The Earths Magnetosphere The Earths magnetic field The

The Earth’s Magnetosphere The Earth’s magnetic field The Magnetosphere Magnetic variation and index

http: //ourworld. compuserve. com/homepages/dp 5/magnet. htm

The South Atlantic Anomaly (SAA) is located within the region between 10 -40°S and between 280 -360°E. USGS figure

台灣的磁場特徵(25. 0 °N, 121. 5°E) Total Intensity (F): 45008. 8 n. T 磁偏角 (D): -3. 879 o 磁傾角 (I): 36. 218 o

Dipole magnetic field θ: co-latitude

USGS figure

Field line equation (I) In spherical coordinate, At tangent point, Combine Earth’s magnetic field,

Field line equation (II) Integral (5. 06), At magnetic equator, Let req=L x RE and for r = RE R REE

運動方程式 (Equation of motion)

Closed model

Open model

Magnetospheric Current System Dayside magnetopause current R 1 and R 2 filed-aligned currents Partial ring current Nightside magnetopause current Cross tail current Ring current

Dayside magnetopause current R 1 and R 2 filed-aligned currents Partial ring current Nightside magnetopause current Cross tail current Ring current

Dayside magnetopause current R 1 and R 2 filed-aligned currents Partial ring current Nightside magnetopause current Cross tail current Ring current

Magnetometer • A magnetometer is a scientific instrument used to measure the strength and/or direction of the magnetic field. Magnetism varies from place to place and differences in Earth's magnetic field can be caused by the differing nature of rocks and the interaction between charged particles from the Sun and the magnetosphere. Magnetometers are a frequent component instrument on spacecraft that explore planets.

Types • Scalar magnetometers measure the total strength of the magnetic field to which they are subjected, and • Vector magnetometers have the capability to measure the component of the magnetic field in a particular direction, relative to the spatial orientation of the device.

Early magnetometers • In 1833, Carl Friedrich Gauss, head of the Geomagnetic Observatory in Göttingen, published a paper on measurement of the Earth's magnetic field. It described a new instrument that Gauss called a "magnometer" (a term which is still occasionally used instead of magnetometer). It consisted of a permanent bar magnet suspended horizontally from a gold fibre. A magnetometer may also be called a gaussmeter.

Modern magnetometers • • Rotating coil magnetometer Hall effect magnetometer Proton precession magnetometer Gradiometer Fluxgate magnetometer Induction magnetometer Caesium vapor magnetometer Spin-exchange relaxation-free (SERF) atomic magnetometers

Rotating coil magnetometer • The magnetic field induces a sine wave in a rotating coil. The amplitude of the signal is proportional to the strength of the field, provided it is uniform, and to the sine of the angle between the rotation axis of the coil and the field lines.

Hall effect magnetometer • The most common magnetic sensing devices are solid-state Hall effect sensors. These sensors produce a voltage proportional to the applied magnetic field and also sense polarity.

Proton precession magnetometer • Proton precession magnetometers, also known as proton magnetometers, measure the resonance frequency of protons (hydrogen nuclei) in the magnetic field to be measured, due to nuclear magnetic resonance (NMR). Because the precession frequency depends only on atomic constants and the strength of the ambient magnetic field, the accuracy of this type of magnetometer is very good.

Gradiometer • Magnetic gradiometers are pairs of magnetometers with their sensors horizontally separated by a fixed distance. The readings are subtracted in order to measure the difference between the sensed magnetic fields, which measures the field gradients caused by magnetic anomalies. This is one way of compensating both the variability in time of the Earth's magnetic field and for other sources of electromagnetic interference, allowing more sensitive detection of anomalies.

Fluxgate magnetometer • A fluxgate magnetometer consists of a small, magnetically susceptible, core wrapped by two coils of wire. An alternating electrical current is passed through one coil, driving the core through an alternating cycle of magnetic saturation. This constantly changing field induces an electrical current in the second coil, and this output current is measured by a detector.

Caesium vapor magnetometer • A basic example of the workings of a magnetometer may be given by discussing the common optically pumped caesium vapor magnetometer which is a highly sensitive (300 f. T/Hz 0. 5) and accurate device used in a wide range of applications.

