# Presentation: 863240

## Coronal Mass Ejections of Solar  Cycle 23

- Nat Gopalswamy (NASA/GSFC)
- September 12,  2003
- SEC seminar

**Notes:**
Tousey et al. (1974) used OSO-7 data (Nov 1971 to May 1973 – 19.5 mo) to estimate a rate of 14 CMEs per month (0.5 CMEs/day). OSO –7 had observed 23 CMEs in all.
Skylab observed  110 CMEs during its 227 days of observations. Hildner et al. (1976) estimated a rate of 30 CMEs per day (1 a day). They also compared the CME rate with sunspot number and obtained a correlation coefficient of 0.67 and a regression line rate = 0.96+.084N (based on 7 rotations). During maximum 3.2 per day (100 per month would be expected based on this relation). Detailed investigation of CME rates by combining all the available data on CMEs from Skylab, SMM/CP, P78-1/Solwind was performed by Webb and Howard (1994) including correction for the visibility function. The long-term averaged CME rate obtained by them was in line with the prediction of Hildner et al. (1976).  Similar results were also obtained by Cliver et al (1994) with short-tem averaging over the Carrington Rotation period. 

Figure 1 shows the solar corona during the minimum and maximum of the current solar cycle. The minimum corona is characterized by the equatorial streamer belt, while the maximum corona has streamer structures all over the Sun. The coronal structures essentially reflect the latitudinal excursions of the source surface neutral line in the two phases. Since coronal mass ejections occur from closed magnetic field regions, one expect a corresponding change in the distribution of source regions of the CMEs on the Sun. Figure 2 shows the X-ray images of the corona taken on the same days as in Fig. 1. The distribution of the bright regions on the Sun again reflect the distribution of closed filed regions on the Sun, primarily belonging to one class, viz. active regions. Filament regions is another kind of closed field regions from which CMEs  originate. The spatial distribution of filament and active region sources  have different dependences on the solar activity cycle and accordingly the associated CMEs are also expected to have different behavior with the solar cycle. In this paper, we present preliminary results on the variability of properties of CMEs with the progression of the current solar cycle (23). 
In particular, we consider CME rate, their mean and median speeds and how these quantities correlate with other tracers of solar activity cycle such as the sunspot number and tilt angle. The poles of the Sun changed their polarity around the maximum of the current cycle. This process coincides with the “rush-to-the-poles” phenomenon of the polar crown filaments (PCF). The southern and northern poles of changed their magnetic polarity at different times and we show that this asymmetry is also reflected in the rate of CMEs and prominence eruptions. We also consider another special population of energetic CMEs, which are different from the prominence associated CMEs. These energetic CMEs are important from the point of view of geoeffectiveness.  We compare the rate of the fast and wide CMEs with that of IP shocks, interplanetary type II bursts and large solar energetic particles (SEPs). This comparison revealed that only a small fraction of the CMEs is capable of having large impacts on the geospace. 

## Thanks to...

- The LASCO team
- LASCO operations scientists who produced preliminary lists of CMEs (O. C. St. Cyr, S. P. Plunkett, G. Lawrence)
- The CME catalog team (E. Aguilar-Rodriguez, G. Michalek, S. Nunes, N. Rich, A. Rosas, G. Stenborg, S. Yashiro)
- Collaborators: A. Lara, R. Howard, M. Shimojo, K. Shibasaki

## In this talk...

- CME rate (daily rate averaged over Carrington Rotation for the years 1996-2002)
- CME rate and other measures of solar activity (Sunspot number, tilt angle, prominence eruption, polar field strength)
- CME rate and polarity reversal
- Summary
- Will not talk about Special Populations (Halos, FW) – http://cdaw.gsfc.nasa.gov/publications

**Notes:**
Data sources:
The primary data for this study came from the Solar and Heliospheric Observatory (SOHO) mission’s Large Angle and Spectrometric Coronagraph (LASCO), which images the corona from about 1.5 Rs to 32 Rs since the beginning of 1996. The study period extends to the end 2002, when the solar activity for the current cycle has passed the maximum. 

