Geomagnetic field measurements at Hong Kong

by Neighbour, Michael Robert

Abstract of thesis ent1tled "Geomagnetic Field Measurements at Hong Kong" .ubmttted by M.R. Netghbour for the degree of M.Ph11 at tile UnJ.veratty of Hong Kong in December 1971.

Since 1884 three widely .eparated sltea bave been \lIed for regular geomagnetio observatJona in Hong Kong.

The pre.ent ob..-vatory ha. been e.tabUlhed at Tate', CaJm end equipped with a La COUl' normal magnetograph; ablOlute determinations are made u8in9 a Quartz Horizontal Magnetometer (Q.M.H.) and a Magnetic Zero Balance (B.M.Z.). After the .at1sfaotoly eatabUshment of the equipment at Tate'. Cairn and the routine producUon of magnetograma, a s.le. of m urementa at Tate', Cairn and at Au Tau, the pre-war atte, wa. und.-taken. From the mea.urementa at both .ite." geomagnetic .lte dlfferenoes have been establ1ahed.

Theae difference" Au Tau - Tates Can. yield valu  of -18l.6'Y 1n the H0C'1zontal oomponent, -221.4 y in the vertical component and 6.904' in the dec11naUon. U.ing these value. the present

valuea obtained at Tate's Cairn could be plotted with the previous

data which were obtained at Hong Kono. Theae previoUS data were thoroughly researched and made seU constatent with the Au Tau results. The average rate. of oban;e between 1939, the last full year of geoma9lletJ.c measurements, and 1971  +16.7y lye . in Hor1zontal component, i9.5 r lyear 1ft vertical oomponent, and 1.1' weatlyeer in decJJnaUon. The  value. show reasonable agreement with rate. pred1cted from other evidence.

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Statement of Author'. Contribution.

Prior to the eatabllshment of the Tates Caim Geomagnetic Ob.ervatory the author undertook an extensive of the literature for geomagnet1c mealurements mede In Hong Xong. Thi. search revealed that prior to 1884 only. small number of results

had been taken, the  belDg 01 dubiousva1ue. Measurements taken between 1884 and 1939 were carried out by the Royal Observatory, the site of oblervaUon being ahaRged on two oecaaJone. Apart

from stte correct.IDns th  wen numerou. other CIOI'I'eOUona revea1ecl In thl. data search. The CX)I'I'8atJonl were brou9ht fog-8th. aDd the data oonected to brln9 1t into line with the 1aat aite used by

the Royal ObaervatDry at Au Tau, and yearly valuea;of the total

foroe and Its component value. for 1884 to 1939 obta.tned. A further data search was made for reaults between 1939 arttS la11 th1a revealed 11ttle. a1pUteut lnformatJon.

'1'0 obtain reliable lDformatioft on the value of the 9eom89MUc field In 1971, it was fir.t  nt1a1 that the Pft>posed geomagnetic ob.ervatory was  tabl18hed at Tat.8 Caitft. 'lh. ob.ervatory wae equipped with La COUl' vlliometer'8 wh1ah Vi" a (X)nttnuous photographic record of the geomagnetic f1e1cl. The tnWa1 adJu8tments and  tUng up of the La COUl' varlomet was jointly done by the author and Dr. D.G. Rivera. The final adJustmeata and  tabU.hment of the various

ooutantl 1rlvolved in the La COUI' var10meten was canied out by

the author .s well  u1muth m81'ks requJl'ed for the absolute

inatrum  The routine d\ang1ng and developing of recorda and

tald.no acale value determ1natJona were undertaken by the Royal ObservatorY after the sauafactolY setting up of the equipment and

trial period.

I

The routine productJon of ma9ftetograms (ma;net1c records) meant that accurate measurements of lDter-slte d1fferenoes could be made between Au Tau (pre-wer lite) and rates Can (present site).

The inter-slte comparison. undertaken by the author oonabted of

taking absolute measurements at both site. and relating these meaaurementa to a fJxed. ba.e JJne on the magnetograms. The ba  Un  derived from each site were then compand.

A recal1bratJon of the Quartz HoriBontal Magnetometers(Q. H. M.) I the ablOlute instruments for measuring the Horizontal component and

the Declination of the geomagnetic fl8ld was found to be necessary

and was undertaken by the author.

With the embl1ahment of lite d1ffereaoel and recal1bratton I me.sunmenta at Tate. Caw cx>uJd be compared with tho.e taken at Au Tau and secular variation curve. drawn for Hong Kong. The  curve. were then compared with predicted value. for the secular vartalion.