L. Didkovsky - Academia.edu (original) (raw)

Papers by L. Didkovsky

The Extreme ultraviolet Variability Experiment (EVE) onboard Solar Dynamic Observatory (SDO), par... more The Extreme ultraviolet Variability Experiment (EVE) onboard Solar Dynamic Observatory (SDO), part of NASA's Living With the Star (LWS) program launched on 11 February 2010. Normal science operations began 1 May 2010 and have continued uninterrupted since then. The EVE instruments measure the solar extreme ultraviolet (EUV) irradiance from 0.1 to 105 nm with unprecedented spectral resolution (0.1 nm), temporal cadence (10 sec minimum), and accuracy (20% or better). Here, we present a review of the first year of EVE observations and initial science results presented at the LWS/SDO-1 Workshop held 1-5 May 2011 in Squaw Valley, CA. Much of the initial science from EVE has focused on the changes in the EUV irradiance due to solar flares. In the first eleven months of science operations, EVE observed over 350 C-class flares, 43 M-class flares, and 2 X-class flares. The location of a solar flare is important for understanding the EUV irradiance. ESP data is available in near-real time...

The Astrophysical Journal, 2011

ABSTRACT We report on the detection of oscillations in the corona in the frequency range correspo... more ABSTRACT We report on the detection of oscillations in the corona in the frequency range corresponding to five-minute acoustic modes of the Sun. The oscillations have been observed using soft X-ray measurements from the Extreme Ultraviolet Spectrophotometer (ESP) of the Extreme Ultraviolet Variability Experiment on board the Solar Dynamics Observatory. The ESP zeroth-order channel observes the Sun as a star without spatial resolution in the wavelength range of 0.1-7.0 nm (the energy range is 0.18-12.4 keV). The amplitude spectrum of the oscillations calculated from six-day time series shows a significant increase in the frequency range of 2-4 mHz. We interpret this increase as a response of the corona to solar acoustic (p) modes and attempt to identify p-mode frequencies among the strongest peaks. Due to strong variability of the amplitudes and frequencies of the five-minute oscillations in the corona, we study how the spectrum from two adjacent six-day time series combined together affects the number of peaks associated with the p-mode frequencies and their amplitudes. This study shows that five-minute oscillations of the Sun can be observed in the corona in variations of the soft X-ray emission. Further investigations of these oscillations may improve our understanding of the interaction of the oscillation modes with the solar atmosphere, and the interior-corona coupling, in general.

The Extreme ultraviolet Variability Experiment (EVE) aboard the NASA Solar Dynamics Observatory (... more The Extreme ultraviolet Variability Experiment (EVE) aboard the NASA Solar Dynamics Observatory (SDO) was launched on 11 February 2010. The EVE instruments measure the solar extreme ultraviolet (EUV) irradiance from 0.1 to 105 nm with unprecedented spectral resolution (0.1 nm), temporal cadence (10 sec minimum), and accuracy (20% or better). The highly variable solar EUV irradiance is a key measurement for the NASA Living With the Star (LWS) program as it is the major energy input into the Earth's upper atmosphere and thus impacts the geospace environment that affects satellite operations and communication and navigation systems. The EVE measurements, along with additional solar measurements from SDO and other satellite and ground-based instruments, will be used to advance our understanding of the solar EUV irradiance variability. For short time scales, EVE will make detailed observations on the evolution of flare events that are an important interest for space weather research...

Astronomische Nachrichten, 2003

The Coudé feed of the vacuum telescope (aperture D = 65 cm) at the Big Bear Solar Observatory (BB... more The Coudé feed of the vacuum telescope (aperture D = 65 cm) at the Big Bear Solar Observatory (BBSO) is currently completely remodelled to accommodate a correlation tracker and a high-order Adaptive Optics (AO) system. The AO system serves two imaging magnetograph systems located at a new optical laboratory on the observatory's 2 nd floor. The InfraRed Imaging Magnetograph (IRIM) is an innovative magnetograph system for near-infrared (NIR) observations in the wavelength region from 1.0 µm to 1.6 µm. The Visible-light Imaging Magnetograph (VIM) is basically a twin of IRIM for observations in the wavelength range from 550 nm to 700 nm. Both instruments were designed for high spatial and high temporal observations of the solar photosphere and chromosphere. Real-time data processing is an integral part of the instruments and will enhance BBSO's capabilities in monitoring solar activity and predicting and forecasting space weather.

