Timo Asikainen

University of Oulu · Space Climate Research Unit

The Earth’s atmosphere is influenced by energetic electrons coming from the magnetosphere. This energetic electron precipitation (EEP) is energized by the solar wind and directly affects in the high‐latitude mesosphere and lower thermosphere (MLT). EEP forms odd nitrogen (NOx) and hydrogen oxides (HOx) which destroy ozone. During winter EEP‐NOx des...

Context. The Sun experienced a period of unprecedented activity during the 20th century, now called the Modern Maximum (MM). The decay of the MM after its maximum in cycle 19 has changed the Sun, the heliosphere, and the planetary environments in many ways. However, studies disagree on whether this decay has proceeded synchronously in different sol...

It is known that electricity consumption in many cold Northern countries depends greatly on prevailing outdoor temperatures especially during the winter season. On the other hand, recent research has demonstrated that solar wind driven energetic particle precipitation from space into the polar atmosphere can influence the stratospheric polar vortex...

Here we study the prediction of even and odd numbered sunspot cycles separately, thereby taking into account the Hale cyclicity of solar magnetism. We first show that the temporal evolution and shape of all sunspot cycles are extremely well described by a simple parameterized mathematical expression. We find that the parameters describing even suns...

Here we study the prediction of even and odd numbered sunspot cycles separately, thereby taking into account the Hale cyclicity of solar magnetism. We first show that the temporal evolution and shape of all sunspot cycles are extremely well described by a simple parameterized mathematical expression. We find that the parameters describing even suns...

The polar vortex is a strong jet of westerly wind which forms each winter around the polar stratosphere. Sometimes, roughly every other winter, the polar vortex in the Northern Hemisphere experiences a dramatic breakdown and associated warming of the polar stratosphere. Such events are called sudden stratospheric warmings (SSWs) and they are known...

Here we study the prediction of even and odd numbered sunspot cycles separately, thereby taking into account the Hale cyclicity of solar magnetism. We first show that the temporal evolution and shape of all sunspot cycles are extremely well described by a simple parameterized mathematical expression. We find that the parameters describing even suns...

We study the occurrence of magnetic storms in space age (1957–2021) using Dst and Dxt indices. We find 2,526/2,743 magnetic storms in the Dxt/Dst index, out of which 45% are weak, 40% moderate, 12% intense and 3% major storms. Occurrence of storms in space age follows the slow decrease of sunspot activity and the related change in solar magnetic st...

We study the occurrence of magnetic storms in space age (1957-2021) using Dst and Dxt indices. We find 2526/2743 magnetic storms in the Dxt/Dst index, out of which 45% are weak, 40% moderate, 12% intense and 3% major storms. Occurrence of storms in space age follows the slow decrease of sunspot activity and the related change in solar magnetic stru...

In this study, we use mutual information from information theory to investigate non-linear correlation between geomagnetic activity indicated by auroral electrojet (AE) index with both the global ultra low frequency (ULF) Pc5 wave power and medium energy (≥30 keV) electron precipitation at the central outer radiation belt. To investigate the energy...

In the recent years, significant attention has been given to the combined effect of Interplanetary Magnetic Field (IMF) duskward component (By) and dipole tilt on the global magnetosphere-ionosphere system response. Numerous studies have pointed out that when the Earth's magnetic dipole is tilted away from the Sun (negative dipole tilt during north...

The Mansurov effect is related to the interplanetary magnetic field (IMF) and its ability to modulate the global electric circuit, which is further hypothesized to impact the polar troposphere through cloud generation processes. We investigate the connection between IMF By-component and polar surface pressure by using daily ERA5 reanalysis for geop...

Plain Language Summary Electrons from the near‐Earth space constantly precipitate to the Earth's upper atmosphere. Intensity of this electron precipitation is controlled by solar wind, a plasma stream flowing from the Sun. Precipitating electrons form ozone‐depleting compounds which descend down to the stratosphere during the winter. Electron preci...