## Data Sources

- CMEs form the SOHO/LASCO catalog: _[http://cdaw.gsfc.nasa.gov/CME-list](http://cdaw.gsfc.nasa.gov/CME-list)_
- Tilt angle from
-      _[http://quake.stanford.edu/~wso/Tilts.html](http://quake.stanford.edu/~wso/Tilts.html)_
- KPNO magnetic field data
- Prominence Eruption data from the Nobeyama Radioheliograph catalog:
-     _[http://solar.nro.nao.ac.jp](http://solar.nro.nao.ac.jp/)_

## CMEs at minimum and maximum phases: CMEs occur from closed field regions

- Minimum: 1 CME

- Maximum:12 CMEs

## Soft X-ray Corona

- Minimum

- Maximum

## SOHO CMEs: Annual Distributions 

- 204

- 351

- 697

- 957  1577 1483 1637

- 1996-2002

- #

- 1998 – 3-month gap
- 1999 – 1-month gap
- Highest # & speed in 2002

-   WIDTH                SPEED

**Notes:**
Overview of CME properties
Fig 3 shows the number of CMEs observed in each year since 1996. The number in each bin corresponds to the actual number of observed CMEs, which might differ substantially if there are data gaps. The major data gaps occurred in 1998 when SOHO mission was interrupted from June 24 to October 15. There was also another gap of one month in January 1999. In spite of these gaps, we note that the number of CMEs per year is much larger than those reported by earlier coronagraphs at the corresponding phases of the previous solar cycles. The number of CMEs conserved in 2002 alone substantially is similar to the number of CMEs observed during the entire mission life time of SMM (1206) and  P78-1 (1607) coronagraphs. The substantial increase in the number can be attributed to the increased sensitivity of the LASCO, which has a dynamic range of 6000, compared to 40 and 30 fro the SMM and P78-1 coronagraphs. The substantially large field of view also contributes to the higher number of CMEs detected.  We also note several additional features in the annual distribution: The CME number drops from a high value of 1535 in year 2000 to 1412 in 2001 (8% drop) and then goes back up to the largest value (1584, 12% increase) for the cycle in 2002.

## All CMEs (1996-2002)

-  Averaged over Carrington Rotation period (27.34 days)
-  CMEs/day increased from
- 1 every other day to > 6 per day
- SOHO CME rate is much larger than pre-SOHO rates

- Td = Down time (days) in each CR
- Tu = Up time (days) during each CR
- Rmax = Max no. of CMEs per
- day during a CR
- Robs = # CMEs in the CR/Tu
- Upper limit to rate:
-  (Tu Robs + TdRmax)/27.34
- Lower limit**:**** **TuRobs/27.34

- Max rate from pre-SOHO data

- St.Cyr et al
- 2000

**Notes:**
CME rate averaged over Carrington Rotation periods is given in Fig. 4. Note that the CME rate increased from less than 1 during solar minimum in 1996 to slightly more than 6 in 2001. What is plotted is the observed CME rate (Robs), which is simply the number of CMEs in a CR divided by the SOHO up-time (Tu, measured in days)  during that CR. The error bars have been computed on the basis of down times (Td) exceeding 3 h in each rotation period. If Rmax is the maximum number of CMEs observed on any one day in a given given CR, then we assume that CMEs occurred Rmax during Td (measured in days) to compute the upper limit to the rate as  (Tu Robs + TdRmax)/27.34. The lower limit to the rate is obtained by assuming that the CMEs occurred at the observed rate during the down time: Robs/27.34. The maximum rate for the current cycle occurred in 2002, after the solar maximum. The rate during solar maximum is much higher than that reported for previous cycles (Webb and Howard, 1994; Cliver et al., 1994; MacQueen et al., 1999). The CME rate obviously has some cyclical behavior, which needs further investigation (see Ivanov and Obridko, 2000 for such behavior during previous cycles). It is possible that some head-on narrow CMEs may have been missed by LASCO. A correction may be required as a visibility function (Webb and Howard, 1994). However, initial analysis by St. Cyr  et al. (2000) suggests that such a correction may not be necessary for the LASCO data.  

