Oscillation Recurrence

Table 6.2: Recurrence rates for network pixels (total 5999)

Selection	Block A		Block B		Both Blocks
Criteria	No. pixels	% of total	No. pixels	% of total	No. pixels	% of A	% of B
1700Å
LLO	64	1	103	2	0	-	-
2-3 cycles	4857	81	4611	77	3754	77	81
230-280 s & 2-3 cycles	2090	35	2215	37	818	39	37
230-280 s	3868	64	4138	69	2709	65	70
1600Å
LLO	142	2	93	2	2	1	2
2-3 cycles	4637	77	4913	82	3812	82	78
230-280 s& 2-3 cycles	2430	41	2337	39	961	40	41
230-280 s	4587	76	4465	74	3429	75	77
1216Å
LLO	134	2	123	2	4	3	3
2-3 cycles	5173	86	5126	85	4370	85	84
230-280 s& 2-3 cycles	2537	42	2440	41	1024	40	41
230-280 s	4727	79	4515	75	3584	76	79
1550Å
LLO	131	2	50	1	0	-	-
2-3 cycles	4704	78	3516	59	2085	44	59
230-280 s& 2-3 cycles	2470	41	1591	27	679	27	43
230-280 s	4560	76	3051	51	2324	51	76

By comparing how many pixels in block A of each wavelength display a similar behaviour in block B, it is possible to study whether oscillations of specific period and lifetime occur repeatedly (Table 6.2). At each wavelength all network pixels displaying periodicity between 230-280 s in block A were selected and compared to network pixels containing periodicity in the same range in block B. This showed a recurrence rate of ~65-75% in all four UV passbands. This was also carried out for all network pixels displaying oscillations lasting 2-3 cycles at all periods (where the corresponding value was ~75-85%). A study of all network pixels lasting 2-3 cycles and in the range 230-280 s (i.e., at the peak value in the lifetime-period plots), showed ~40% common pixels. As these oscillations are the most frequent, a 40% chance of a recurrence at the same position represents a good candidate for repeated heating of the surrounding plasma.

Table 6.3: Recurrence rates for internetwork pixels (total 28717)

Selection	Block A		Block B		Both Blocks
Criteria	No. pixels	% of total	No. pixels	% of total	No. pixels	% of A	% of B
1700Å
LLO	642	2	613	2	15	1	1
2-3 cycles	24370	85	26427	92	22420	85	92
230-280 s & 2-3 cycles	13709	48	14518	51	6990	51	48
230-280 s	23871	83	25084	87	20866	87	83
1600Å
LLO	618	2	716	2	18	1	1
2-3 cycles	24078	83	26220	91	21994	91	84
230-280 s & 2-3 cycles	13240	46	13826	48	6337	48	46
230-280 s	23380	81	24640	86	20059	86	81
1216Å
LLO	777	3	836	3	19	1	1
2-3 cycles	26421	92	26334	92	24248	92	92
230-280 s & 2-3 cycles	14499	50	14594	51	7418	51	51
230-280 s	25355	88	25318	88	22364	88	88
1550Å
LLO	462	2	161	1	2	1	1
2-3 cycles	23675	82	15763	55	12985	55	82
230-280 s & 2-3 cycles	12592	44	8128	28	3564	28	44
230-280 s	22245	77	14764	51	11457	52	78

In the internetwork, the fraction of pixels showing oscillations recurring in the same location was generally 5-10% higher than in the network (Table 6.3). The internetwork oscillations lasting 2-3 cycles and in the range 230-280 s (with a ~50% recurrence rate) may be the persistent flashers first identified by Brandt et al. (1992). However their studies suggest grains which are persistent flashers should be 5-10 times less likely to occur than normal K_2V grains, which in turn suggests a recurrence rate of ~10-17%. The higher value of 50% obtained in these data could be due to the internetwork mask preferentially containing persistent flashers rather than normal internetwork grains.