Precipitating auroral and radiation belt electrons are considered to play an important part in the natural forcing of the middle atmosphere with a possible impact on the climate system. Recent studies suggest that this forcing is underestimated in current chemistry‐climate models. The HEPPA III intercomparison experiment is a collective effort to a...

Precipitating auroral and radiation belt electrons are considered an important part of the natural forcing of the climate system. Recent studies suggest that this forcing is underestimated in current chemistry‐climate models. The High Energy Particle Precipitation in the Atmosphere III intercomparison experiment is a collective effort to address th...

Geomagnetic activity is mainly driven by the southward (Bz) component of the interplanetary magnetic field (IMF), which dominates all solar wind coupling functions. Coupling functions also depend on the absolute value of the dawn‐dusk (By) component of the IMF, but not on its sign. However, recent studies have shown that for a fixed level of solar...

Coronal holes (CHs) are regions in the solar corona characterized by plasma density lower than in the surrounding quiet Sun. Therefore they appear dark in images of the solar atmosphere made, e.g., in extreme ultraviolet (EUV). Identifying CHs on solar images is difficult since CH boundaries are not sharp, but typically obscured by magnetic structu...

Northern polar vortex experiences significant variability during Arctic winter. Solar activity contributes to this variability via solar irradiance and energetic particle precipitation. Recent studies have found that energetic electron precipitation (EEP) affects the polar vortex by forming ozone depleting NOx compounds. However, it is still unknow...

Recently, it has been established that interplanetary coronal mass ejections (ICMEs) can dramatically affect both trapped electron fluxes in the outer radiation belt and precipitating electron fluxes lost from the belt into the atmosphere. Precipitating electron fluxes and energies can vary over a range of timescales during these events. These vari...

The Northern polar vortex experiences considerable interannual variability, which is also reflected to tropospheric weather. Recent research has established a link between polar vortex variations and energetic electron precipitation (EEP) from the near‐Earth space into the polar atmosphere, which is mediated by EEP‐induced chemical changes causing...

We study here energetic-electron (E>30 keV) precipitation using cosmic noise absorption (CNA) during the sheath and ejecta structures of 61 interplanetary coronal mass ejections (ICMEs) observed in the near-Earth solar wind between 1997 and 2012. The data come from the Finnish riometer (relative ionospheric opacity meter) chain from stations extend...

Recently, it has been established that interplanetary coronal mass ejections (ICMEs) can dramatically affect both trapped electron fluxes in the outer radiation belt and precipitating electron fluxes lost from the belt into the atmosphere. Precipitating electron flux and energy can vary over a range of timescales during these events. These variatio...

Plain Language Summary During some winters the cold polar stratosphere experiences a strong and sudden warming. These sudden stratospheric warmings (SSW) can affect greatly the surface weather in northern Europe and in North America. However, the factors that contribute to the formation of sudden warmings are not entirely known. We study how the tw...

The most important driver of geomagnetic activity is the north–south ( Bz) component of the interplanetary magnetic field (IMF), which dominates the solar wind‐magnetosphere coupling and all solar wind coupling functions. While the east–west ( By) IMF component is also included in most coupling functions, its effect is always assumed to be symmetri...

Synoptic maps of solar EUV intensities have been constructed for many decades in order to display the distribution of the different EUV emissions across the solar surface, with each map representing one Carrington rotation (i.e. one rotation of the Sun). This article presents a new solar EUV synoptic map dataset based on full-disk images from the S...

Abstract. We study here energetic ( E > 30 keV) electron precipitation using cosmic noise absorption (CNA) during the sheath and ejecta structures of 61 interplanetary coronal mass ejections (ICMEs) observed in the near-Earth solar wind between 1997 and 2012. The data comes from the Finnish riometer chain from stations extending from auroral (IVA,...

