Try this: www.igpp.ucla.edu/public/ekassie/Chapter_3_Final.pdf

Hello Ibanga,

Please click on this link http://wdc.kugi.kyoto-u.ac.jp/wdc/Sec3.html to obtain the 

Geomagntic indices , Kp and Ap.

The delay experienced by the GPS signals is directly proportional to the TEC. Moreover, this delay is dispersive, i.e. frequency dependent. So, the range measured using a signal of frequency f is Rm  = Rg + 40.3 TEC/f^2. where Rm and Rg are the measured and geometric ranges respectively. Now, if you have two simultaneous measurements from the same GPs satellite using two frequencies, say f1 and f2, and difference them, the diiferential range becomes dR = 40.3 TEC [ (1/f1^2) - (1/f2^2)]. As you know dR from measurements and f1 and f2 are your known frequencies, TEC can be easily determined. Hope this helps. For, further clarification you may refer to my book: Understanding Satellite Navigation at 

 http://store.elsevier.com/Understanding-Satellite-Navigation/Rajat-Acharya/isbn-9780127999494/

The Kp and Ap magnetic indices are the same measurement of geomagnetic activity  

the Kp is given on a scale from 0 to 9 and the Ap index is given in nan teslas

The Kp and Ap indices are not depending on a given place they are a measure of the global magnetic activity

You can find  these indices on the website: International service of Geomagnetic Indices

ISGI (type on google International Service of Geomagnetic Indices). On  this website you can find all other magnetic indices as Dst, Au and AL etc...