Spin-exchange relaxation-free (SERF) atomic magnetometers • At sufficiently high atomic density, extremely high sensitivity can be achieved. Spin-exchange-relaxationfree atomic magnetometers containing potassium, caesium vapor operate similarly to the caesium magnetometers described above yet can reach sensitivities lower than 1 f. T/Hz 0. 5. • The SERF magnetometers only operate in small magnetic fields. The Earth's field is about 50µT. SERF magnetometers operate in fields less than 0. 5µT.

Geomagnetic pulsations, i. e. , ultra-low-frequency (ULF) waves cover roughly the frequency range from 1 m. Hz to 1 Hz, i. e. , from the lowest the magnetospheric cavity can support up to the various ion gyrofrequencies. Pulsation frequency is considered to be "ultra" low when it is lower than the natural frequencies of the plasma, like plasma frequency and the ion gyrofrequency. Geomagnetic pulsations were first observed in the ground-based measurements of the 1859 great auroraevents (Stewart, 1861). Typical classification scheme for the ULF waves is according to the type (c=continuous, i=irregular) and period of the pulsation (Jacobs et al. , 1964): In addition, pulsations called Ps 6 have been related with omega bands (any others? ). Pulsations are studied with in situ observations in space of both magnetic and electric fields, and with ground-based magnetometers. In order to study the generation mechanisms of these waves, several points should be studied, including • frequency characteristics, incl. harmonic structures • spatial distribution, incl. possible propagation of the waves • polarization characteristics • correlation with IMF/solar wind parameters • correlation with geomagnetic activity, e. g. , phases of storms and substorms • correlation with in situ particle data On ground, an important additional data comes from the optical measurements of auroras. Pc 1 Pc 2 Pc 3 Pc 4 Pc 5 Pi 1 Pi 2 T [s[ 0. 2 -5 5 -10 10 -45 45 -150 150 -600 1 -40 40 -150 f 0. 2 -5 Hz 0. 1 -0. 2 Hz 22 -100 m. Hz 7 -22 m. Hz 2 -7 m. Hz 0. 025 -1 Hz 2 -25 m. Hz

magnetic index 地磁指數 • • K index Kp index, A index AE index Dst index

K index (K 指數) Observatory Geographic Geomagnetic # Code Name Location Active Lat. * Long. * 1 LER Lerwick Scotland 1932 -actual 60° 08' 358° 49' 62. 0° 89. 2° 2 MEA Meanook Canada 1932 -actual 54° 37' 246° 40' 61. 7° 305. 7° 1500 3 SIT Sitka Alaska (US) 1932 -actual 57° 03' 224° 40' 60. 4° 279. 8° 1000 4 ESK Eskdalemuir Scotland 1932 -actual 55° 19' 356° 48' 57. 9° 83. 9° LOV Lovö Sweden 1954 -2004 59° 21' 17° 50' 57. 9° 106. 5° 600 UPS Uppsala Sweden 2004 -actual 59° 54' 17° 21' 58. 5° 106. 4° 600 AGN Agincourt Canada 1932 -1969 43° 47' 280° 44' 54. 1° 350. 5° 600 OTT Ottawa Canada 1969 -actual 45° 24' 284° 27' 55. 8° 355. 0° 750 RSV Rude Skov Denmark 1932 -1984 55° 51' 12° 27' 55. 5° 99. 4° 600 BFE Brorfelde Denmark 1984 -actual 55° 37' 11° 40' 55. 4° 98. 6° 600 ABN Abinger England 1932 -1957 51° 11' 359° 37' 53. 4° 84. 5° 500 HAD Hartland England 1957 -actual 50° 58' 355° 31' 54. 0° 80. 2° 500 WNG Wingst Germany 1938 -actual 53° 45' 9° 04' 54. 1° 95. 1° 500 WIT Witteveen Netherland 1932 -1988 52° 49' 6° 40' 53. 7° 92. 3° 500 NGK Niemegk Germany 1988 -actual 52° 04' 12° 41' 51. 9° 97. 7° 500 CLH Cheltenham USA 1932 -1957 38° 42' 283° 12' 49. 1° 353. 8° 500 FRD Fredericksburg USA 1957 -actual 38° 12' 282° 38' 48. 6° 353. 1° 500 TOO Toolangi Australia 1972 -1981 -37° 32' 145° 28' -45. 6° 223. 0° 500 CNB Canberra Australia 1981 -actual -35° 18' 149° 00' -42. 9° 226. 8° 450 AML Amberley New Zealand 1932 -1978 -43° 09' 172° 43' -46. 9° 254. 1° 500 EYR Eyrewell New Zealand 1978 -actual -43° 25' 172° 21' -47. 2° 253. 8° 500 5 6 7 8 9 10 11 12 13 Long. K=9 (n. T) 1000 • • • 750 • • 13個高緯測站觀測資料 每三個小時觀測一次數值 以各觀測站之歷史觀測為標準化 依據 分0 -9 10個等級 每個等級間格 為類指數型變化 同個K值在不同觀測站有不同之 變化量 http: //www-app 3. gfz-potsdam. de/kp_index/description. html

