Schmucker-Weidelt Lecture Notes, Aarhus, 1975 - MTNet
Schmucker-Weidelt Lecture Notes, Aarhus, 1975 - MTNet Schmucker-Weidelt Lecture Notes, Aarhus, 1975 - MTNet
One of the thin plates represents the ocean and one of its edges is given the shape .of a certain coastline .to be studied. The second plate represents the level of the image currents. The whole arrangement of conductors is placed into a Helmholtz coil in such a way that the vertical strips are parallel to . the. magnetic field. Plates and st~-.ips now form a loop normal to the magnetic flux within the ~elmhoytz coil and thus currents are induced which flow in the "oceanic" plate parallel to the "coastline". In SPITTA's arrangement for th.e study of the coast effect the con- ductors are placed below a horizontal band-current closed by a large vertical loop. The oceanic and continental substructure is represented by a thick metalic plate, the oceans by a thin metalic sheet which partially covers the plate. The thickness of the plate is large in comparison to the skin depth and its width about twice the half-width of the field of the band- current at the level of the plate. The induced current systems form closed loops within plate and sheet and can be assumed to be largely horizontal. By placing one edge of the covering sheet below the 'center of the band-curren-t the coast effect of an ionospheric jet can be studied for any angle between coast and jet. 1,
The ratio of the length-scales model: nature should be in the 6 7 order 1 : 10 or 1 : 10 . In this way current loops of some 1000 km in nature can be reproduced. In SPITTA's' experiment the ratio of length-scales is 1 : 4.10~. A 4 km thick ocean is re- presented by an aluminium sheet of 1 rrn thickness, a highly con- ducting layer in the mantle at 360 km depth'by an aluminum plate 9 cm below the sheet. The width of this plate is 2 m and is equivalent to 8000 km in nature. Model conductors niay be chosen from the following materials: cu - AL - ~b 7 .- 0.5.107 (am)-' Graphite 3.10~ ' 11 (saturated) NaCl solution (concentration of maximum conductivity ) In SPITTA's experiment the conductivity-ratio model: nature is 7 2.10 : 4. Hence; with a ratio of length scales of 1/4 a frequency of 1 kHz in the model corresponds to 1/32.10-~ Hz 'lcph in nature. DOSSO uses graphite to represent the oceans and highly conduc- ting material in the deeper mantle, saturated NaC1-solution to represent the continental surface layers and the poorly conduc- ting portions of crust and uppermost mantle. Since his model frequencies are only slightly higher (1 to 60 kHz),.a one orbder 5 of magnitude pester ratio of length-scales (1:lO 1 has to be used to simulate natural frequencies between 1 cph and 1 cpm. , The lists of available model conductors shows that it is diffi- cult to simulate. conductivity contrasts of 1:10 or 1:100 which are of particular importance in the natural induction process. Only salt solutions of variable concentration could provide a sufficient range in xodel conductivity, but their relatively
- Page 126 and 127: (e.g. X), their realizations by obs
- Page 128 and 129: Observe that the residual, of which
- Page 130 and 131: Example: n = 12 and @ = 95%: 1 n =
- Page 132 and 133: - As a consequence, the real and im
- Page 134 and 135: This relati-on implies .that .the l
- Page 136 and 137: 9. --- Data 5.nterpretatj.on on the
- Page 138 and 139: The "modified apparent - - resistiv
- Page 140 and 141: Exercise Geomagne-tic varj.ations.
- Page 142 and 143: 9.2 Layered Sphere - The sphericity
- Page 144 and 145: The field within the conducting sph
- Page 146 and 147: and An algorithm for the direct pro
- Page 148 and 149: with I - and- a = gn g-n I 1 6-n-1
- Page 150 and 151: with ~ = - T E + as sheet current d
- Page 152 and 153: E~~ T r: j = const. or E T + E a r
- Page 154 and 155: Field equations and boundary condit
- Page 156 and 157: with N (w,y) being the Fourier tran
- Page 158 and 159: is calculated as function of freque
- Page 160 and 161: Both types of anomaly can be explai
- Page 162 and 163: A field line segment with the horiz
- Page 164 and 165: - 160 - below can neither enter nor
- Page 166 and 167: I '. - L.. . . - I . --.> . ~ 4 The
- Page 168 and 169: This law can be used to i-nterpret
- Page 170 and 171: Only in this special case will be j
- Page 172 and 173: anomalous conductivity oat OP the a
- Page 174 and 175: the product WUL' constant with L de
- Page 178 and 179: low conductivity requires the use o
- Page 180 and 181: Other derivable properties of mantl
- Page 182: 11. References for general reading
The ratio of the length-scales model: nature should be in the<br />
6 7<br />
order 1 : 10 or 1 : 10 . In this way current loops of some<br />
1000 km in nature can be reproduced. In SPITTA's' experiment the<br />
ratio of length-scales is 1 : 4.10~. A 4 km thick ocean is re-<br />
presented by an aluminium sheet of 1 rrn thickness, a highly con-<br />
ducting layer in the mantle at 360 km depth'by an aluminum plate<br />
9 cm below the sheet. The width of this plate is 2 m and is<br />
equivalent to 8000 km in nature.<br />
Model conductors niay be chosen from the following materials:<br />
cu - AL - ~b 7 .- 0.5.107 (am)-'<br />
Graphite 3.10~ ' 11<br />
(saturated)<br />
NaCl solution<br />
(concentration of maximum<br />
conductivity )<br />
In SPITTA's experiment the conductivity-ratio model: nature is<br />
7<br />
2.10 : 4. Hence; with a ratio of length scales of 1/4 a<br />
frequency of 1 kHz in the model corresponds to 1/32.10-~ Hz 'lcph<br />
in nature.<br />
DOSSO uses graphite to represent the oceans and highly conduc-<br />
ting material in the deeper mantle, saturated NaC1-solution to<br />
represent the continental surface layers and the poorly conduc-<br />
ting portions of crust and uppermost mantle. Since his model<br />
frequencies are only slightly higher (1 to 60 kHz),.a one orbder<br />
5<br />
of magnitude pester ratio of length-scales (1:lO 1 has to be<br />
used to simulate natural frequencies between 1 cph and 1 cpm.<br />
,<br />
The lists of available model conductors shows that it is diffi-<br />
cult to simulate. conductivity contrasts of 1:10 or 1:100 which<br />
are of particular importance in the natural induction process.<br />
Only salt solutions of variable concentration could provide a<br />
sufficient range in xodel conductivity, but their relatively
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