Investigations of Global Space Weather with GPS

Transcription

1 Investigations of Global Space Weather with GPS A. J. Coster, J. Foster, F. Lind, P. Erickson MIT Haystack Observatory J. Semeter Boston University E. Yizengaw Boston College Overview Space weather can pose serious threats to space-based and land-based technological systems, and many of the serious space weather effects are produced by ionospheric storms. The global distribution of ionospheric sensors is severely lacking, especially over the oceans and in remote, difficult to access areas (Africa, some parts of Australia and South America.) Currently many questions remain about influence of longitude, the offset of the geomagnetic and geographic poles, and the South American Anomaly on the development of total electron content (TEC) gradients, enhancements, and depletions. Near real-time, globally distributed measurements of TEC and scintillation parameters are needed to provide a comprehensive picture of the mechanisms that drive major space weather effects. Space weather is just one piece of the larger, complex geospace system. The measurements described here will provide information about the larger geospace environment, and will support a systems perspective to geospace. I. Introduction The field of Space Weather studies the effect of short-term variations which occur on the Sun and in the solar wind and which result in changes in the behavior of the coupled ionosphere/thermosphere system. Space weather can pose serious threats to space-based and land-based technological systems. An example of this was described by Doherty et al., 2004, when, during the 2003 October 29th and October 30th ionospheric storms, there was no vertical navigation service in the FAA s Wide Area Augmentation Service (WAAS) coverage area for more than 11 hours on both days. Space weather effects include: an increase in the atmospheric drag on satellites; an increase in ionospheric scintillations (which can cause perturbations in navigational signals and communications); errors in GPS and in VLF navigational systems; loss in HF communications; electrical power blackouts due to damaging currents induced in power grids; and increased risk of radiation exposure to astronauts. Ionospheric storms in particular are closely associated with geomagnetic storms and, as described by Buonsanto [1999], represent an extreme form of Space Weather. Ionospheric storm phenomena that can introduce space weather effects include exceptionally large values of total electron content (TEC), which can introduce range errors; large spatial and temporal gradients in the TEC, which can introduce differential range errors; and small scale

2 density irregularities which can cause scintillation and/or loss of ability to track signals. An example of this is shown in Fig. 1, where the large TEC gradients associated with the 2003 November 20 ionospheric storm produced rapid variations of TEC which translated to large and rapidly changing range errors for GPS over both Washington, DC and Pittsburgh PA. Figure 1. Contour plot of Northeastern U.S.A. showing range errors due to ionospheric delay variations using GPS (courtesy of Mannucci, JPL/NASA) Many of the significant space weather events that have been reported are from N. American observations of storm enhanced density (SED) (Foster, 1993; Foster et al., 2002). Often associated with SED are large TEC gradients (Coster and Foster, 2007) and small-scale irregularities (Ledvina et al, 2002). One reason for the focus on North America is that during the last solar maximum ( ) only the US had a dense enough network of GPS receivers to fully view SED plumes. Recently, SED plumes have been reported in Europe (Yizengaw, et al., 2006) and in Japan (Maruyama, 2006). Many aspects of the SED feature appear to be magnetically conjugate (Foster and Rideout, 2006), although there is considerably less data coverage for observing such effects over the oceans and in the southern hemisphere (South America, Australia, and especially Africa). Space weather effects not associated with SED include the formation of many types of irregularities, including those associated with traveling ionospheric disturbances (TIDs) (Kelley and Fukao, 1991, Saito et al., 2002), midlatitude spread- F (Bowman, 1990), and other mechanisms. Solar radio bursts are another example of space weather. The Solar Radio Burst on December 6, 2006 produced a dramatic reduction in the reception of GPS signals on the sunlit side of the Earth during the 10 minutes associated with the peak of the radio burst (Cerruti, et al., 2008).

3 II. Science Questions As our society becomes increasingly dependent on technological systems such as the Global Positioning System (GPS), the ability to monitor and predict space weather in the near real-time is required. Certain critical applications such as railway control, highway traffic management, emergency response, commercial aviation, and marine navigation require high precision positioning. As a consequence, these applications require real-time knowledge of current and predicted space weather effects. To achieve this goal, a number of science questions need to be addressed. For example, what is the difference in the formation of SED in the different hemispheres and as a function of longitude? From analysis of the current data sets, there appears to be a preferential longitude for the formation of SED (Coster et al., 2007, Yizengaw et al., 2008) that may be related to the offset of the geographic and geomagnetic poles in the North American continent. Recent studies indicate that this offset has important consequences for the development of SED in the American sector (Foster and Coster, 2007). Another question is what is the influence of the South Atlantic Anomaly (SAA), an area of weakened geomagnetic field that lies over Brazil and part of the Atlantic Ocean, on the development and formation of space weather effects in both the American and African longitude sectors. Satellite observations (Hei et al., 2005) indicate that the ionosphere over Africa behaves very differently than the ionosphere over South America. III. Required Observations Currently global maps of TEC show large regions void of data over the oceans, even when COSMIC occultation data are included. This is illustrated in Figure 2, which represents an hour average of all TEC measurements from both the global network of GPS receivers and from COSMIC TEC measurements (represented by the letter C.) Areas of white indicate areas of no data in this figure. This lack of data makes global space weather prediction/interpretation difficult. Just from observing this figure, one can see an area over Florida of slightly increased TEC, during a nighttime period of 3:00-4:00 UT (22:00-23:00 LT). This also has a clear connection across the ocean to the enhancement shown at the western tip of Africa, which is in the post-midnight local time sector. Is this enhancement related to the physics associated with the SAA?

