M.J. Rivas (rivasmmj@inta.es) [1,2], C. Cid [1] RELATIONSHIP BETWEEN THE INTENSITY OF X-RAY FLARES AND THEIR EFFECTS IN THE HORIZONTAL COMPONENT OF THE GEOMAGNETIC FIELD M.J. Rivas (rivasmmj@inta.es) [1,2], C. Cid [1] [1] Universidad de Alcalá, Spain; [2] Instituto Nacional de Técnica Aeroespacial (INTA), Spain

M.J. Rivas (rivasmmj@inta.es) [1,2], C. Cid [1] RELATIONSHIP BETWEEN THE INTENSITY OF X-RAY FLARES AND THEIR EFFECTS IN THE HORIZONTAL COMPONENT OF THE GEOMAGNETIC FIELD M.J. Rivas (rivasmmj@inta.es) [1,2], C. Cid [1] [1] Universidad de Alcalá, Spain; [2] Instituto Nacional de Técnica Aeroespacial (INTA), Spain PROCEDURE RESULTS CONCLUSIONS BIBLIOGRAPHY: Cliver and Dietrich. The 1859 space weather event revisited: limits of extreme activity (2013); Curto, Amory-Mazaudier, Torta and Menvielle. Solar flare effects at Ebre: Regular and reverse solar flare effects, statistical analysis (1953 to 1985), a global case study and a model of elliptical ionospheric currents (1994); Rastogi, Pathan, Rao, Sastry and Sastri. Solar flare effects on the geomagnetic elements during normal and counter electrojet periods (1999); Reddy. The Equatorial Electrojet (1989); Sastri and Murthy. On the relationships between SFE (crochet) and solar X-ray and microwave bursts (1974); Villante and Regi. Solar flare effect preceding Halloween storm (28 October 2003): Results of a worldwide analysis (2008); www.intermagnet.org; http://www.ngdc.noaa.gov/nndc/struts/results?t=102827&s=1&d=8,2,9; ]; http://www.esrl.noaa.gov/gmd/grad/solcalc/. INTRODUCTION ABSTRACT: Intense solar flares produce sometimes a disturbance on the ground magnetic field labelled as magnetic-crochet or solar flare effect (SFE). The intensity of the flare has been suggested to be related to the size of the SFE, but no relationship between both magnitudes has been established up to date. In this communication we present the results from a statistical analysis along one solar cycle involving some parameters related to the intensity of the X-flares (integral flux and peak flux) and the size of the SFE at different magnetic observatories from the INTERMAGNET data network. The position of the magnetic observatory relative to the Subsolar point has also been considered in this study. WHAT A SFE OR CROCHET IS? NO FLARE CONDITIONS: Ionospheric currents in E-region produced by dynamo effect (conductor moving inside the geomagnetic field). FLARE CONDITIONS: Distortion of ionospheric currents in E-region due to enhanced UV radiation. Ionospheric D-region becomes ionised due to enhanced X radiation; currents appear in D-region. Crochets or SFEs detected in magnetic observatories on Earth about 8 minutes after the flare occurs in the Sun. UV & X (8 min aprox.) CROCHET OBJECTIVE: A relationship between the intensity of the flare and the height of the crochet produced is searched. Intensity (expressed as integral flux or peak flux) will be obtained from GOES data for a whole solar cycle (2004 – 2014). The second parameter (absolute value of the difference between H at the beginning and the peak of the crochet) will be obtained from measurements in INTERMAGNET magnetic observatories. 34 X-class flares will be considered.

M.J. Rivas (rivasmmj@inta.es) [1,2], C. Cid [1] RELATIONSHIP BETWEEN THE INTENSITY OF X-RAY FLARES AND THEIR EFFECTS IN THE HORIZONTAL COMPONENT OF THE GEOMAGNETIC FIELD M.J. Rivas (rivasmmj@inta.es) [1,2], C. Cid [1] [1] Universidad de Alcalá, Spain; [2] Instituto Nacional de Técnica Aeroespacial (INTA), Spain RESULTS CONCLUSIONS BIBLIOGRAPHY: Cliver and Dietrich. The 1859 space weather event revisited: limits of extreme activity (2013); Curto, Amory-Mazaudier, Torta and Menvielle. Solar flare effects at Ebre: Regular and reverse solar flare effects, statistical analysis (1953 to 1985), a global case study and a model of elliptical ionospheric currents (1994); Rastogi, Pathan, Rao, Sastry and Sastri. Solar flare effects on the geomagnetic elements during normal and counter electrojet periods (1999); Reddy. The Equatorial Electrojet (1989); Sastri and Murthy. On the relationships between SFE (crochet) and solar X-ray and microwave bursts (1974); Villante and Regi. Solar flare effect preceding Halloween storm (28 October 2003): Results of a worldwide analysis (2008); www.intermagnet.org; http://www.ngdc.noaa.gov/nndc/struts/results?t=102827&s=1&d=8,2,9; ]; http://www.esrl.noaa.gov/gmd/grad/solcalc/. INTRODUCTION PROCEDURE PROCEDURE 1: Determination of the crochet height value at the Sub-Solar Point (SSP) Crochet height is expected to have its maximum value at the SSP [Villante 2008], and to decrease as the distance from the observatory to the SSP increases. The SSP is the point where an observer can see the Sun in the zenith when the flare electromagnetic radiation reaches the Earth. Crochet height at the SSP is the optimum value for being related to the intensity of the flare. However, there is a small probability of finding an observatory situated exactly at the SSP when a flare occurs. So, the crochet height at the SSP must be extrapolated from measurements at other observatories. As a first step, a relationship between the height of the crochet produced by a flare and the distance from the magnetic observatory to the flare SSP is searched. If this relationship is found and valid in all the cases, we will be able to calculate the crochet height at the SSP for all the flares to be analysed. For three flares, measurements in observatories located no farther than 40 degrees North, South, East or West from the SSP are taken, so that the relationship between the crochet height and the distance of the observatory to the SSP can be established. PROCEDURE 2: Statistical approach In this case, instead of searching for the crochet height value at the SSP, a statistical approach is used. The approach consists in considering all the observatories situated no farther tan 20 degrees North, South, East or West from the SSP for every flare to be analysed. The crochet height to be considered for the searched relationship between such height and the intensity of the flare will be the medium value of all the crochet heights measured in the mentioned observatories. Some INTERMAGNET observatories and a selection for statistical approach

