We report observations of a steady 20 year decline of solar photospheric fields at latitudes ≥45° starting from ∼1995. This prolonged and continuing decline, combined with the fact that cycle 24 is already past its peak, implies that magnetic fields are likely to continue to decline until ∼2020, the expected minimum of the ongoing solar cycle 24. In addition, interplanetary scintillation observations of the inner heliosphere for the period 1983–2013 and in the distance range 0.2–0.8 AU have also shown a similar and steady decline in solar wind microturbulence levels, in sync with the declining photospheric fields. Using the correlation between the polar field and heliospheric magnetic field (HMF) at solar minimum, we have estimated the value of the HMF in 2020 to be 3.9 (±0.6) nT and a floor value of the HMF of ∼3.2 (±0.4) nT. Given this floor value for the HMF, our analysis suggests that the estimated peak sunspot number for solar cycle 25 is likely to be 62 (±12).

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[1] Observations of signatures of the large-scale wave structure (LSWS) and subsequent development of equatorial spread F (ESF) by using data from a newly installed digital ionosonde at Trivandrum (8.5 N; 77 E; 0.5 N magnetic dip latitude) are presented. The LSWS signatures are observed using the ionograms with echo directions. The 'satellite' traces are shown as echoes from oblique directions, when an upwelling (associated with LSWS) is not directly over the ionosonde location. When an upwelling is centered overhead, and the radius of curvature of the isodensity contours matches the height of reflection, signals from various directions can add in phase to enhance the ionospheric reflection coefficient, and produce another ionogram signature, referred to as multireflected echoes (MREs). It is also shown that the generation of ESF is related to the presence of LSWS. The skymaps also show the presence of small-scale wave structures in the bottomside F region. The investigation also indicates that the range spread F (RSF) occurs because of the reflections from the embedded smaller-scale structures within the large-scale upwelling.

[1] The moderate geomagnetic storm (minimum SYM-H = −89 nT) that occurred during the period from 21 to 25 July 2009 is anomalous because the storm main phase developed during northward interplanetary magnetic field (IMF). A reduction (for ∼4 h) in the daytime E region westward drift (eastward electric field) over the magnetic equatorial location of Trivandrum (8.5°N, 77°E; dip latitude ∼0.5°N) in India is observed during the storm main phase. This reduction in the drift is also indicated by the disappearance of the equatorial sporadic E region (E sq ) echoes on the ionograms. It is suggested that an additional westward prompt penetration electric field characterized by the northward IMF B z is superposed on the ionosphere during the storm main phase which contributed to the observed reduction in the drift. These are the first observations which indicate the effects of the dusk-to-dawn penetration electric fields on the east-west drifts during northward IMF.Citation: Sreeja, V., T. K. Pant, L. Jose, and S. Ravindran (2011), Westward electric field penetration to the dayside equatorial ionosphere during the main phase of the geomagnetic storm on 22

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