4 Figure 2. Global TEC map combining data from COSMIC and from the global network of GPS receivers for All data between 03:00:00-04:00:00 UT included. IV. Required Instrumentation To fully address the space weather problem, we should have the goal of real-time characterization of the global ionosphere as a standard product. This characterization will rely heavily on data from GPS measurements, but it will be enhanced by the real-time measurements from other sensors. To meet this goal, there is a requirement for real-time or near real-time observations from multiple platforms distributed uniformly over the globe. There is also a requirement to provide easy and open access to the data in standardized data formats and from easily identifiable and well-known data collection sites. Issues such as cost of instrumentation, power requirements, and connectivity must be addressed. These are all achievable within the next decade, especially with GNSS instrumentation such as GPS. The concept being described is that of Distributed Arrays of Small Instruments for Space Science (DASI). The last Decadal Survey of Solar and Space Physics (National Academy of Sciences, 2003) encouraged the deployment and utilization of distributed arrays of small instruments (DASI) to further space physics research. In recent years, GPS has become recognized as one of the premier remote sensing tools to monitor space weather events. By measuring the differential delay between GPS signals on two frequencies, the total electron content (TEC) can be measured along the line of sight between the receiver and the satellite. By combining TEC measurements from the worldwide receiver network, changes in the TEC distributions can be monitored along with the development of TEC gradients involved in serious space weather. In addition, by looking at TEC fluctuations, or by tracking the instances of loss of lock, GPS data can also be used to monitor ionospheric scintillation, another serious space weather phenomenon. In the last decade, considerable understanding of space weather phenomena has been achieved

5 by interpretation of global TEC maps. In a groundbreaking paper, Foster et al. [2002] linked narrow plumes seen in midlatitude GPS TEC observations as measured from the ground with plasmaspheric plumes as seen from 8 Earth radii by NASA's Imager for Magnetopause-to- Aurora Global Exploration (IMAGE) satellite. This last observation clearly demonstrated that a dense network of ground-based receivers can play a significant role in measuring the coupling between the ionosphere and the magnetosphere. A global network of GPS receivers can, and does, provide data that enables a system-science approach to the coupled, complex geospace system. Especially during large geomagnetic storms, single ground-based GPS receivers have a distinct advantage over satellite-based occultation systems such as COSMIC because no assumptions of uniform distribution are the made in analysis. Filling the gaps in TEC information over the oceans and over all of the continents (Africa, South America) will provide the necessary information to fully study space weather effects and to study the coupling between different atmospheric regions. Another example of how global networks of GPS receivers enable systemscience is demonstrated in the recently observed ionospheric signatures following sudden stratospheric warming events [Goncharenko, et al., 2010a; Goncharenko et al., 2010b]. This work provided clear evidence of the coupling between the stratosphere and the ionosphere. Global networks of GPS receivers can provide observations of travelling ionospheric disturbance associated with geomagnetic storms and tsunamis [Occhipinti, et al., 2008, Galvan, et al., 2010]. With GPS modernization, there are currently 8 GPS satellites broadcasting civilian signals on 2 or more frequencies. These new dual-frequency civilian signals enable ionospheric measurements on moving platforms for scientific purposes. This was very difficult to achieve prior to modernization. In addition, new low-cost, lower power GPS receivers are now available [Humphries, 2008; O Hanlon, 2009]. These low cost receivers can be used to augment data output from the African sub-continent and, when incorporated on low cost buoys, they can provide data over the oceans. In the future, additional GNSS signals such as GLONASS, COMPASS, and EGNOS can be incorporated into the receivers and used for analysis. Incorporating these new GNSS signals with GPS signals will provide higher accuracy and more reliable information in all environments. What is needed is a large global array of scientific instruments capable of providing high temporal and spatial information about the ionosphere in near real-time. New low-cost, lopower GPS receivers are available and can be made to work in the ocean environment and in remote hard to get to regions. V. Broader Impacts In addition to space weather information, the science products enabled by low-cost GPS receivers will lead to several direct societal benefits. High precision GPS positioning information on the oceans can be used to improve severe storm warnings and space weather forecasts, and to augment tsunami-warning systems. Offshore sea level measurements will allow us to determine the relative contributions of winds and waves to sea level variations and improve the existing storm surge models.