Advances in Space Research, 2015

At the 10 th Thermospheric Ionospheric GEospheric Research (TIGER/COSPAR) symposium held in Mosco... more At the 10 th Thermospheric Ionospheric GEospheric Research (TIGER/COSPAR) symposium held in Moscow in 2014 the achievements from the start of TIGER in 1998 were summarized. During that period, great progress was made in measuring, understanding, and modeling the highly variable UV-Soft X-ray (XUV) solar spectral irradiance (SSI), and its effects on the

Launched on Feb. 11, 2010 on board the NASA Solar Dynamics Observatory (SDO), the Extreme ultravi... more Launched on Feb. 11, 2010 on board the NASA Solar Dynamics Observatory (SDO), the Extreme ultraviolet Variability Experiment (EVE) measures the solar EUV spectral irradiance from 0.1 nm to 105 nm at 0.1 nm spectral resolution and 10-second cadence. The data from EVE is useful for solar physics studies of solar irradiance variability and for space weather studies of the solar EUV as a primary driver for the Earth's upper atmosphere and ionosphere. EVE data products include a space weather product that is available within minutes of the measurements being taken, and a suite of more carefully calibrated irradiance data products available within a day. This paper will describe the EVE public data products and how the scientific community can access them.

A verified and updated version of the calibrated SOHO/CELIAS/SEM (absolute) solar extreme ultravi... more A verified and updated version of the calibrated SOHO/CELIAS/SEM (absolute) solar extreme ultraviolet (EUV) measurements from the beginning of the mission in 1996 through the present is available at the University of Southern California Space Sciences Center website. To complete this new version, six (1999- 2006) sounding rocket under-flights were analyzed using measurements from both a very stable Rare Gas

The Astrophysical Journal, 2007

Large solar energetic particle (SEP) events occur in association with fast coronal mass ejections... more Large solar energetic particle (SEP) events occur in association with fast coronal mass ejections (CMEs) and flares. We have studied in detail the rise phase of the SEP event of 1998 May 2 observed with the particle telescope ERNE aboard the Solar and Heliospheric Observatory (SoHO) spacecraft and ground based neutron monitors. Using the ERNE data and numerical modeling of the SEP transport, we present improved evaluations of the solar release profile of deka-MeV protons. The SoHO/EIT images are used to study the CME lift-off processes and possible sources of deka-MeV and hecto-MeV proton streams. In a first stage of the deka-MeV proton production, which starts not later than 4 min after the radio flash and the Moreton wave start, particles get accelerated from a few MeV through 20 MeV in ≈15 min. Both ERNE and neutron monitor data are used to study the release of solar protons in the hecto-MeV range. The proton acceleration to above 400 MeV was completed not later than 15 min after the onset of the eruption. Differences in the release scenarios, energy spectra, and composition of deka-MeV protons versus hecto-MeV protons suggest two different acceleration regions involved, perhaps situated on initially open lines and initially closed lines of coronal magnetic field. The first SEP productions were followed by a prolonged period of proton reacceleration, which continued in the ∼10-100 MeV range for more than 12 hours and during which a common energy spectrum was formed.

The Astrophysical Journal, 2007

Solar EUV and X-ray measurements from the Charge, Element and Isotope Analysis System/Solar EUV M... more Solar EUV and X-ray measurements from the Charge, Element and Isotope Analysis System/Solar EUV Monitor (CELIAS/SEM) on board Solar and Heliospheric Observatory (SOHO) and the Geostationary Operational Environmental Satellites (GOES) have been studied for four time periods. Two ultra-low-frequency CELIAS/SEM He II 30.4 nm pulsations were observed with frequencies of 0.02316+/-0.00232 and 0.00926+/-0.00232 mHz during days 244-248 of 1999 and