Synoptic maps of solar EUV intensities have been constructed for many decades in order to display the distribution of the different EUV emissions across the solar surface, with each map representing one Carrington rotation (i.e., one rotation of the Sun). This paper presents a new solar EUV synoptic map dataset based on full-disk images from Solar...

Recent studies suggest a response in the North Atlantic winter circulation which lags by a couple of years with respect to sunspot maximum. This has been explained by two different top‐down mechanisms: a solar wind driven particle effect in the polar atmosphere during the declining phase of the solar cycle, and the re‐emergence and amplification of...

Today, the near‐Earth space is facing a paradigm change as the number of new spacecraft is literally skyrocketing. Increasing numbers of small satellites threaten the sustainable use of space, as without removal, space debris will eventually make certain critical orbits unusable. A central factor affecting small spacecraft health and leading to deb...

One of the most popular long‐term data sets of energetic particles used in, for example, long‐term radiation belt studies and in atmospheric/climate studies is perhaps the NOAA/POES (Polar Orbiting Environmental Satellites) data set, which extends nearly continuously from 1979 to present. The present study aims to construct a new homogeneous long‐t...

Energetic electron precipitation (EEP) affects the high‐latitude middle atmosphere by producing NOX compounds that destroy ozone. Earlier studies have shown that in the wintertime polar stratosphere, increased EEP enhances the westerly wind surrounding the pole, the polar vortex. This EEP effect has been found to depend on the quasi‐biennial oscill...

Today, the near-Earth space is facing a paradigm change as the number of new spacecraft is literally sky-rocketing. Increasing numbers of small satellites threaten the sustainable use of space, as without removal, space debris will eventually make certain critical orbits unusable. A central factor affecting small spacecraft health and leading to de...

One of the most popular long‐term data sets of energetic particles used in, for example, long‐term radiation belt studies and in atmospheric/climate studies is perhaps the National Oceanic and Atmospheric Administration/Polar Orbiting Environmental Satellites (POES) data set, which extends nearly continuously from 1979 to present. The energetic par...

Northern Hemisphere winter circulation is affected by both solar and terrestrial forcings. El-Niño events and volcanic eruptions have been shown to produce a negative and a positive North Atlantic Oscillation (NAO) signature, respectively. Recent studies show a positive NAO signature related to both geomagnetic activity (proxy for solar wind driven...

Coronal holes (CH) are regions of open magnetic field lines in the solar corona and the source of fast solar wind. Understanding the evolution of coronal holes is critical for solar magnetism as well as for accurate space weather forecasts. We study here the extreme ultraviolet (EUV) synoptic maps at three wavelengths (195A/193A, 171A and 304A) mea...

Certain limitations that have been identified in existing ionospheric prediction capabilities indicate that the deeper understanding and the accurate formulation of the ionospheric response to external forcing remain always high priority tasks for the research community. In this respect, this paper attempts an investigation of the long-term behavio...

Mutually conflicting results have been presented in earlier studies on the long-term relation of geomagnetic activity (GA) and the winter northern annular mode (NAM) and its modulation by quasi-biennial oscillation (QBO). Some studies have found a stronger positive relation in the easterly phase of the QBO, while in other studies a stronger positiv...

Disturbances of near-Earth space are predominantly driven by coronal mass ejections (CMEs) mostly originating from sunspots and high-speed solar wind streams (HSSs) emanating from coronal holes. Here we study the relative importance of CMEs and HSSs as well as slow solar wind in producing energetic electron precipitation. We use the recently correc...

A solid understanding of the solar wind control of ground magnetic field disturbances is essential for utilizing the existing long time series of ground data to obtain information on solar wind-magnetosphere-ionosphere coupling. We have used 20 years of International Monitor for Auroral Geomagnetic Effects magnetometer data (54°–76° magnetic latitu...

