MEETING OF THE METEOROLOGY PANEL (METP) METEOROLOGICAL INFORMATION AND SERVICE DEVELOPMENT WORKING GROUP (WG-MISD)

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1 METP-WG/MISD/1-IP/09 12/11/15 MEETING OF THE METEOROLOGY PANEL (METP) METEOROLOGICAL INFORMATION AND SERVICE DEVELOPMENT WORKING GROUP (WG-MISD) FIRST MEETING Washington DC, United States, 16 to 19 November 2015 Agenda Item 5: Matters Relating to WG-MISD Space Wx Work Stream 5.1: ConOps for Space Weather Information Services THE IMPORTANCE OF MONITORING EQUATORIAL PLASMA BUBBLES (Presented by Koichiro Kakihara) SUMMARY This document introduces the importance of monitoring Equatorial Plasma Bubbles (EPBs) for aviation. EPBs generation does not depend on short term solar activity, e.g., solar flare. The working group should consider the importance of EPBs on the impact to aviation and take it into consideration in the discussion of SWx definition. Action by the METP-WG/MISD Space Weather Work Stream is in paragraph INTRODUCTION Equatorial Plasma Bubble Equatorial Plasma Bubble (EPB) is a local ionospheric density depletion in the magnetic low-latitude ionosphere generated after the sunset. It has a longitudinal width of typically about 100km and a latitudinal extent of several thousands of kilometres. The ionospheric density inside the plasma bubble is typically 10 times less than that of the outside across the transition region from outside and inside with a typical width of a few tens kilometres. EPB often accompany small-scale plasma irregularities. Impacts of EPBs for aviation The large-scale ionospheric structure associated with EPB may cause extraordinary propagation of HF radio waves which may results in interference and/or fading in HF communications. The spatial change in density of the plasma cause spatial decorrelation in ionospheric delays (a few tens meters between outside and inside of an EPB) in GNSS signals to make the ionospheric delay correction by SBAS and GBAS difficult. Small-scale ionospheric irregularities cause scintillation in GNSS signals to degrade the (5 pages) MISD1-IP09_SpWx (Equatorial Plasma Bubbles)

2 METP-WG/MISD/1-IP/ measurement accuracy, and in the worst case result in lock-off of the signal. Degradation in GNSS measurements and loss of satellites not only degrades the positioning accuracy in air navigation, but would also have impact on other systems such as ADS-B, which depend on output of onboard GNSS receivers. Relation between the solar activity and the occurrence of EPBs Some works show that the occurrence of EPBs increase during high solar activity in 11-year solar cycle. (e.g., Gentile et al., 2004; Huang et al., 2002). In short term most of EPBs occurs irrespective of phenomena originating from explosive solar activities. Huang et al. (2001) has shown that most of EPBs occur during in low geomagnetic activity periods, though a very small part of EPBs is caused in severe magnetic storms. During the St. Patrick s event occurred on Marth 15, 2015 which is one of the largest space weather event in solar cycle 24, the occurrence of EPBs were suppressed (Tulasi et al., 2015). It is worth while noting that the occurrence also largely depends on seasons and longitudes (e.g., Tsunoda 1985, Nishioka et al., 2008). 2. DISCUSSION Importance of monitoring equatorial ionosphere as a part of space weather Because the occurrence of EPBs are not directly related to the solar flares, it is not enough to monitor only the solar event, but monitoring of the equatorial ionosphere itself is necessary. This fact is related to the definition of space weather in WMO space programme (2008). The present context in ConOps shows that the all space weather events are originated from the solar flares, however, EPB is not on the flow. The location of EPBs Because EPBs extend 50 to 200 km wide in the east-west direction and more than 3,000km long in the north-south direction whose center is on the magnetic equator (e.g.,. Wever et al., 1980). For monitoring these phenomenon, it should not put the boundary of regional sector on the magnetic (and geographic) equator. 3. ACTION BY THE METP-WG/MISD SPACE WX WORK STREAM The METP-WG/MISD Space Wx Work Stream is invited to: a) note the information contained in this paper, including the importance of EPBs and their impact to aviation, and b) consider describing EPBs in the space weather definition.

3 - 3 - METP-WG/MISD/1-IP/09 APPENDIX A Figure 1. Correlation between percent of EPB encounters by DMSP satellites and yearly averaged value of the F10.7 index during the past solar cycle (courtesy of Huang et al. 2002). Figure 2. (a) Number of EPB events encountered by DMSP satellites and (b) its occurrence rate as functions of the geomagnetic activity index (Kp) (courtesy of Huang et al., 2001).

4 METP-WG/MISD/1-IP/ Figure 3. Histograms showing monthly occurrence rate of EPBs from 2000 to 2006 detected by groundbased GNSS receiver networks (courtesy of Nishioka et al., 2008).

5 - 5 - METP-WG/MISD/1-IP/09 REFERENCES Gentile, L. C., W. J. Burke, and F. J. Rich, A climatology of equatorial plasma bubbles from DMSP , Radio Sci., 41, RS5S21, doi: /2005rs003340, C. Y. Huang, W. J. Burke, J. S. Machuzak, L. C. Gentile, and P. J. Sultan, DMSP observations of equatorial plasma bubbles in the topside ionosphere near solar maximum, J. Geosphys. Res., 106, A4, , Huang, C. Y., W. J. Burke, J. S. Machuzak, L. C. Gentile, and P. J. Sultan, Euqtorial plasma bubbles observed by DMSP satellites during a full solar cycle: Toward a global climatoloty, J. Geophys. Res., 107, A12, 1434, doi: /2002JA009452, Nishioka, M., A. Saito, and T. Tsugawa, Occurrence characteristics of plasma bubble derived from global groundbased GPS receiver networks, J. Geophys. Res., 113, A05301, doi: /2007JA012605, Tsunoda, R. T., Control of the seasonal and longitudinal occurrence of equatorial scintillations by the longitudinal gradient in integrated E region pedersen conductivity, J. Geophys. Res., 90(A1), , Weber, E. J., Buchau, J., and Moore, J. G., Airborne studies of equatorial F layer ionospheric irregularities, J. Geophys. Res., Vol. 85, pp , WMO space Programme SP-5, The potential Role of WMO in Space Weather, April END