RELATIONSHIP BETWEEN THE INTENSITY OF X-RAY FLARES AND THEIR EFFECTS IN THE HORIZONTAL COMPONENT OF THE GEOMAGNETIC FIELD M.J. Rivas (rivasmmj@inta.es) [1,2], C. Cid [1] [1] Universidad de Alcalá, Spain; [2] Instituto Nacional de Técnica Aeroespacial (INTA), Spain PROCEDURE CONCLUSIONS BIBLIOGRAPHY: Cliver and Dietrich. The 1859 space weather event revisited: limits of extreme activity (2013); Curto, Amory-Mazaudier, Torta and Menvielle. Solar flare effects at Ebre: Regular and reverse solar flare effects, statistical analysis (1953 to 1985), a global case study and a model of elliptical ionospheric currents (1994); Rastogi, Pathan, Rao, Sastry and Sastri. Solar flare effects on the geomagnetic elements during normal and counter electrojet periods (1999); Reddy. The Equatorial Electrojet (1989); Sastri and Murthy. On the relationships between SFE (crochet) and solar X-ray and microwave bursts (1974); Villante and Regi. Solar flare effect preceding Halloween storm (28 October 2003): Results of a worldwide analysis (2008); www.intermagnet.org; http://www.ngdc.noaa.gov/nndc/struts/results?t=102827&s=1&d=8,2,9; ]; http://www.esrl.noaa.gov/gmd/grad/solcalc/. INTRODUCTION RESULTS RESULTS FOR PROCEDURE 1: After analysing three flares, no relation was found between the height of the crochet produced by a flare and the distance from the magnetic observatory to the flare SSP. Observatories: Distance to SSP increasing HUA RESULTS FOR PROCEDURE 2: Where: F = integral flux of the flare P = maximum flux of the flare (peak flux) A = medium value of the heights of the crochets produced by a flare, measured in observatories located at a distance of the SSP no longer than 20 degrees North, South, East and West

M.J. Rivas (rivasmmj@inta.es) [1,2], C. Cid [1] RELATIONSHIP BETWEEN THE INTENSITY OF X-RAY FLARES AND THEIR EFFECTS IN THE HORIZONTAL COMPONENT OF THE GEOMAGNETIC FIELD M.J. Rivas (rivasmmj@inta.es) [1,2], C. Cid [1] [1] Universidad de Alcalá, Spain; [2] Instituto Nacional de Técnica Aeroespacial (INTA), Spain PROCEDURE RESULTS BIBLIOGRAPHY: Cliver and Dietrich. The 1859 space weather event revisited: limits of extreme activity (2013); Curto, Amory-Mazaudier, Torta and Menvielle. Solar flare effects at Ebre: Regular and reverse solar flare effects, statistical analysis (1953 to 1985), a global case study and a model of elliptical ionospheric currents (1994); Rastogi, Pathan, Rao, Sastry and Sastri. Solar flare effects on the geomagnetic elements during normal and counter electrojet periods (1999); Reddy. The Equatorial Electrojet (1989); Sastri and Murthy. On the relationships between SFE (crochet) and solar X-ray and microwave bursts (1974); Villante and Regi. Solar flare effect preceding Halloween storm (28 October 2003): Results of a worldwide analysis (2008); www.intermagnet.org; http://www.ngdc.noaa.gov/nndc/struts/results?t=102827&s=1&d=8,2,9; ]; http://www.esrl.noaa.gov/gmd/grad/solcalc/. INTRODUCTION CONCLUSIONS CONCLUSIONS: The height of the crochet produced by a flare can’t be calculated from measurements of crochets produced by the same flare in observatories located near the SSP. Is really the crochet height maximum at the SSP??? A mathematical relation between A (medium value of the crochet heights) and F (integral flux of the flare) or between A and P (peak flux of the flare) hasn’t been found. However , A increases as F increases and, for high F values A seems not to continue increasing. It could be due to a saturation in the ionisation of the ionosphere; when the ionisation stops increasing, so does the height of the crochets. However, a new study would be necessary which includes more high values for F parameter to confirm this consideration. Nothing similar happens with A and P, parameters which seem not to have any relationship. So, detection and characterization of crochets does not seems to be accurate enough to be used, at the moment, for detection and characterization of solar flares. Short flares (tens of minutes) have been more easily identified than those longer than 1 hour. So the measurements of the crochet heights in the first case are more accurate. A new study could be carried out with just short flares. For every X-flare considered, crochets were identified in most of the observatories located near de SSP. With these data we could conclude that probably X-class flares always produce crochets but, in some cases, local disturbances of the magnetic field make very difficult to extract SFE from noise.