In this paper, we study two sets of local geomagnetic indices from 26 stations using the principal component (PC) and the independent component (IC) analysis methods. We demonstrate that the annually averaged indices can be accurately represented as linear combinations of two first components with weights systematically depending on latitude. We sh...

Several recent studies have found variability in the Northern Hemisphere winter climate related to different parameters of solar activity. While these results consistently indicate some kind of solar modulation of tropospheric and stratospheric circulation and surface temperature, opinions on the exact mechanism and the solar driver differ. Propose...

We study the latitudinal distribution of geomagnetic activity in 1966–2009 with local geomagnetic activity indices at 26 magnetic observatories. Using the principal component analysis method we find that more than 97% of the variance in annually averaged geomagnetic activity can be described by the two first principal components. The first componen...

We study the relationship between energetic 120–250 keV proton fluxes and geomagnetic Ap, AE, Dxt indices using the recently corrected measurements of the MEPED instrument onboard the low-altitude NOAA/POES satellites. Corrected database spans from 1979 to present, and allows us to reliably study the long-term variation of energetic proton fluxes o...

In this paper, we have improved the capabilities of a low dimensional nonlinear dynamical model called WINDMI to determine the state of the global magnetosphere by employing the magnetotail (MT) index as a measurement constraint during large geomagnetic storms. The MT index is derived from particle precipitation measurements made by the NOAA/POES s...

The Medium Energy Proton and Electron Detector (MEPED) instruments onboard the NOAA/POES satellites have provided a valuable long-term database of low-altitude energetic particle observations spanning from 1978 to present. Here we study the instrumental problems of the NOAA/MEPED electron detectors and present methods to correct them. It is well kn...

Recent research has shown that energetic particle precipitation into the upper atmosphere can change ion and neutral chemistry, e.g., by enhancing NO(x)concentration in the mesosphere, which, in turn, can affect stratospheric ozone balance under appropriate conditions. It has been suggested that this may affect the surface temperatures at high lati...

We report here on new problems in the NOAA/MEPED instruments and the related energetic proton dataset. These problems are solved, and the implied modifications to the earlier recalibration of the dataset are evaluated and adopted. We show that, besides degrading due to radiation damage, the NOAA-12 and NOAA-08 satellites suffer from increased elect...

When studying the effects of geomagnetic variability on the Earth's atmosphere reliable sources of quality long term data are essential. Most past studies concerning the effects of energetic particles precipitating from the magnetosphere into the atmosphere have been forced to use geomagnetic activity indices such as Kp (and Ap) as proxies for the...

It is well known that, in addition to the ring current, also other current systems like the magnetopause currents and the tail current have a significant contribution to the Dcx index. While the effect of the magnetopause currents are typically removed by correcting for the solar wind pressure, the effects of the tail current are less well understo...

Several studies suggest that energetic particle precipitation into the upper atmosphere can cause notable changes in ion and neutral chemistry in the upper and middle atmosphere. During polar winter these changes can last long enough to descend down to the stratospheric levels. Some recent studies also suggest a link between global geomagnetic acti...

The MEPED instruments onboard the low-altitude polar orbiting NOAA/POES satellites have measured energetic particles since 1978, offering a nearly continuous series of energetic particle fluxes in the magnetosphere during three solar cycles. However, there are several problems in using these data for long-term studies, the most significant one bein...

We present a new semiempirical model describing the contributions of the ring, tail, and magnetopause currents to the Dcx index. We use the isotropic boundary (IB) location of energetic particles measured by the NOAA/POES satellites, as a proxy for the tail current strength. Using local linear regression, we derive the model parameters and their fu...

Energetic particles have been persistently observed in the exterior cusp by different satellite missions such as POLAR, Cluster-II, Viking, ISEE etc. Yet the source and the acceleration mechanism of these particles have remained unclear. In this paper I review our studies of energetic particles in the cusp and the nearby high-latitude region of clo...

