Z-component Of Interplanetary Magnetic Field Research Articles

Thermospheric NO Cooling during an Unusual Geomagnetic Storm of 21–22 January 2005: A Comparative Study between TIMED/SABER Measurements and TIEGCM Simulations

The geomagnetic storm is the manifestation of the solar wind–magnetosphere interaction. It deposits huge amount of the solar energy into the magnetosphere–ionosphere–thermosphere (MIT) system. This energy creates global perturbations in the chemistry, dynamics, and energetics of the MIT system. The high latitude energy deposition results in the Joule and particle heating that subsequently increases the thermospheric temperature. The thermospheric temperature is effectively regulated by the process of thermospheric cooling emission by nitric oxide via 5.3 µm. A peculiar, intense geomagnetic storm (Dst = −105 nT) occurred during 21–22 January 2005, where the main phase developed during the northward orientation of the z-component of interplanetary magnetic field. We utilized the nitric oxide 5.3 µm infrared emission from the NCAR’s Thermosphere–Ionosphere–Electrodynamics General Circulation Model (TIEGCM) simulation and the Sounding of Atmosphere using Broadband Emission Radiometry (SABER) onboard the thermosphere–ionosphere–mesosphere energetic and dynamics satellite to investigate its response to this anomalous geomagnetic storm. We compared the model results with the observations on both the local and global scales. It is observed that the model results agree very well with the observations during quiet times. However, the model severely underestimates the cooling emission by one-fourth of the observations, although it predicts an enhancement in the thermospheric temperature and densities of atomic oxygen and nitric oxide during the geomagnetic storm.

Aspects related to variability of radiative cooling by NO in lower thermosphere, TEC and O/N2 correlation, and diffusion of NO into mesosphere during the Halloween storms

Nitric Oxide is a very important trace species which plays a significant role acting as a natural thermostat in Earth’s thermosphere during strong geomagnetic activity. In this paper, we present various aspects related to the variation in the NO Infrared radiative flux (IRF) exiting the thermosphere by utilizing the TIMED/SABER (Thermosphere Ionosphere Mesosphere Energetics and Dynamics/ Sounding of the Atmosphere using Broadband Emission Radiometry) observational data during the Halloween storm which occurred in late October 2003. The Halloween storm comprised of three intense-geomagnetic storms. The variability of NO infrared flux during these storm events and its connection to the strength of the geomagnetic storms were found to be different in contrast to similar super storms. The connection between the quantum of energy outflux from the upper atmosphere into space in terms of NO IRF and the duration of storms is established. The NO radiative cooling, and the closely correlated depletion in O/N2 ratio are controlled by the Joule heating intensity (proxied by AE-index). The collisional excitation rate of NO, calculated using the modelled datasets of WACCM-X (Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension), correlates well with the observed pattern of radiative emission by NO. Observational datasets from TIMED/GUVI (Global Ultra-Violet Imager) and MIT Haystack observatory madrigal GNSS (Global navigation satellite system) total electron content (TEC) database shows that the TEC and O/N2 enhancement in low-mid northern hemispheric latitudes are mainly controlled by the z-component of Interplanetary magnetic field (IMF-Bz). The penetration of eastward electric field during the storm events is found to be responsible for the overall enhancement of TEC. The contribution of enhanced day-side TEC in observed variation of O/N2 ratio by GUVI is also reported. It is also seen that during substorms related events the night-time polar region experiences more cooling due to NO than the daytime polar region. The connections between the mid- and low-latitude enhancement in NO IRF with the propagation of LSTIDs (Large-scale traveling ionospheric disturbances) in combination with the O/N2 variability, and the altitudinal variation in NO flux with the progression of the storm is also investigated. This study presents the evidence on the role of diffusion processes in the large scale enhancement of NO in the mesospheric altitudes.

Interplanetary magnetic field and solar rotation

This article presents analysis of interplanetary magnetic field (IMF) B measured at the L1 point outside the geo-magnetosphere. The autocorrelation of daily values of the Bx and By component of the IMF reveal clear solar rotational modulation. The Bz (z-component of IMF) mostly do not show any such modulation. The sidereal solar rotation period are estimated from the IMF data of ACE satellite during 1998–2009. These estimates vary from 24.1 to 25.8 days with a mean value ∼25 days. These annual values are compared with the estimates by the similar method using solar disk integrated radio flux at 2.8GHz and solar images. The images used are (1) Radio images at 17GHz and (2) X-ray images by Yohkoh satellite. The comparison reveals evidence that the IMF seems to mostly originate from the low latitude regions in the solar atmosphere rather than from higher latitudes. The results contradict the existing solar magnetic field model.

