-month duty cycle values, only June, July and August are used.).

Years	a	b	c	d
1989	34.5	58.0	50.6	77.6
1990	33.9	60.6	52.6	84.1
1991	41.0	70.3	57.3	88.1
1992	38.9	68.0	54.4	85.8
1993	33.6	62.4	41.7	74.7
1994	43.2	70.3	64.7	89.9
1995	47.4	75.8	67.7	92.6
1996	41.3	71.1	53.6	84.8
1997	35.4	61.8	44.5	71.7
1998	28.9	53.8	33.9	57.5
1999	17.1	33.4	19.9	40.5