1. Elena Saiz, C. Cid, A. Guerrero, J. Palacios, Y. Cerrato Space Research Group - Space Weather University of Alcalá (Spain) elena.saiz@uah.es

2.  A large depression in the magnetic H-component  It takes place in less than 1 hour  It is a highly local disturbance, showing day (  H 0) asymmetry in longitude  R1 FACs is the current system involved Cid et al. (2015) Abrupt southward turning of IMF Bz (at least 10 nT/min) along with high solar wind pressure ( Saiz et al., to be published soon) a Carrington-like event

3.  Magnetograms of the H- component at five mid-latitude observatories (  45º MLat) spread in longitude from the INTERMAGNET database  We look for both day/night asymmetry and intensity of the disturbance (  H)  Transients: fast forward shocks with B IMF ratio  4 and/or  V sw  250 km/s as probable sources of H-spike triggers  Database: Heliospheric Shock Database by the University of Helsinki  We look for signatures in a few hours after the shock: ICME sheaths Events 18 October 1995 8 June 2000 31 March 2001 28 April 2001 25 September 2001 24 November 2001 26 July 2004 21 January 2005 12 June 2005 12 September 2005 14 December 2006 25 March 2014

4. IP GROUND IP GROUND # Events  Bz  10 nT in 1 min? mid-latitude H-spike? 5 out of 12yes 4 out of 12no 3 out of 12yesno YES A couple of examples 24 November 2001 cause - effect 9 out of 12  75% SH: timing shock 21 January 2005

5.  Hypothesis reinforced with the set of events analysed (75% positive results)  Looking at in longitude, the largest H-spike intensity takes place at the 6-12 MLT sector  Forecasting of these local disturbances becomes a priority Even though interplanetary conditions are met, for developing an H-spike:  is there a minimum time interval  t with negative Bz after a southward Bz turning?  is there a threshold for the negative Bz value?  is there some kind of “coupling” among Bz < 0,  Bz/  t and minimum  t?  or a fluctuating solar wind pressure or a high maintained pressure level? YES NO 31 March 2001 Acknowledgment s. This work has been supported by grants AYA2013-47735-P from the Ministerio de Economía y Competitividad.

6. # Event  Bz  10 nT in 1 min? (6 h after SH H-spike? 18 October 1995 no 8 June 2000 yesno 31 March 2001 yesno 28 April 2001 yesno 25 September 2001 yes Yes? (MMB (6MLT) pero Pacifico por medio; la  H max = es positiva 24 November 2001 yes Yes.  H max = -260; THY, 9MLT 26 July 2004 yes Yes.  H max = -180; MMB, 9MLT 21 January 2005 yes Yes.  Hmax= -170 and -177; FRN and FRD; 9.5 and 12.5 MLT 12 June 2005 no 12 September 2005 nono (visto en conjunto) 14 December 2006 yes Yes.  H max = -106; FRD, 9.75 MLT 25 March 2014 no