Space Weather

sw_thumb Space weather generally refers to the changing environment between the Sun and Earth that arises due to changes in the sun's activity. A dramatic example is the generation of intense solar flares which greatly enhance the amount of X-ray radiation impinging on the Earth’s upper atmosphere. Most space weather effects of concern, however, arise from changes in the sun’s interplanetary magnetic field and the solar wind (mostly electrons and protons) embedded in this field. Such changes, at times, lead to a highly perturbed magnetosphere (to its particles and fields) and in turn to disturbances in lower regions. Energetic electrons and ions of magnetospheric origin can damage sensitive electronics on high orbiting spacecraft, harm astronauts, and through particle precipitation, produce color auroras and ionospheric disturbances including ionospheric currents. Ground induced currents arise from such currents in the upper atmosphere and can be a hazard to power grids. Ionospheric disturbances which include scintillations may alter or block signals leading to communication problems on aircraft flying polar routes, to disruption of Global Positioning System (GPS) services, and in general to systems relying on trans-ionospheric signal propagation. In general, solar storms leading to these effects typically reach Earth a day or two after the event and there is a need to better understand and predict their impacts.

CPI is an active member of the American Commercial Space Weather Association (ACSWA) and has decades of experience in developing first principles physics models relevant to the ionosphere, thermosphere, and auroral zone. This includes significant experience in working with solar data, energetic particle data, and remote sensing data. We have performed algorithm development for a variety of space weather satellite instruments (e.g., DMSP/SSUSI, TIMED/GUVI, and GOES-13/EUVS), sensor modeling, operational software engineering, as well as have calibration/validation (Cal/Val) experience (e.g., EUVS, DMSP, NPP) that is applicable to current and future solar EUV and particle sensors. These capabilities fall into four major areas.

Special Sensor Ultraviolet Spectrographic Imager (SSUSI)

SSUSI is a space-based remote sensing instrument with a spectrograph and imaging mode that was developed to measure emissions in the far ultraviolet (FUV). In imaging mode, SSUSI measures emission across the disk within five bands: Ly α [119 -124 nm], 130.4 [128-132 nm], 135.6 [134-137 nm], N2 Lyman Birge Hopfield LBHS [140-152 nm], and LBHL [165-180 nm].

CPI has been an active participant in each of the SSUSI calibration/validation programs (starting with the launches of F16 in 2004, F17 in 2006, and F18 in 2009). Work has focused on calibration and validation of dayside products and validation of auroral products. Calibration efforts have been directed to comparisons of SSUSI dayside data with TIMED/GUVI data and with radiances from CPI’s first-principals physics models. For F18, CPI has taken the lead on comparisons with coincident data from the Naval Research Laboratory’s (NRL’s) Special Sensor Ultraviolet Limb Imager (SSULI). Validation of dayside products has focused on comparisons of QEUV with independent solar measurements and of NmF2 and HmF2 with ground-based ionosonde data. Auroral validation efforts have been directed to comparisons of precipitation products (average energy Eavg and energy flux Q) with coincident data from SSJ/5 (on-board electron and proton particle sensors) and comparisons of NmE and HmE with incoherent scatter radar data.

ssusi1 figure

SSUSI F16 auroral images for two of the three spectral channels used to specify precipitation characteristics (the third channel is LBHS, shortward of the LBHL channel). Contours of constant solar zenith angle at 90° and 100° are displayed to identify nightside versus dayside observations.

Geostationary Operational Environmental Satellite (GOES) Extreme Ultraviolet Sensor (EUVS)

CPI and NRL physicists provided the first validation of the important new GOES EUV sensor, which provides energy fluxes in five bands. A contract was awarded by NOAA's Space Weather Prediction Center (SWPC) to NRL in October, 2006 followed by a 12-month effort to develop a calibration algorithm for the EUV Sensor (named EUVS) and conduct a validation of early on-orbit data. CPI physicists working closely with NRL solar physicists carried out the work, which was highly successful and led to encouragement by SWPC personnel to publish the work in spite of the focus being more operational rather than research based. The publication represents seminal research work on the early observations by this important sensor.

Project highlights included: early identification of a serious calibration error in EUVS data provided by SWPC, determination of its source, and the means to correct it; development of a calibration model with verification that it was performing as designed; completion of sensitivity studies addressing variations in cross-disk luminosity, pointing offsets, and changes in spectral shapes; demonstration of successful calibration through comparisons with independent measurements (done with four months of continuous EUVS data); and development of an algorithm for constructing flare and non-flare irradiance spectra from 2 to 80 nm using EUVS data from four of its five bands.

goes_euvs figure

The 5 December 2006 X9 flare recorded by GOES/EUVS channels A and E, and SORCE/XPS (after Evans et al., Solar Physics, 262, 2010). Inset: GOES-13 SXI image recorded at 10:44 UTC on 5 December 2006 (source: GOES Solar X-ray Imager, NOAA/NGDC). The bright horizontal band across the image evidences damage to 8 lines of pixels on the CCD.