6 VI. Summary Society cannot become overly reliant on technology without an awareness and understanding of the effects of future space weather disruptions. As technology advances, societies of tomorrow are expected to only increase their need for highly accurate communication and navigation systems. These systems are vunerable to space weather and yet many of these systems are critical to our ability to respond to other emergencies. Most space weather effects are global in nature. For society to properly address them, real-time, global information will be required. To achieve these goals, problems that must be overcome include: Collecting space weather data over oceans and in remote, difficult to access locations Reliable and relatively inexpensive global communication links Real-time data transfer and access Establishment of open, free, easily accessible databases Data stored in standardized, common formats Regional TEC maps have provided a system-level understanding of many space weather effects. Regional TEC maps have also provided a deeper understanding of the coupling between different regions (the ionosphere and the magnetosphere; the ionosphere and the stratosphere). In the coming decade, the goal should be to provide global near-real time TEC maps.

7 VII. References Buonsanto, M.J. (1999): Ionospheric storms - A review. Space Sci. Reviews, 88, Cerruti, A. P., P. M. Kintner Jr., D. E. Gary, A. J. Mannucci, R. F. Meyer, P. Doherty, and A. J. Coster (2008), Effect of intense December 2006 solar radio bursts on GPS receivers, Space Weather, 6, S10D07, doi: /2007sw Doherty, P., A. Coster, and M. Murtagh (2004), Space weather effects of October November 2003, GPS Solutions, 8(4), 267, doi: /s Foster, J. C., Storm-Time Plasma Transport at Middle and HighLatitudes, J. Geophys. Res., 98, Foster, J. C., P. J. Erickson, A. J. Coster, J. Goldstein, and F. J. Rich (2002), Ionospheric signatures of plasmaspheric tails, Geophys. Res. Lett., 29(13), 1623, doi: /2002gl Coster, A. J., M. J. Colerico, J. C. Foster, W. Rideout, and F. Rich, (2007), Longitude sector comparisons of storm enhanced density, GRL, vol. 34 L18105, doi: /2007gl030682, Coster, A. and J. Foster, (2007), Space Weather Impacts of the Sub-Auroral Polarization Stream, The Radio Science Bulletin, No. 321 (June 2007). Galvan, D., A. Komjathy, M. P. Hickey, A. Mannucci (2010), Understanding Two Recent Tsunami Events Observed in the Ionosphere Using GPS Total Electron Content Measurements, J. Geophys. Res., Submitted September Goncharenko, L.P., A. J. Coster, J.L. Chau, and C.E. Valladares (2010): Impact of sudden stratospheric warmings on equatorial ionization anomaly. J. Geophys. Res., doi: /2010ja (in press). Goncharenko, L.P., J. L. Chau, H.-L. Liu, and A. J. Coster (2010): Unexpected connections between the stratosphere and ionosphere. Geophys. Res. Lett.,37, L10101, doi: /2010gl Hei, M. A., R. A. Heelis, and J. P. McClure (2005), Seasonal and longitudinal variation of largescale topside equatorial plasma depletions, J. Geophys. Res., 110, A12315, doi: /2005ja Humphreys, T.E., L. Young, and T. Pany, (2008), Considerations for future IGS receivers, 2008 IGS Workshop., International GNSS Service, Miami Beach, FL, Kelley and Fukao, M.C. Kelley and S. Fukao, Turbulent upwelling of the mid-latitude ionosphere, 2, Theoretical framework. Journal of Geophysical Research 96 (1991), pp Ledvina, B. M., J.J. Makela, and P.M. Kintner (2002), First Observations of Intense GPS L1 Amplitude Scintillations at Midlatitude, Geophys. Res. Lett., 29, doi: /2002gl Ledvina, B. M., J.J. Makela, and P.M. Kintner (2004), Temporal Scales of the GPS L1 Amplitude Scintillations at Midlatitude, Radio Science, 39, 1, doi: /2002rs Maruyama, T. (2006), Extreme enhancement in total electron content after sunset on 8 November 2004 and its connection with storm enhanced density, Geophys. Res. Lett., 33, doi: /2006gl027367, Art. No. L Occhipinti, G., A. Komjathy, and P. Lognonné (2008), Tsunami Detection by GPS, GPS World,

8 pp O'Hanlon, B.W., M. L. Psiaki, P. M. Kintner, Jr., and T. E. Humphreys, 2009, Development and field testing of a DSP-based dual-frequency software GPS receiver, in Proceedings of ION GNSS 2009, (Savannah, GA), Institute of Navigation. Saito A, Nishimura M, Yamamoto M, Fukao S, Tsugawa T, Otsuka Y, Miyazaki S, Kelly MC (2002) Observations of traveling ionospheric disturbances and 3-m scale irregularities in the nighttime F-region ionosphere with the MU radar and a GPS network. Earth Planets Space 54: Yizengaw, E., M. B. Moldwin, D. A. Galvan (2006), Ionospheric signatures of a plasmaspheric plume over Europe, Geophys. Res. Lett., 33, doi: /2006gl026597, Art. No. L Yizengaw, E., J. Dewar, J. MacNeil, M. B. Moldwin, D. Galvan, J. Sanny, D. Berube, and Bill Sandel (2008), The occurrence of Ionospheric Signatures of Plasmaspheric Plumes over Different Longitudinal Sectors, J. Geophys. Res., 113, A08318, doi: /2007ja