Solar Physics, 2011

The Extreme-ultraviolet Variability Experiment (EVE; see obtains continuous EUV spectra of the Su... more The Extreme-ultraviolet Variability Experiment (EVE; see obtains continuous EUV spectra of the Sun viewed as a star. Its primary objective is the characterization of solar spectral irradiance, but its sensitivity and stability make it extremely interesting for observations of variability on time scales down to the limit imposed by its basic 10 s sample interval. In this paper we characterize the Doppler sensitivity of the EVE data. We find that the 30.4 nm line of He II has a random Doppler error below 0.001 nm (1 pm, better than 10 km s −1 as a redshift), with ample stability to detect the orbital motion of its satellite, the Solar Dynamics Observatory (SDO). Solar flares also displace the spectrum, both because of Doppler shifts and because of EVE's optical layout, which (as with a slitless spectrograph) confuses position and wavelength. As a flare develops, the centroid of the line displays variations that reflect Doppler shifts and therefore flare dynamics. For the impulsive phase of the flare SOL2010-06-12, we find the line centroid to have a redshift of 16.8 ± 5.9 km s −1 relative to that of the flare gradual phase (statistical errors only). We find also that high-temperature lines, such as Fe XXIV 19.2 nm, have well-determined H.S. Hudson ( ) SSL,

The Astrophysical Journal Supplement Series, 2008

Advances in Space Research, 2002

Solar oscillations provide the most accurate measures of cycle dependent changes in the sun, and ... more Solar oscillations provide the most accurate measures of cycle dependent changes in the sun, and the Solar and Heliospheric Observatory/Michelson Doppler Imager (MDI) data are the most precise of all. They give us the opportunity to address the real challenge -connecting the MD1 seismic measures to observed characteristics of the dynamic sun. From inversions of the evolving MD1 data, one expects to determine the nature of the evolution, through the solar cycle, of the layers just beneath the sun's surface. Such inversions require one to guess the form of the causal perturbation -usually beginning with asking whether it is thermal or magnetic. Matters here are complicated because the inversion kernels for these two are quite similar, which means that we don't have much chance of disentangling them by inversion. However, since the perturbation lies very close to the solar surface, one can use synoptic data as an outer boundary condition to fix the choice. It turns out that magnetic and thermal synoptic signals are also quite similar. Thus, the most precise measure of the surface is required. We argue that the most precise synoptic data come from the Big Bear Solar Observatory (BBSO) Solar Disk Photometer (SDP). A preliminary analysis of these data implies a magnetic origin of the cycle-dependent sub-surface perturbation. However, we still need to do a more careful removal of the facular signal to determine the true thermal signal. Published by Elsevier Science Ltd on behalf of COSPAR.

The Extreme ultraviolet Variability Experiment (EVE) onboard Solar Dynamic Observatory (SDO), par... more The Extreme ultraviolet Variability Experiment (EVE) onboard Solar Dynamic Observatory (SDO), part of NASA's Living With the Star (LWS) program launched on 11 February 2010. Normal science operations began 1 May 2010 and have continued uninterrupted since then. The EVE instruments measure the solar extreme ultraviolet (EUV) irradiance from 0.1 to 105 nm with unprecedented spectral resolution (0.1 nm), temporal cadence (10 sec minimum), and accuracy (20% or better). Here, we present a review of the first year of EVE observations and initial science results presented at the LWS/SDO-1 Workshop held 1-5 May 2011 in Squaw Valley, CA. Much of the initial science from EVE has focused on the changes in the EUV irradiance due to solar flares. In the first eleven months of science operations, EVE observed over 350 C-class flares, 43 M-class flares, and 2 X-class flares. The location of a solar flare is important for understanding the EUV irradiance. ESP data is available in near-real time...

The Astrophysical Journal, 2011

ABSTRACT We report on the detection of oscillations in the corona in the frequency range correspo... more ABSTRACT We report on the detection of oscillations in the corona in the frequency range corresponding to five-minute acoustic modes of the Sun. The oscillations have been observed using soft X-ray measurements from the Extreme Ultraviolet Spectrophotometer (ESP) of the Extreme Ultraviolet Variability Experiment on board the Solar Dynamics Observatory. The ESP zeroth-order channel observes the Sun as a star without spatial resolution in the wavelength range of 0.1-7.0 nm (the energy range is 0.18-12.4 keV). The amplitude spectrum of the oscillations calculated from six-day time series shows a significant increase in the frequency range of 2-4 mHz. We interpret this increase as a response of the corona to solar acoustic (p) modes and attempt to identify p-mode frequencies among the strongest peaks. Due to strong variability of the amplitudes and frequencies of the five-minute oscillations in the corona, we study how the spectrum from two adjacent six-day time series combined together affects the number of peaks associated with the p-mode frequencies and their amplitudes. This study shows that five-minute oscillations of the Sun can be observed in the corona in variations of the soft X-ray emission. Further investigations of these oscillations may improve our understanding of the interaction of the oscillation modes with the solar atmosphere, and the interior-corona coupling, in general.