Here we study energetic electron fluxes in the inner radiation belt (L<2), especially within the South Atlantic Anomaly (SAA) region during a period of a few months using data from the low-altitude NOAA-15 and 16 satellites. Observations by these two spacecraft can yield long-term measurements of energetic electron fluxes at four different local ti...

The simple model of reconnected field line motion developed by Cooling et al. (2001) has been used in several recent case studies to explain the motion of flux transfer events across the magnetopause. We examine 213 FTEs observed by all four Cluster spacecraft under a variety of IMF conditions between November 2002 and June 2003, when the spacecraf...

In this paper we study flux transfer events (FTE) observed at the post-noon edge of the exterior cusp region by Cluster satellites. During the outbound dayside orbit on 2 February 2003, intense bursts of energetic particles were observed in close conjuction with magnetic field FTE signatures by the RAPID instrument onboard the Cluster 4. The pitch-...

A recent study by Asikainen and Mursula 2005 showed that at least during great magnetic storms the South Atlantic Anomaly SAA can reduce the eastward drift speed of energetic electrons at low invariant latitudes leading to their effective trapping within the SAA region Here we study energetic particle fluxes observed within the SAA region during a...

We study the energetic electrons by the Cluster-II Rapid instrument on a dayside high-latitude pass on the night between March 21/22, 2001. The Cluster satellites were flying outward in the pre-noon sector, passing a cusp/cleft type region roughly at midnight. Contrary to earlier observations of high fluxes of energetic particles in the high-latitu...

We study the global properties of energetic (>30 keV) particles during the main and early recovery phase of a major magnetic storm of March 31, 2001, using data of the NOAA 15 and 16 and the CLUSTER satellites. During the storm main phase the ring current energetic electron and ion fluxes were increased by nearly two orders of magnitude, and the fl...

In this paper we study the fluxes of energetic protons (30–4000 keV) and electrons (20–400 keV) in the exterior cusp and in the adjacent high-latitude dayside plasma sheet (HLPS) with the Cluster/RAPID instrument. Using two sample orbits we demonstrate that the Cluster observations at high latitudes can be dramatically different because the satelli...

We study energetic particles in the inner magnetosphere during the great storm of March 31, 2001, using low-altitude NOAA-15 and 16 satellites. The NOAA/SEM-2 instruments can monitor energetic particles above 30 keV from the equator to nearly polar latitudes. The South Atlantic anomaly (SAA) is seen by NOAA/SEM-2 as a region of an increased flux of...

We study the global properties of energetic particles during the main and early recovery phase of a major magnetic storm of March 31, 2001, using data of the NOAA-15 and 16 and the CLUSTER satellites. During the storm main phase the ring current energetic electron and ion fluxes were increased by nearly two orders of magnitude, and the flux maxima...

We study the global properties of energetic particles during the main and early recovery phase of a major magnetic storm of March 31, 2001, using data of the NOAA 15 and 16 and the four CLUSTER satellites. During the storm main phase the ring current energetic electron and ion fluxes are increased by nearly two orders of magnitude, and the flux max...

The CLUSTER-II EFW (Electric Fields and Waves) instrument measures the two spin-plane components of the electric field with a nominal sampling rate of 25 samples/second. This covers, e.g., the frequency range of equatorially generated electromagnetic ion cyclotron (EMIC) waves. Simultaneous observation of EMIC waves by several satellites has previo...

Around vernal equinoxes the Cluster-II satellites have their apogee in the noon sector, passing through the dayside high-latitude magnetosphere. In an earlier event study using the Cluster-II/Rapid instrument we have shown that there is a considerable flux of energetic particles in the closed field lines of the high-latitude magnetosphere. Instead,...

We study energetic particle observations during the main phase of the March 31, 2001, storm using the low-altitude NOAA satellites and the four Cluster satellites. The NOAA satellites are used to monitor the change of the global magnetospheric configuration. At the start of the main phase, the polar cap boundaries extend equatorwards and energetic...