Mt. Washington Forbush decreases -- dn/n% less than 3% are not included. YYYYMMDD % decrease Remarks (daily averages) ================================================================================================================ 1954 None observed. 19551121 3.2 Hourly, 5.4%; max rate >1%/hour; Ref 1. 19560108 13 to = 28 d; 1.9% < predecrease level. 19560302 5 Hourly, 6.9%; max rate >1.5%/hr; Ref 1; 4 days to next FD. 19560312 4.7 to = 17 days. 19560317 3.2 No recovery before next FD. 19560428 4.9 19560514 4.5 19560817 3 19560831 5.8 Hourly, 6.5%; max rate 1.7%/hour; Ref 1. 19560922 3 19561108 7.5 Hourly 8.3%; max rate 2.2%/hour; incomplete recovery before next FD. 19561227 4.1 19570121 15.3 Maximum rate 2.5%/hour; Ref 1, 5. 19570310 8.2 19570415 9.4 19570623 4.7 19570805 7 19570829 13.7 Maximum rate 2.6%/hour; classic FD; precursor; rigidity dependence; Ref 1, 5. 19570922 5.2 19570929 5 19571023 9.3 Reference 1. 19571123 8.5 19571217 6.9 19580117 5.1 19580211 5.2 Spec. FD; max rate 7%/hour; Ref 1, 5. 19580326 7.6 Reference 1. 19580529 4.4 19580629 3.4 19580709 6.1 Hourly, 7.8%; maximum rate 1.7%/hour; Ref 1. 19580817 5.1 Reference 1 19580824 5.6 Reference 1. 19580915 4.4 19581001 3.3 19581022 5.3 19581110 3.9 19581214 3.7 19590128 3.3 19590213 8.4 19590226 4.5 19590411 3.2 19590424 3 19590512 12.8 Hourly, 14.8%; maximum rate 5%/hour; rigidity dependence; Ref. 1, 5. 19590711 8.7 Hourly 9.9%; maximum rate 3.2%/hour; Ref 1, 5. 19590715 11.6 Hourly, 14.5%; maximum rate 6.1%/hour; Ref 1. 19590717 10.7 Hourly, 13.5%; maximum rate 4.5%/hour; Ref 1. 19590820 6.5 Maximum rate 2.5%/hour; Ref 1. 19590904 4.3 19590919 3.8 19591203 6.4 19591222 3.3 19600113 4.3 19600330 10.6 19600430 7.5 19600509 3.9 19600524 3.4 19600530 3.5 19600606 3 19600630 6.1 19600716 3.4 19600830 3 19601007 6.1 19601025 3.6 19601116 14.2 19601227 3.1 19610217 3.2 19610413 3.7 19610712 10.6 19610718 5.9 19610727 4.6 19610930 6.6 19611029 3.1 19611201 4.4 19620422 3 19630503 3.4 19630915 3 19630922 9.4 19631028 3 1964 None observed. 19651006 3.1 19660323 5.3 Reference 5. 19660830 7.2 19660905 3.4 19660913 4 Reference 5. 19660924 3.7 19661214 3.1 19670113 3.9 19670502 3.1 19670526 7.5 19670607 3 19671028 5.4 19680126 4.1 Unusual FD; Reference 3, 5. 19680405 4.4 Slow FD; Reference 7. 19680611 4.1 Reference 7. 19680712 4.1 19680822 3 19681001 3.7 19681028 11.1 19681117 3.8 19681206 4.9 19690228 6.6 19690317 3.3 19690324 6.8 19690413 5.3 19690428 3.1 19690514 6.1 Reference 7. 19690609 4.9 Rigidity dependence, 11 year mod. changed after FD; Ref 4. 19690928 6 19691108 4.1 19691127 3 19700128 3.7 19700404 4.1 19700606 3.7 19700617 4.8 19700724 5.2 19700816 4.8 19700909 4.3 19701106 6.5 19701111 5.7 19710127 3.2 19710416 3.3 19711007 3.6 19711121 5 19711215 5.6 19720117 3 19720309 3.2 19720517 3.9 19720617 5 Reference 7, 10. 19720804 18.7 Two phases; 8.8%/5hours and 24.5%/5hours, Ref 6. 19721031 7.8 Reference 7, 10. 19730119 3.2 19730413 4.8 19730514 3.3 19740507 5.4 Reference 10. 19740704 5.6 19740910 6.3 1975 None observed. 19760330 7.6 19770911 3.9 19770921 5.4 19780103 4.5 19780130 3.9 19780214 12.6 20%/10 hours; classic FD; several days IMP data missing; Voyager 1 and 2 at 2.3 AU, Ref 10, 11. 