The Extreme ultraviolet Variability Experiment (EVE) aboard the NASA Solar Dynamics Observatory (... more The Extreme ultraviolet Variability Experiment (EVE) aboard the NASA Solar Dynamics Observatory (SDO) was launched on 11 February 2010. The EVE instruments measure the solar extreme ultraviolet (EUV) irradiance from 0.1 to 105 nm with unprecedented spectral resolution (0.1 nm), temporal cadence (10 sec minimum), and accuracy (20% or better). The highly variable solar EUV irradiance is a key measurement for the NASA Living With the Star (LWS) program as it is the major energy input into the Earth's upper atmosphere and thus impacts the geospace environment that affects satellite operations and communication and navigation systems. The EVE measurements, along with additional solar measurements from SDO and other satellite and ground-based instruments, will be used to advance our understanding of the solar EUV irradiance variability. For short time scales, EVE will make detailed observations on the evolution of flare events that are an important interest for space weather research...

Astronomische Nachrichten, 2003

The Coudé feed of the vacuum telescope (aperture D = 65 cm) at the Big Bear Solar Observatory (BB... more The Coudé feed of the vacuum telescope (aperture D = 65 cm) at the Big Bear Solar Observatory (BBSO) is currently completely remodelled to accommodate a correlation tracker and a high-order Adaptive Optics (AO) system. The AO system serves two imaging magnetograph systems located at a new optical laboratory on the observatory's 2 nd floor. The InfraRed Imaging Magnetograph (IRIM) is an innovative magnetograph system for near-infrared (NIR) observations in the wavelength region from 1.0 µm to 1.6 µm. The Visible-light Imaging Magnetograph (VIM) is basically a twin of IRIM for observations in the wavelength range from 550 nm to 700 nm. Both instruments were designed for high spatial and high temporal observations of the solar photosphere and chromosphere. Real-time data processing is an integral part of the instruments and will enhance BBSO's capabilities in monitoring solar activity and predicting and forecasting space weather.

Advances in Space Research, 2015

At the 10 th Thermospheric Ionospheric GEospheric Research (TIGER/COSPAR) symposium held in Mosco... more At the 10 th Thermospheric Ionospheric GEospheric Research (TIGER/COSPAR) symposium held in Moscow in 2014 the achievements from the start of TIGER in 1998 were summarized. During that period, great progress was made in measuring, understanding, and modeling the highly variable UV-Soft X-ray (XUV) solar spectral irradiance (SSI), and its effects on the

Launched on Feb. 11, 2010 on board the NASA Solar Dynamics Observatory (SDO), the Extreme ultravi... more Launched on Feb. 11, 2010 on board the NASA Solar Dynamics Observatory (SDO), the Extreme ultraviolet Variability Experiment (EVE) measures the solar EUV spectral irradiance from 0.1 nm to 105 nm at 0.1 nm spectral resolution and 10-second cadence. The data from EVE is useful for solar physics studies of solar irradiance variability and for space weather studies of the solar EUV as a primary driver for the Earth's upper atmosphere and ionosphere. EVE data products include a space weather product that is available within minutes of the measurements being taken, and a suite of more carefully calibrated irradiance data products available within a day. This paper will describe the EVE public data products and how the scientific community can access them.

A verified and updated version of the calibrated SOHO/CELIAS/SEM (absolute) solar extreme ultravi... more A verified and updated version of the calibrated SOHO/CELIAS/SEM (absolute) solar extreme ultraviolet (EUV) measurements from the beginning of the mission in 1996 through the present is available at the University of Southern California Space Sciences Center website. To complete this new version, six (1999- 2006) sounding rocket under-flights were analyzed using measurements from both a very stable Rare Gas