表 5 -1 K index(K)與地磁變化幅度(R, n. T)之關係(Niemegk, 52° 04’N, 12° 40’E) K= 0 1 2 3 4 5 6 7 8 9 R= 5 10 20 40 70 120 200 330 500

A & ap index K 和 Kp index 都是以類指數型態表示，在數值加總時並不十分方便， 因此透過轉換得將 K 和 Kp index 轉呈線性型態，稱為 A、ap index。 將一日 8個 ap index 作加總，所得之數值即為本日之 Ap index K、A 轉換表 K= A= 0 0 1 3 2 7 3 15 4 27 5 48 6 80 7 140 8 240 9 400 Kp、ap 轉換表 Kp 0 o 0+ 1 - 1+ 1 o 2 - 2 o 2+ 3 - 3 o 3+ 4 - 4 o 4+ ap 0 2 3 4 5 6 7 9 12 15 18 22 27 32 Kp 5 - 5 o 5+ 6 - 6 o 6+ 7 - 7 o 7+ 8 - 8 o 8+ 9 - 9 o ap 39 48 56 67 80 94 111 132 154 179 207 236 300 400 http: //www-app 3. gfz-potsdam. de/kp_index/apdescription. html

AE index (Auroral Electrojet) Ø 位於北極區之13個觀測站 Ø 量測每天地球磁場中的H分量在經度上的變化，用以表示極 區電噴流的大小 Ø 將各個測站所量測到的數值重疊在一起之後，所得到的上邊 界稱之為AU；下邊界則為AL Ø AU代表了東向電噴流的大小，AL代表西向電噴流的大小 Ø AE = AU – AL Ø AO = (AU + AL) /2 IAGA Geographic Coord. Geomagnetic Coord. Observatory Abisko Code ABK Lat. (°N) 68. 36 Long. (°E) 18. 82 Lat. (°N) 66. 04 Long. (°E) 115. 08 Dixon Island DIK 73. 55 80. 57 63. 02 161. 57 Cape Chelyuskin CCS 77. 72 104. 28 66. 26 176. 46 Tixie Bay TIK 71. 58 129. 00 60. 44 191. 41 Cape Wellen CWE 66. 17 190. 17 61. 79 237. 10 Barrow BRW 71. 30 203. 25 68. 54 241. 15 College CMO 64. 87 212. 17 64. 63 256. 52 Yellowknife YKC 62. 40 245. 60 69. 00 292. 80 Fort Churchill FCC 58. 80 265. 90 68. 70 322. 77 Poste-de-la-Baleine PBQ 55. 27 282. 22 66. 58 347. 36 Narsarsuaq (Narssuaq) Leirvogur NAQ LRV 61. 20 64. 18 314. 16 338. 30 71. 21 70. 22 36. 79 71. 04 http: //wdc. kugi. kyoto-u. ac. jp/aedir/ae 2/AETABLE 1. html

Dst index (Disturbance storm time Index)

http: //wdc. kugi. kyoto-u. ac. jp/index. html

Super storms Intense storms Moderate storms Weak storms Dst < -200 n. T < Dst < -100 n. T < Dst < -50 n. T < Dst < -30 n. T

IGRF (International Geomagnetic Reference Field) http: //ccmc. gsfc. nasa. gov/modelweb/models/igrf_vitmo. php