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Dive into the research topics where T. V. Laitinen is active.

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Featured researches published by T. V. Laitinen.


Geophysical Research Letters | 2006

Compression of the Earth's magnetotail by interplanetary shocks directly drives transient magnetic flux closure

Benoît Hubert; M. Palmroth; T. V. Laitinen; Pekka Janhunen; S. E. Milan; Adrian Grocott; S. W. H. Cowley; Tuija I. Pulkkinen; Jean-Claude Gérard

We use a novel method to evaluate the global opening and closure of magnetic flux in the terrestrial system, and to analyse two interplanetary shock passages that occurred during magnetically quiet periods. We find that, even under these quiet conditions, where the amount of open flux was already low, the compression of the magnetotail by the shocks still created intense but short-lived bursts of flux closure reaching ∼130 kV, comparable to values obtained shortly after a substorm onset, although no expansion phase developed. The results, supported by a global MHD simulation of the space environment, point to a trigger mechanism of flux closure directly driven by the solar wind compression, independent of the usual substorm expansion phase process.


In: Liu, W and Fujimoto, M, (eds.) The Dynamic Magnetosphere. (pp. 29-37). Springer Netherlands (2011) | 2011

Quantifying Energy Transfer at the Magnetopause

M. Palmroth; H. Koskinen; Tuija I. Pulkkinen; C.R. Anekallu; T. V. Laitinen; Elizabeth A. Lucek; Iannis Dandouras

We review recently developed methods to investigate energy circulation in the near-Earth space using a global magnetohydrodynamic (MHD) simulation GUMICS-4. We describe methods to evaluate the magnetopause energy transfer and ways to quantify effects of the reconnection dynamics. We also present evidence, supported by Cluster spacecraft observations, showing that the interplanetary magnetic field (IMF) y component controls the spatial variation of the magnetopause energy transfer. The simulation results also suggests that the energy transfer exhibits a “hysteresis” effect where the energy transfer does not decrease immediately after the driving conditions start to become weaker. We investigate the hysteresis effect in the simulation and conclude that the previous driving conditions as well as the present state of the global magnetosphere may influence the processes at the magnetopause, and thus regulate the energy input to the system.


Journal of Geophysical Research | 2015

A method to predict thermospheric mass density response to geomagnetic disturbances using time‐integrated auroral electrojet index

Juho Iipponen; T. V. Laitinen

Using the thermospheric mass density measurements from the European Space Agencys Gravity field and steady state Ocean Circulation Explorer (GOCE) satellite, we develop a new empirical geomagnetic disturbance time correction based on integrating the auroral electrojet (AE) index. For this, a US Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar (NRLMSISE-00) model with no geomagnetic parametrization is subtracted from the GOCE densities, and the regressions between the time-integrated AE index and density residuals are computed as a function of latitude, solar time, and day of year. When we add this correction to the quiet time reference NRLMSISE-00 model, it increases the models disturbance time correlation with the 270 km normalized GOCE densities from 0.71 to 0.86. We assess the effect of integrating thermospheric density proxies with respect to time using both geomagnetic and solar indices and discover that the integration of AE, ap, and the epsilon parameter significantly increase their correlation with the orbit-averaged GOCE densities. We compare the predictions of our empirical correction with the NRLMSISE-00 and Jacchia-Bowman (JB2008) models, and significant deviations from the measurements are discovered. The NRLMSISE-00 is confirmed to generally underestimate the density enhancement, and the latitudinal shape of the predicted response shows too low enhancements at middle latitudes. Even though these are not issues for the JB2008 model, it performs weaker than the NRLMSISE-00 at reproducing the orbit-averaged densities. This unexpected result is attributed to the weakness of the ap parametrization, which is used in the model during smaller disturbances.


Physics of Plasmas | 2014

Forcing continuous reconnection in hybrid simulations

T. V. Laitinen; Riku Jarvinen; E. Kallio; Pekka Janhunen

We have performed hybrid simulations of driven continuous reconnection with open boundary conditions. Reconnection is started by a collision of two subsonic plasma fronts with opposite magnetic fields, without any specified magnetic field configuration as initial condition. Due to continued forced plasma inflow, a current sheet co-located with a dense and hot plasma sheet develops. The translational symmetry of the current sheet is broken by applying a spatial gradient in the inflow speed. We compare runs with and without localized resistivity: reconnection is initiated in both cases, but localized resistivity stabilizes it and enhances its efficiency. The outflow speed reaches about half of Alfven speed. We quantify the conversion of magnetic energy to kinetic energy of protons and to Joule heating and show that with localized resistivity, kinetic energy of protons is increased on average five-fold in the reconnection in our simulation case.


Journal of Atmospheric and Solar-Terrestrial Physics | 2012

The GUMICS-4 global MHD magnetosphere-ionosphere coupling simulation

Pekka Janhunen; M. Palmroth; T. V. Laitinen; I. Honkonen; L. Juusola; G. Facskó; Tuija I. Pulkkinen


Annales Geophysicae | 2012

Supermagnetosonic subsolar magnetosheath jets and their effects: from the solar wind to the ionospheric convection

H. Hietala; N. Partamies; T. V. Laitinen; L. B. N. Clausen; Gabor Facsko; Andris Vaivads; H. E. J. Koskinen; Iannis Dandouras; H. Rème; E. Lucek


Journal of Geophysical Research | 2007

Continuous reconnection line and pressure‐dependent energy conversion on the magnetopause in a global MHD model

T. V. Laitinen; M. Palmroth; Tuija I. Pulkkinen; P. Janhunen; H. E. J. Koskinen


Annales Geophysicae | 2006

On the characterization of magnetic reconnection in global MHD simulations

T. V. Laitinen; Pekka Janhunen; Tuija I. Pulkkinen; M. Palmroth; H. E. J. Koskinen


Journal of Geophysical Research | 2010

Magnetospheric modes and solar wind energy coupling efficiency

Tuija I. Pulkkinen; M. Palmroth; H. E. J. Koskinen; T. V. Laitinen; Charles C. Goodrich; V. G. Merkin; J. G. Lyon


Annales Geophysicae | 2006

Magnetopause energy and mass transfer: results from a global MHD simulation

M. Palmroth; T. V. Laitinen; Tuija I. Pulkkinen

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M. Palmroth

University of Helsinki

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Hannu E. J. Koskinen

Swedish Institute of Space Physics

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H. E. J. Koskinen

Finnish Meteorological Institute

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C.R. Anekallu

Finnish Meteorological Institute

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H. Rème

University of Toulouse

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