The Astrophysical Journal, 2007

Large solar energetic particle (SEP) events occur in association with fast coronal mass ejections... more Large solar energetic particle (SEP) events occur in association with fast coronal mass ejections (CMEs) and flares. We have studied in detail the rise phase of the SEP event of 1998 May 2 observed with the particle telescope ERNE aboard the Solar and Heliospheric Observatory (SoHO) spacecraft and ground based neutron monitors. Using the ERNE data and numerical modeling of the SEP transport, we present improved evaluations of the solar release profile of deka-MeV protons. The SoHO/EIT images are used to study the CME lift-off processes and possible sources of deka-MeV and hecto-MeV proton streams. In a first stage of the deka-MeV proton production, which starts not later than 4 min after the radio flash and the Moreton wave start, particles get accelerated from a few MeV through 20 MeV in ≈15 min. Both ERNE and neutron monitor data are used to study the release of solar protons in the hecto-MeV range. The proton acceleration to above 400 MeV was completed not later than 15 min after the onset of the eruption. Differences in the release scenarios, energy spectra, and composition of deka-MeV protons versus hecto-MeV protons suggest two different acceleration regions involved, perhaps situated on initially open lines and initially closed lines of coronal magnetic field. The first SEP productions were followed by a prolonged period of proton reacceleration, which continued in the ∼10-100 MeV range for more than 12 hours and during which a common energy spectrum was formed.

The Astrophysical Journal, 2007

Solar EUV and X-ray measurements from the Charge, Element and Isotope Analysis System/Solar EUV M... more Solar EUV and X-ray measurements from the Charge, Element and Isotope Analysis System/Solar EUV Monitor (CELIAS/SEM) on board Solar and Heliospheric Observatory (SOHO) and the Geostationary Operational Environmental Satellites (GOES) have been studied for four time periods. Two ultra-low-frequency CELIAS/SEM He II 30.4 nm pulsations were observed with frequencies of 0.02316+/-0.00232 and 0.00926+/-0.00232 mHz during days 244-248 of 1999 and

Solar Physics, 2011

The Extreme-ultraviolet Variability Experiment (EVE; see obtains continuous EUV spectra of the Su... more The Extreme-ultraviolet Variability Experiment (EVE; see obtains continuous EUV spectra of the Sun viewed as a star. Its primary objective is the characterization of solar spectral irradiance, but its sensitivity and stability make it extremely interesting for observations of variability on time scales down to the limit imposed by its basic 10 s sample interval. In this paper we characterize the Doppler sensitivity of the EVE data. We find that the 30.4 nm line of He II has a random Doppler error below 0.001 nm (1 pm, better than 10 km s −1 as a redshift), with ample stability to detect the orbital motion of its satellite, the Solar Dynamics Observatory (SDO). Solar flares also displace the spectrum, both because of Doppler shifts and because of EVE's optical layout, which (as with a slitless spectrograph) confuses position and wavelength. As a flare develops, the centroid of the line displays variations that reflect Doppler shifts and therefore flare dynamics. For the impulsive phase of the flare SOL2010-06-12, we find the line centroid to have a redshift of 16.8 ± 5.9 km s −1 relative to that of the flare gradual phase (statistical errors only). We find also that high-temperature lines, such as Fe XXIV 19.2 nm, have well-determined H.S. Hudson ( ) SSL,

The Astrophysical Journal Supplement Series, 2008

Advances in Space Research, 2002

Solar oscillations provide the most accurate measures of cycle dependent changes in the sun, and ... more Solar oscillations provide the most accurate measures of cycle dependent changes in the sun, and the Solar and Heliospheric Observatory/Michelson Doppler Imager (MDI) data are the most precise of all. They give us the opportunity to address the real challenge -connecting the MD1 seismic measures to observed characteristics of the dynamic sun. From inversions of the evolving MD1 data, one expects to determine the nature of the evolution, through the solar cycle, of the layers just beneath the sun's surface. Such inversions require one to guess the form of the causal perturbation -usually beginning with asking whether it is thermal or magnetic. Matters here are complicated because the inversion kernels for these two are quite similar, which means that we don't have much chance of disentangling them by inversion. However, since the perturbation lies very close to the solar surface, one can use synoptic data as an outer boundary condition to fix the choice. It turns out that magnetic and thermal synoptic signals are also quite similar. Thus, the most precise measure of the surface is required. We argue that the most precise synoptic data come from the Big Bear Solar Observatory (BBSO) Solar Disk Photometer (SDP). A preliminary analysis of these data implies a magnetic origin of the cycle-dependent sub-surface perturbation. However, we still need to do a more careful removal of the facular signal to determine the true thermal signal. Published by Elsevier Science Ltd on behalf of COSPAR.