# The Sun and Space Weather
## 4 CMEs and Radio Bursts
Two sites of particle acceleration are indicated by ep..., one being the flare reconnection site underneath the flux rope and the other in the shock front at the leading edge of the flux rope. The gray ellipse at the core of the CME flux rope is the eruptive prominence. Heated plasma and accelerated particles from the flare site enter the flux rope. Accelerated electrons trapped in the flux rope cause moving type IV bursts. Accelerated particles from the flare site also flow down towards the Sun causing hard X-rays (by electrons), gamma rays (by protons), and neutron emission (due to proton interaction with the chromosphere). Sunward electrons trapped in flare loops produce microwave bursts and stationary type IV bursts. Energy deposited in the chromosphere by the flare particles results in chromospheric evaporation making the flare loops hot and emit soft X-rays. Thus, the type III burst corresponds to the flare impulsive phase when most nonthermal particles are accelerated at the flare site. Type II, Type III, and type IV bursts occurring at frequencies below the ionospheric cutoff (\(\sim\)15 MHz) are indicative of large-scale eruptions, as in Figure 10, and hence are highly relevant to space weather. Of these, type II bursts are due to shocks propagating away from the Sun, and the shock formation is indicated by the onset of metric type II bursts. Type II bursts also point to the small fraction of fast and wide CMEs relevant for space weather [75]. By tracking the type II bursts to tens of kHz, it is possible to predict their arrival time at Earth [76]. Some high-frequency bursts have been found to have direct effect on global positioning system receivers [77]. On 6 December 2006, a radio burst occurred with an unprecedented intensity of \(>\)10\({}^{6}\) solar flux units (sfu). The radio burst most severely affected the civilian dual frequency GPS receivers in the Sun-lit hemisphere. Typically, signals from four members of the global navigation satellite system (GNSS) are needed to be in view for a receiver to compute positioning. During the microwave burst, the number of satellites that could be tracked fell below four, and hence the positioning accuracy degraded significantly or was not even possible using the system for tens of minutes. A similar intense microwave burst occurred in SC 24 on 4 November 2015, with an intensity of \(\sim\)10\({}^{5}\) fst. During this event, signals from secondary air traffic control radars in Sweden, Norway, and Belgium became severely disturbed when the antennas were pointed in the direction of the Sun. Examination of the radio dynamic spectra reveals that solar radio flux dramatically increased near the L band at which the GNSS and radar signals are employed. There is also a lot of variability in the intensity of neighboring frequencies. [PERSON] et al. [78] have concluded that such high-intensity bursts belong to the \"dragon king\" type of events, in that the radio emission mechanism is different from that of regular events. The dragon king events are due to a coherent radio emission mechanism such as electron cyclotron maser, as opposed to gyro-synchrotron emission for regular bursts. X-ray photons during solar flares increase the ionization in the D and E layers of the ionosphere, thereby changing the conductivity. One of the consequences is the impact on the very low frequency (VLF) waves that bounce off from the bottom of the ionosphere. The amplitude and phase of the VLF waves are altered by the flare-induced changes in the ionospheric conductivity. By monitoring the VLF waves, one can detect solar flares of  
Figure 10: A solar eruptive event and the associated SOHO/LASCO CME (**a**), GOES soft X-ray flare of size M8.6 (**b**), and the radio bursts from the Radio and Plasma Waves experiment (WAVES) on board the Wind spacecraft (**c**). The shock in the CME image is responsible for the type II burst. The type IV burst is from the PEA. The large number of short duration bursts constitute the type III storm in (**c**).