Ionospheric Scintillation

CPI has extensive experience in ionosphere specification from dual frequency (L1 and L2) Global Positioning System (GPS) measurements (Reilly and Singh, 2004). We have devised a technique to combine both range and phase measurements to remove instrument-related variations, which are more prevalent in range measurements. Our standard methodology for ionosphere specification has been to solve for the effective sunspot number (SSNe) and simultaneously solve for biases using discrete inverse theory. We have developed software to compensate for ionospheric Faraday rotation effects for a passive microwave satellite (WindSat) in an operational mode (Singh and Bettenhausen, 2011). We have extensive experience in data acquisition as well as knowledge about the sensitivities and characteristics of various GPS receivers. We have developed software for better precision position from GPS system with augmentation from either differential GPS correction or atmospherically corrected differential corrections (Singh and Reilly, 2006).

We also have extensive experience in ionospheric irregularities at equatorial (Singh and Szuszczewicz, 1984) as well as high latitudes (Singh et al., 1985). Our research has not only focused on occurrence statistics, but also the cause-effect relationships with underlying physics phenomenon. We have experience in tropospheric delay determination and comparison with measurements from different instruments. The International GNSS Service (IGS) regularly provides zenith total tropospheric delay for over 100 GPS stations from all around the globe. We have studied almost one year’s worth of such data to estimate indirect delays from the troposphere.

ionosphere_gps figure

The effects of the ionosphere on GPS signals are illustrated. GPS signal refraction is caused by ionospheric irregularities that produce variations in signal group delay and phase advance. Signal diffraction is caused by ionospheric scattering of signals resulting in radio waves reaching receivers via multiple paths thereby causing fluctuations in signal amplitude and phase. Both refractive and diffractive effects on GPS signals are referred to as scintillation.

Joint Polar Satellite System (JPSS)

JPSS is the civilian component of the former joint civilian and military National Polar Orbiting Operational Environmental Satellite System (NPOESS) program. After the separation of NPOESS into its civilian and military portions, the National Oceanic and Atmospheric Administration (NOAA) assumed responsibility for the early afternoon orbit of the program which is now known as JPSS. The Department of Defense was given responsibility for the early morning orbit as the Defense Weather Satellite System (DWSS). The separate JPSS and DWSS programs continue to share the Common Ground System for satellite operation and data product processing. Data and imagery obtained from JPSS and DWSS will increase the timeliness and accuracy of public warnings and forecasts of weather events, and will also contribute to the climate data record and climate research. CPI has a small but key role in the development of the Integrated Data Processing Segment (IDPS) of the Common Ground System. CPI’s top contributions to NPOESS/JPSS include: assisting in the program office’s verification of the interfaces between the instruments and the ground data processing software; providing conceptual and technical leadership for the development of IDPS-specific software tools that make development, analysis and maintenance of IDPS algorithm codes much less expensive and time-consuming; providing conceptual and technical leadership for the integration of the IDPS software configuration management between the IDPS developer Raytheon Corp. and the government’s science team and calibration-validation support contractors.

NPP Satellite figure

The NPP satellite under development in a clean room at Ball Aerospace and Technologies Corporation. An earth-side view of the satellite is shown.

This description of our space weather capabilities can also be found in our Space Weather brochure.

References

Reilly, M. H. (2006), Ray trace calculation of ionospheric propagation at lower frequencies, Radio Sci., 41, RS5S37, doi:10.1029/2005RS003338.

Reilly, M. H., and M. Singh (2004), Electron density height profiles from GPS receiver data, Radio Sci., 39, RS1S16, doi:10.1029/2002RS002830.

Singh, M., and M. H. Reilly (2006), Improved positioning by addition of atmospheric corrections to local area differential GPS, Radio Sci., 41, RS5S29, doi:10.1029/2005RS003339.

Singh, M., and E. P. Szuszczewicz (1984), Composite equatorial spread F wave number spectra from medium to short wavelengths, J. Geophys. Res., 89(A4), 2313-2323, doi:10.1029/JA089iA04p02313.

Singh, M., P. Rodriguez, and E. P. Szuszczewicz (1985), Spectral classification of medium-scale high-latitude F region plasma density irregularities, J. Geophys. Res., 90(A7), 6525–6532, doi:10.1029/JA090iA07p06525.