19780306 7.4 Reference 10, 11. 19780411 3 19780418 3.6 19780430 18.1 Large gaps in IMP data-solar flares. 19780529 7.5 19780603 3.3 19780625 5.6 Reference 10. 19780713 7.2 Relatively slow decrease; 0.4%/hour for 14 hours; Ref 10, 11. 19780826 7.2 Reference 10. 19781110 3.9 Reference 18. 19781221 3.3 19790223 6.2 19790328 3.4 Reference 11. 19790424 5.8 Reference 11, 18. 19790606 6 Reference 10, 11, 18. 19790707 7.8 Reference 10, 11. 19790818 7.8 Reference 18. 19791007 5.3 Reference 10. 19791110 5.2 Reference 10. 19800206 5.3 Reference 10. 19800305 3.2 19800402 6.9 Reference 10, 11, 18. 19800606 7.4 Reference 10, 11. 19800625 4.1 19800726 3.5 Reference 10. 19801027 3.2 Reference 18. 19801111 4.5 Reference 10, 11, 18. 19801130 8.3 Slow, asymmetrical decrease; Ref 18. 19801220 3.5 19810201 6 Reference 10. 19810224 11.3 Slow decrease, U shaped; Ref 11. 19810327 4 19810516 6.4 Reference 18, large variations during this period. 19810604 3.5 19810723 9.1 Reference 10, 11. 19810809 4.1 19811003 4.2 19811012 5.7 Reference 11, 18. 19811111 3.9 19811224 3.2 19820130 8 Reference 10, 18. 19820211 5.1 Reference 10. 19820228 5 19820425 3.8 19820606 9.7 Slow decrease with incomplete recovery; Ref 10, 11. 19820710 25 Preliminary decrease: 5%/12 hours; main phase: 23.2%/9 hours; IMP8 about 55%; IMP data good; Ref 11, 18. 19820808 3.7 19820905 7 Reference 18. 19820918 9 Two phases(?); looks like 1/26/68; Ref 18. 19821124 8.1 Hourly data missing; second decrease about 30 Nov 7.8%/9 hours. 19821210 5.1 4.0%/5 hours; no recovery for 12 days. 19830110 5.1 Reference 11. 19830204 7 Slow decrease, about 7%/12 hours; full recovery; Ref 11. 19830510 3.7 19830609 3.6 19840504 5.3 19840703 5.5 19840912 5.7 19850425 6.4 Slow decrease, about 24 hours; full recovery. 19860206 9.8 Classic FD; seen at all spacecraft; recovery phase: 8%/7 hours; few days missing at IMP8. 19860308 3.1 19861103 4.1 Classic FD; IMP data complete; fast phase: 3.7%/4 hours. 19870524 2.6 19870824 4.9 19880104 4.2 Complicated series of decreases into, rapid FD: 4.8%/2 hours. 19880220 5.1 Classic FD; hourly, 8.5%; to = 2.3 days; full recovery. 19880720 2.5 Sudden commencement (SC) about 04 UT on 21 July. 19880824 4.2 Classic FD; 4.4%/5 hours; SC about 10 UT 25 August. 19881009 3.7 Seen in Mt. Washington and Durham hourly data. 19881217 4.7 Hourly, 6.9%/16 hours = 0.4%/hour. 19890104 5.5 Fast FD, <3 hours. 19890211 4.4 Slow FD. 19890312 15.5 Classic FD; hourly 17.1% in two steps. 19890326 3.8 Classic FD; 4.4%/2 hours. 19890809 3.7 Classic FD, 4.45%/2 hours. 19890814 5.5 19890819 4 Small FD during large anisotropies. 19890828 4.9 Fast FD, <2 hours. 19890904 7.2 Slow FD, duration > 2 days. 19890906 4.2 A part of slow FD on 4 September. 19890918 4.2 Slow FD. 19891020 13 Slow FD following large GLE. 19891117 4.2 19891128 16 Classic two step FD. 19900318 6.6 19900407 7.7 19900517 3.9 19910130 3.5 19910312 4.8 19910324 23.5 19910424 6.6 19910528 7.5 19910604 4 19910611 11.2 19910630 7.4 19910708 5.1 19910818 5.1 19911027 10.7 19911031 6 19911107 5.5 19920225 7 19920509 5.6 19920908 4.5 19921031 3.5 19930219 4.8 19931022 4.9 19940220 3.4 19940416 5 19940617 3 19951016 3.7 1996