Long term variability in solar wind velocity and IMF intensity and the relationship between solar wind parameters & geomagnetic activity

Abstract

A study is carried out on the mean monthly values of in situ observations of solar wind velocity (V ) and the intensity of interplanetary magnetic field, B to elucidate their long term variations using the technique of singular spectrum analysis. It is shown that B exhibits a clear solar cycle signal with progressively deepening minimum and a well-defined longer period variation but V is marked by a ∼9-yr cycle. Time variations in the amplitude of 16-month periodicity, observed sporadically in the velocity earlier by others are clearly brought out, as also the characteristic amplitude changes in a 42-month signal in velocity. It appears that time intervals which show certain significant fluctuations in B are marked by the absence of similar signal in V .aa index is next used as a proxy for solar wind velocity, after establishing a good correlation between Ap and observed V so that we could examine the evolution of different periodicities over 14 solar cycles. A significant trend with least value in 1900 and a near-linear rise up to 1960 is shown to be the main feature of the velocity change. The solar cycle component in V lags the solar activity peak by ∼22 months. Streams emanating from coronal holes in the declining phase seem to be the most dominant contributor to the 11-year variation in velocity. The anomalous pattern of changes in V observed in cycle 20 is not present in any of the other 13 cycles.Statistical relationships between V , B and plasma density (N ) with Ap are studied and it is shown that over three solar cycles (20, 21 and 22) the patterns are almost the same with a slight change observed in cycle 21. IMF B and Ap are linearly related over a wide range of Ap values from close to 0 up to about 60, whereas density/ Ap relation appears insignificant. In case of V , an initial rapid rise in V causes moderate changes in Ap but for velocity in excess of 700 km/sec, the enhancement in geomagnetic activity is more rapid. From the statistical relation of several other solar wind/IMF parameters, their variability and combinations with Ap, one sees linear relation for solar wind electric field, n/s component of IMF and variability in the components of B. An estimate is made of the base level of the magnetosphere, corresponding to quiet levels of geomagnetic activity.

On the relationship of cosmic ray intensity with solar, interplanetary, and geophysical parameters

“…It is also expected that the correlation between IMF-B tot (nT) and V sw (km/s) will be much stronger during the LCRI than during the HCRI (see Table 3). The reason for the observed variation is probably that the IMF (nT) is controlled by the V sw (km/s), while the CRI is controlled by the IMF (nT), as suggested by a few researchers (Rangarajan and Barreto 2000;Mishra and Mishra 2008;Singh et al 2008).…”

Pickup ion measurements by MAVEN: A diagnostic of photochemical oxygen escape from Mars

“…Therefore, the necessary observations by SEP are possible given the presence of appropriate solar wind conditions and the absence of solar particle events. For an O + pickup ion to have a maximum energy of E max > 60 keV to be detected by SEP, solar wind speeds of 500 km/s or higher, with θ UB exceeding~50°, are needed, and statistically, such conditions occur~20% of the time [Rangarajan and Barreto, 2000;Jarvinen and Kallio, 2014]. During intense solar particle events, the flux of solar energetic particles associated with solar flares and coronal mass ejections will likely exceed the predicted pickup ion fluxes.…”

The Stratospheric and Mesospheric NOy in the 2002–2004 Polar Winters as measured by MIPAS/ENVISAT

“…In particular, in 1991, when the mean seasonal A p was largely increased, the profiles agree rather well. The electron precipitation activity is expected to have a solar cycle variability with larger values in the declining phase (Rangarajan and Barreto, 2000), e.g., in 1991 and 2003. Thus, the NO x values measured by MIPAS in the 2003 Antarctic winter were rather high within a decade time frame, but seem typical in the context of the solar cycle progression.…”