occurrence of a traveling ionispheric disturbance, observed by the Arecibo rad.al.in Puerto Rico, rnoving fron sc,itli-er,st i,. nolth-+iesi, riuriilg tl:rr: eariy mornjr,g of 22 Septenber. But, on the grounds that up until the sighting of this disturbance, there had been only linited observation on which to base an estimate of tlle frequency of natura] occurrence of such a disturbance, the presence of a tropical storm near Arecibo {hich could have generated an ionispheric disturbance " ancl uncertainty about the velocity - and thus the origin - of the signal, the ad hoc n.ral 1.A1F.+a4 fhic di c+.urbance aS evidence.^/35/\02English Annex Page 35 75. sinil-arly, the requests of the secretary-General and the special cornrnitteeAgainst Apartheid ilurediately follow"ing the announcenent of the 22 September eventthat Member states provid.e any infornation that they night have about that eventalso failed to turn up corroborative evidence. of the states that replied to theseparticular inquiries " 12/ none had any such information. other infornation,includ.ing the report of the ad hoc pane1, vas later suppliett to thesecretsry-GeneTal by the unitett states while inconclusive replies also werereceived from llew Zealand and. the United Kingd.on. 76. Nevertheless, some questions stilr- remain, partieular\r since the detair,sregarding the recorded signals and. the nonitoring equipment, Anerican or othe",have not been fully disclosed. According to sone experts vith experience innuclear-Feapon testing, there are conditions uniler which a very l-ov yielit nuclearexplosion could result in no observable raclio.-actite fall-.-out after ll+ hours. If such a d.evice were detonat ed. at a 1ow altitud.e, for exaup]e, its fatl-out rnight not be ca"ri.ed into the higher atnosphere and coulcl quickly cone dovn to earth .eith
**Analysis**
The text appears to be discussing a scientific phenomenon, specifically the occurrence of a traveling ionispheric disturbance and its potential connection to a nuclear explosion. The text mentions the involvement of international organizations and countries, and the lack of conclusive evidence. The tone is technical and scientific, with no mention of economic, social, or cultural aspects.

**Category**
Science and technology, International trade