scholarly journals Large-scale velocity fluctuations in polar solar wind

2005 ◽  
Vol 23 (3) ◽  
pp. 1025-1031 ◽  
Author(s):  
B. Bavassano ◽  
R. Bruno ◽  
R. D'Amicis
Keyword(s):  
Solar Wind ◽  
Solar Activity ◽  
High Latitude ◽  
Large Scale ◽  
Activity Cycle ◽  
High Solar Activity ◽  
Time Lags ◽  
Polar Wind ◽  
Frequency Distributions ◽  
Long Range Correlations

Abstract. The 3-D structure of the solar wind varies dramatically along the Sun's activity cycle. In the present paper we focus on some properties of the polar solar wind. This is a fast, teneous, and steady flow (as compared to low-latitude conditions) that fills the high-latitude heliosphere at low solar activity. The polar wind has been extensively investigated by Ulysses, the first spacecraft to perform in-situ measurements in the high-latitude heliosphere. Though the polar wind is quite a uniform flow, fluctuations in its velocity do not appear negligible. A simple way to characterize the solar wind structure is that of performing a multi-scale statistical analysis of the wind velocity differences. The occurrence frequency distributions of velocity differences at time lags from 1 to 1024h and the corresponding values of mean, standard deviation, skewness, and kurtosis have been obtained. A comparison with previous results in ecliptic wind at both low and high solar activity has been performed. It comes out that the kind of trend observed in the distributions for changing scale is the same for the different solar wind regimes. Differences between different flows just have an effect on the values of the distribution moments and the scales at which the transition from non-Gaussian to Gaussian-like behaviours occurs. This is typical of systems in which random fluctuations are mixed to coherent structures of some characteristic size, in other words, systems where long-range correlations cannot be neglected.

scholarly journals Alfvénic fluctuations in "newborn"' polar solar wind

2005 ◽  
Vol 23 (4) ◽  
pp. 1513-1520 ◽  
Author(s):  
B. Bavassano ◽  
E. Pietropaolo ◽  
R. Bruno
Keyword(s):  
Solar Wind ◽  
Solar Activity ◽  
Solar Maximum ◽  
Activity Cycle ◽  
Residual Energy ◽  
Mhd Waves ◽  
Polar Wind ◽  
Interplanetary Physics ◽  
Low Latitudes ◽  
Comparative Statistical Analysis

Abstract. The 3-D structure of the solar wind is strongly dependent upon the Sun's activity cycle. At low solar activity a bimodal structure is dominant, with a fast and uniform flow at the high latitudes, and slow and variable flows at low latitudes. Around solar maximum, in sharp contrast, variable flows are observed at all latitudes. This last kind of pattern, however, is a relatively short-lived feature, and quite soon after solar maximum the polar wind tends to regain its role. The plasma parameter distributions for these newborn polar flows appear very similar to those typically observed in polar wind at low solar activity. The point addressed here is about polar wind fluctuations. As is well known, the low-solar-activity polar wind is characterized by a strong flow of Alfvénic fluctuations. Does this hold for the new polar flows too? An answer to this question is given here through a comparative statistical analysis on parameters such as total energy, cross helicity, and residual energy, that are of general use to describe the Alfvénic character of fluctuations. Our results indicate that the main features of the Alfvénic fluctuations observed in low-solar-activity polar wind have been quickly recovered in the new polar flows developed shortly after solar maximum. Keywords. Interplanetary physics (MHD waves and turbulence; Sources of the solar wind) – Space plasma physics (Turbulence)

scholarly journals Velocity fluctuations in polar solar wind: a comparison between different solar cycles

2009 ◽  
Vol 27 (2) ◽  
pp. 877-883 ◽  
Author(s):  
B. Bavassano ◽  
R. Bruno ◽  
R. D'Amicis
Keyword(s):  
Solar Wind ◽  
Wind Velocity ◽  
High Latitude ◽  
Coronal Holes ◽  
Dimensional Structure ◽  
Time Lags ◽  
Solar Cycles ◽  
Polar Wind ◽  
Activity Maximum ◽  
Velocity Fluctuations