Large enhancements in low latitude total electron content during 15 May 2005 geomagnetic storm in Indian zone

Abstract. Results pertaining to the response of the equatorial and low latitude ionosphere to a major geomagnetic storm that occurred on 15 May 2005 are presented. These results are also the first from the Indian zone in terms of (i) GPS derived total electron content (TEC) variations following the storm (ii) Local low latitude electrodynamics response to penetration of high latitude convection electric field (iii) effect of storm induced traveling atmospheric disturbances (TAD's) on GPS-TEC in equatorial ionization anomaly (EIA) zone. Data set comprising of ionospheric TEC obtained from GPS measurements, ionograms from an EIA zone station, New Delhi (Geog. Lat. 28.42° N, Geog. Long. 77.21° E), ground based magnetometers in equatorial and low latitude stations and solar wind data obtained from Advanced Composition Explorer (ACE) has been used in the present study. GPS receivers located at Udaipur (Geog. Lat. 24.73° N, Geog. Long. 73.73° E) and Hyderabad (Geog. Lat. 17.33° N, Geog. Long. 78.47° E) have been used for wider spatial coverage in the Indian zone. Storm induced features in vertical TEC (VTEC) have been obtained comparing them with the mean VTEC of quiet days. Variations in solar wind parameters, as obtained from ACE and in the SYM-H index, indicate that the storm commenced on 15 May 2005 at 02:39 UT. The main phase of the storm commenced at 06:00 UT on 15 May with a sudden southward turning of the Z-component of interplanetary magnetic field (IMF-Bz) and subsequent decrease in SYM-H index. The dawn-to-dusk convection electric field of high latitude origin penetrated to low and equatorial latitudes simultaneously as corroborated by the magnetometer data from the Indian zone. Subsequent northward turning of the IMF-Bz, and the penetration of the dusk-to-dawn electric field over the dip equator is also discernible. Response of the low latitude ionosphere to this storm may be characterized in terms of (i) enhanced background level of VTEC as compared to the mean VTEC, (ii) peaks in VTEC and foF2 within two hours of prompt penetration of electric field and (iii) wave-like modulations in VTEC and sudden enhancement in hmF2 within 4–5 h in to the storm. These features have been explained in terms of the modified fountain effect, local low latitude electrodynamic response to penetration electric field and the TIDs, respectively. The study reveals a strong positive ionospheric storm in the Indian zone on 15 May 2005. Consequences of such major ionospheric storms on the systems that use satellite based navigation solutions in low latitude, are also discussed.

Relationships for predicting magnetic cloud-related geomagnetic storm intensity

Studying geomagnetic storm activity during 135 interplanetary magnetic cloud periods from 1965 to 1998, Wu and Lepping (J. Geophys. Res. 107 (2002b) 1346) found that the storm Dst index correlated well with both the interplanetary magnetic field z-component ( B z ) and the “rectified” electric field VB s but did not correlate well with solar wind speed. It is shown that the role of magnetic cloud speed in predicting storm intensity is a minor one. It also was found that the correlation coefficient for Dst vs. B z increases dramatically when the solar wind speed exceeds 600 km/s. This implies that solar wind speed is also important indirectly for predicting the storm intensity when using B z (or VB s ) as a direct predictor. Using the same data set of 135 magnetic cloud-associated storms, two Dst prediction-relationships were developed: one is velocity independent and the other is velocity dependent. In this study, (i) both Dst prediction-relationships will be presented and (ii) some recent storm events will be presented and discussed by (as examples) using both Dst prediction-relationships. The results of this study also show: (1) The intensity of a magnetic storm which is associated with a magnetic cloud is predictable. (2) The prediction relationships for storm intensity, Dst min are: Dst min = 0.83 + 7.85 × Bz min and Dst min = - 16.48 – 12.89 × ( VB s ) max . (3) The velocity dependence of the Dst min prediction relationship will improve the accuracy for a Bz -base prediction result. (4) For the VB s max -based prediction relationship, the prediction accuracy of Dst min becomes worse when a velocity-dependent prediction relationship is used.

The relativistic electron response in the outer radiation belt during magnetic storms

Abstract. The relativistic electron response in the outer radiation belt during magnetic storms has been studied in relation to solar wind and geomagnetic parameters during the first six months of 1995, a period in which there were a number of recurrent fast solar wind streams. The relativistic electron population was measured by instruments on board the two microsatellites, STRV-1a and STRV-1b, which traversed the radiation belt four times per day from L ~ 1 out to L ~ 7 on highly elliptical, near-equatorial orbits. Variations in the E > 750 keV and E > 1 MeV electrons during the main phase and recovery phase of 17 magnetic storms have been compared with the solar wind speed, interplanetary magnetic field z-component, Bz , the solar wind dynamic pressure and Dst *. Three different types of electron responses are identified, with outcomes that strongly depend on the solar wind speed and interplanetary magnetic field orientation during the magnetic storm recovery phase. Observations also confirm that the L-shell, at which the peak enhancement in the electron count rate occurs has a dependence on Dst *.Key words. Magnetospheric physics (energetic particles, trapped; storms and substorms) – Space plasma physics (charged particle motion and accelerations)

Sandpile model analogy of the magnetosphere-ionosphere substorm activity

Observational studies of magnetospheric activity suggest that magnetosphere-ionosphere coupling plays a critical role in the physical processes leading up to substorm onset. The sandpile cell model as an analogy of the dynamic magnetosphere-ionosphere system related with the substorm activity is presented. Dynamics of the cell model for constant input parameters and for driving by z-component of Interplanetary Magnetic Field (IMF Bz) is discussed. It was found that the model demonstrates some features observed in the magnetosphere-ionosphere system (Lui et al., 2000).