Abstract. The polar solar wind is a fast, tenuous and steady flow that, with the exception of a relatively short phase around the Sun's activity maximum, fills the high-latitude heliosphere. The polar wind properties have been extensively investigated by Ulysses, the first spacecraft able to perform in-situ measurements in the high-latitude heliosphere. The out-of-ecliptic phases of Ulysses cover about seventeen years. This makes possible to study heliospheric properties at high latitudes in different solar cycles. In the present investigation we focus on hourly- to daily-scale fluctuations of the polar wind velocity. Though the polar wind is a quite uniform flow, fluctuations in its velocity do not appear negligible. A simple way to characterize wind velocity variations is that of performing a multi-scale statistical analysis of the wind velocity differences. Our analysis is based on the computation of velocity differences at different time lags and the evaluation of statistical quantities (mean, standard deviation, skewness, and kurtosis) for the different ensembles. The results clearly show that, though differences exist in the three-dimensional structure of the heliosphere between the investigated solar cycles, the velocity fluctuations in the core of polar coronal holes exhibit essentially unchanged statistical properties.

MEDIUM-TERM OSCILLATIONS OF THE SOLAR ACTIVITY

2021 ◽  
Vol 44 ◽  
pp. 85-91
Author(s):  
V.N. Obridko ◽  
◽  
D.D. Sokoloff ◽  
V.V. Pipin ◽  
A.S. Shibalova ◽  
...  
Keyword(s):  
Solar Activity ◽  
Activity Cycle ◽  
Solar Interior ◽  
Local Fields ◽  
Lower Atmosphere ◽  
High Solar Activity ◽  
Dynamo Model ◽  
Sunspot Activity ◽  
Geomagnetic Variations ◽  
Near Surface

In addition to the well-known 11-year cycle, longer and shorter characteristic periods can be isolated in variations of the parameters of helio-geophysical activity. Periods of about 36 and 60 years were revealed in variations of the geomagnetic activity and an approximately 60-year periodicity, in the evolution of correlation between the pressure in the lower atmosphere and the solar activity. Similar periods are observed in the cyclonic activity. Such periods in the parameters of the solar activity are difficult to identify because of a limited database available; however, they are clearly visible in variations of the asymmetry of the sunspot activity in the northern and southern solar hemispheres. In geomagnetic variations, one can also isolate oscillations with the characteristic periods of 5-6 years (QSO) and 2-3 years (QBO). We have considered 5-6-year periodicities (about half the main cycle) observed in variations of the sunspot numbers and the intensity of the dipole component of the solar magnetic field. A comparison with different magnetic dynamo models allowed us to determine the possible origin of these oscillations. A similar result can be reproduced in a dynamo model with nonlinear parameter variations. In this case, the activity cycle turns out to be anharmonic and contains other periodicities in addition to the main one. As a result of the study, we conclude that the 5-6-year activity variations are related to the processes of nonlinear saturation of the dynamo in the solar interior. Quasi-biennial oscillations are actually separate pulses related little to each other. Therefore, the methods of the spectral analysis do not reveal them over large time intervals. They are a direct product of local fields, are generated in the near-surface layers, and are reliably recorded only in the epochs of high solar activity.

scholarly journals A reconstruction of radiocarbon production and total solar irradiance from the Holocene <sup>14</sup>C and CO<sub>2</sub> records: implications of data and model uncertainties

2013 ◽  
Vol 9 (4) ◽  
pp. 1879-1909 ◽  
Author(s):  
R. Roth ◽  
F. Joos
Keyword(s):  
Solar Activity ◽  
Solar Irradiance ◽  
Surface Air Temperature ◽  
Total Solar Irradiance ◽  
Production Model ◽  
High Solar Activity ◽  
Solar Modulation ◽  
Time Lags ◽  
Instrumental Data ◽  
The Holocene

Abstract. Radiocarbon production, solar activity, total solar irradiance (TSI) and solar-induced climate change are reconstructed for the Holocene (10 to 0 kyr BP), and TSI is predicted for the next centuries. The IntCal09/SHCal04 radiocarbon and ice core CO2 records, reconstructions of the geomagnetic dipole, and instrumental data of solar activity are applied in the Bern3D-LPJ, a fully featured Earth system model of intermediate complexity including a 3-D dynamic ocean, ocean sediments, and a dynamic vegetation model, and in formulations linking radiocarbon production, the solar modulation potential, and TSI. Uncertainties are assessed using Monte Carlo simulations and bounding scenarios. Transient climate simulations span the past 21 thousand years, thereby considering the time lags and uncertainties associated with the last glacial termination. Our carbon-cycle-based modern estimate of radiocarbon production of 1.7 atoms cm−2 s−1 is lower than previously reported for the cosmogenic nuclide production model by Masarik and Beer (2009) and is more in-line with Kovaltsov et al. (2012). In contrast to earlier studies, periods of high solar activity were quite common not only in recent millennia, but throughout the Holocene. Notable deviations compared to earlier reconstructions are also found on decadal to centennial timescales. We show that earlier Holocene reconstructions, not accounting for the interhemispheric gradients in radiocarbon, are biased low. Solar activity is during 28% of the time higher than the modern average (650 MeV), but the absolute values remain weakly constrained due to uncertainties in the normalisation of the solar modulation to instrumental data. A recently published solar activity–TSI relationship yields small changes in Holocene TSI of the order of 1 W m−2 with a Maunder Minimum irradiance reduction of 0.85 ± 0.16 W m−2. Related solar-induced variations in global mean surface air temperature are simulated to be within 0.1 K. Autoregressive modelling suggests a declining trend of solar activity in the 21st century towards average Holocene conditions.

scholarly journals Breathing of heliospheric structures triggered by the solar-cycle activity

2003 ◽  
Vol 21 (6) ◽  
pp. 1303-1313 ◽  
Author(s):  
K. Scherer ◽  
H. J. Fahr
Keyword(s):  
Solar Wind ◽  
Solar Activity ◽  
Solar Cycle ◽  
Activity Cycle ◽  
Periodic Variation ◽  
Galactic Cosmic Rays ◽  
Activity Period ◽  
Solar Cycles ◽  
Interplanetary Physics ◽  
Ram Pressure

Abstract. Solar wind ram pressure variations occuring within the solar activity cycle are communicated to the outer heliosphere as complicated time-variabilities, but repeating its typical form with the activity period of about 11 years. At outer heliospheric regions, the main surviving solar cycle feature is a periodic variation of the solar wind dynamical pressure or momentum flow, as clearly recognized by observations of the VOYAGER-1/2 space probes. This long-periodic variation of the solar wind dynamical pressure is modeled here through application of appropriately time-dependent inner boundary conditions within our multifluid code to describe the solar wind – interstellar medium interaction. As we can show, it takes several solar cycles until the heliospheric structures adapt to an average location about which they carry out a periodic breathing, however, lagged in phase with respect to the solar cycle. The dynamically active heliosphere behaves differently from a static heliosphere and especially shows a historic hysteresis in the sense that the shock structures move out to larger distances than explained by the average ram pressure. Obviously, additional energies are pumped into the heliosheath by means of density and pressure waves which are excited. These waves travel outwards through the interface from the termination shock towards the bow shock. Depending on longitude, the heliospheric sheath region memorizes 2–3 (upwind) and up to 6–7 (downwind) preceding solar activity cycles, i.e. the cycle-induced waves need corresponding travel times for the passage over the heliosheath. Within our multifluid code we also adequately describe the solar cycle variations in the energy distributions of anomalous and galactic cosmic rays, respectively. According to these results the distribution of these high energetic species cannot be correctly described on the basis of the actually prevailing solar wind conditions.Key words. Interplanetary physics (heliopause and solar wind termination; general or miscellaneous) – Space plasma physics (experimental and mathematical techniques)

scholarly journals Implementing the MULTI-VP coronal model in EUHFORIA: Test case results and comparisons with the WSA coronal model

2021 ◽  
Vol 648 ◽  
pp. A35
Author(s):  
E. Samara ◽  
R. F. Pinto ◽  
J. Magdalenić ◽  
N. Wijsen ◽  
V. Jerčić ◽  
...  
Keyword(s):  
Solar Wind ◽  
Solar Activity ◽  
High Speed ◽  
Weather Prediction ◽  
Solar Wind Plasma ◽  
High Solar Activity ◽  
Source Surface ◽  
Field Source ◽  
Magnetic Signatures

Context. In this study, we focus on improving EUHFORIA (European Heliospheric Forecasting Information Asset), a recently developed 3D magnetohydrodynamics space weather prediction tool. The EUHFORIA model consists of two parts covering two spatial domains: the solar corona and the inner heliosphere. For the first part, the semiempirical Wang-Sheeley-Arge (WSA) model is used by default; this model employs the potential field source surface and Schatten current sheet models to provide the necessary solar wind plasma and magnetic conditions above the solar surface, at 0.1 AU, which serve as boundary conditions for the inner heliospheric part. Herein, we present the first results of the implementation of an alternative coronal model in EUHFORIA, the so-called MULTI-VP model. Aims. After we replace the default EUHFORIA coronal setup with the MULTI-VP model, we compare their outputs both at 0.1 AU and 1 AU, for test cases involving high speed wind streams (HSSs). We select two distinct cases in which the standard EUHFORIA setup failed to reproduce the HSS plasma and magnetic signatures at Earth to test the performance of MULTI-VP coupled with EUHFORIA-heliosphere. Methods. To understand the quality of modeling with MULTI-VP in comparison with the default coronal model in EUHFORIA, we considered one HSS case during a period of low solar activity and another one during a period of high solar activity. Moreover, the modeling of the two HSSs was performed by employing magnetograms from different providers: one from the Global Oscillation Network Group (GONG) and the second from the Wilcox Space Observatory (WSO). This way, we were able to distinguish differences arising not only because of the different models but also because of different magnetograms. Results. The results indicate that when employing a GONG magnetogram, the combination MULTI-VP+EUHFORIA-heliosphere reproduces the majority of HSS plasma and magnetic signatures measured at L1. On the contrary, the standard WSA+EUHFORIA-heliosphere combination does not capture the arrival of the HSS cases at L1. When employing WSO magnetograms, MULTI-VP+EUHFORIA-heliosphere reproduces the HSS that occurred during the period of high solar activity. However, it is unclear if it models the HSS during the period of low solar activity. For the same magnetogram and periods of time, WSA+EUHFORIA-heliosphere is not able to capture the HSSs of interest. Conclusions. The results show that the accuracy of the simulation output at Earth depends on the choice of both the coronal model and input magnetogram. Nevertheless, a more extensive statistical analysis is necessary to determine how precisely these choices affect the quality of the solar wind predictions.

scholarly journals THE STRUCTURE OF THE SOLAR WIND IN THE HELIOSPHERE DEPENDING ON THE PHASE OF THE SOLAR CYCLE: LARGE-SCALE DYNAMICS OF THE HELIOSPHERIC CURRENT SHEET

2019 ◽  
Vol 47 (1) ◽  
pp. 85-87
Author(s):  
E.V. Maiewski ◽  
R.A. Kislov ◽  
H.V. Malova ◽  
O.V. Khabarova ◽  
V.Yu. Popov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Solar Activity ◽  
Solar Cycle ◽  
Current Sheet ◽  
Heliospheric Current Sheet ◽  
High Solar Activity ◽  
The Sun ◽  
High Latitudes ◽  
The Magnetic Field

A stationary axisymmetric MHD model of the solar wind has been constructed, which allows us to study the spatial distribution of the magnetic field and plasma characteristics at radial distances from 20 to 400 radii of the Sun at almost all heliolatitudes. The model takes into account the changes in the magnetic field of the Sun during a quarter of the solar cycle, when the dominant dipole magnetic field is replaced by a quadrupole. Selfconsistent solutions for the magnetic and velocity fields, plasma concentration and current density of the solar wind depending on the phase of the solar cycle are obtained. It is shown that during the domination of the dipole magnetic component in the solar wind heliospheric current sheet (HCS) is located in the equatorial plane, which is a part of the system of radial and transverse currents, symmetrical in the northern and southern hemispheres. As the relative contribution of the quadrupole component to the total magnetic field increases, the shape of the HCS becomes conical; the angle of the cone gradually decreases, so that the current sheet moves entirely to one of the hemispheres. At the same time, at high latitudes of the opposite hemisphere, a second conical HCS arises, the angle of which increases. When the quadrupole field becomes dominant (at maximum solar activity), both HCS lie on conical surfaces inclined at an angle of 35 degrees to the equator. The model describes the transition from the fast solar wind at high latitudes to the slow solar wind at low latitudes: a relatively gentle transition in the period of low solar activity gives way to more drastic when high solar activity. The model also predicts an increase in the steepness of the profiles of the main characteristics of the solar wind with an increase in the radial distance from the Sun. Comparison of the obtained dependences with the available observational data is discussed.

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