## Speed Variability:  Solwind & SMM 

- • “speeds vary widely, even when averaged over intervals as long as a year.”  Hundhausen (1999)
- •  Webb (1994): Solwind data shows solar cycle  variability of CME speed; SMM does not.
- •  The 1985 SMM point may not  be reliable :
-  only 39 of the  62 CMEs had speed measurements. Highest annual average from the entire  SMM epoch (458 km/s)
- • Solwind average speed is much  smaller.
- • Apart from this point, the annual average of mean  and median speed show solar cycle variation.
- • Ivanov & Obridko (2000) : Semiannual
-  averages of mean speed show a peak near minimum, in addition to the peaks in the maximum epoch (1981-1982, 1989)

- 1980-1989 data   from St. Cyr et al. (1999)
- 1979 data from Solwind catalog.

**Notes:**
Variability of CME Speed
Early assessment of the Solwind CME speeds indicated that the mean CME speeds increased towards solar maximum, although the SMM data did not indicate such a variation (Webb, 1994). In fact Hundhausen (1999) remarked that the “speeds vary widely, even when averaged over intervals as long as a year.”  In Fig. 6 we have plotted the annual averages of CME speeds obtained by the Solwind and SMM coronagraphs. The speed values were taken from St. Cyr et al. (1999) for 1980 to 1989. For the year 1979, we computed the average speed from the Solwind CME catalog (hhtp://). Notice that both Solwind and SMM data points show a higher rate for the maximum. The Solwind data also indicate a low rate for solar minimum. The mean speed obtained from the SMM data for year 1985 is anomalously high in contrast to the Solwind value.  Examination of the SMM CME catalog (St Cyr and Burkpile, 1993) indicates that it was not possible to measure the measure the speeds of more than 40% of the CMEs (only 39 of the 62 CMEs had speeds). On the contrary, Solwind detected the same number of CMEs (not the same CMEs) that resulted in a mean speed of only 150 km/s. On the other hand the SMM speed in 1985 (458 km/s) was the highest annual average from the entire SMM epoch (Hundhausen, 1999). The median speed, however, behaved reasonably.  By combining the SMM and Solwind data, Ivanov and Obridko (2000) found that the semiannual averages of mean speed showed a peak near minimum (1985), in addition to the peaks in the maximum epoch (1981-1982, 1989). 

## CME speed also increases from Min to Max

## CME Rate & Sunspot Number

- Hildner et al. (1976) had predicted a peak rate of 3.2 CMEs/day based on Skylab data
- Webb & Howard (1994), Cliver et al. (1994) confirmed this relationship using all available data (1973-1989)
- SOHO data confirms the relationship, but the slope is drastically different, because the peak rate nearly doubled.
- Large scatter for large SSN: Correlation weakens during solar maximum phase

**Notes:**
CME Rate & Sunspot Number:
Based on the 110 CMEs observed by Skylab over a period of 227 days,  Hildner et al. (1976) found that the CME rate (R) was correlated with the sunspot number (N) and obtained the relation, R = 0.96+.084N (based on 7 rotations). They suggested that this relation is independent of the phase of the solar activity cycle and predicted a rate 3.2 per day (100 per month) for solar maxima. With more and more observations coming in from Solwind and SMM/CP data this relation was essentially confirmed (Webb & Howard, 1994; Cliver et al., 1994). SOHO/LASCO data also shows a good correlation (r=0.89), but the slope of the regression line is significantly different from the previous ones. We attribute this primarily to the better sensitivity of the LASCO coronagraphs and the enormous dynamic range(~6000 compared to 30 for Solwind and 40 for SMM). Additional factors include larger field of view and more uniform coverage over long periods of time. 
The correlation appears to be slightly weakened for higher (>90) sunspot numbers, beginning in 1999. Sunspots occur in active regions, so the correlation between CME rate and solar activity should be good only for those CMEs that originate from active regions. It is well known that the phenomenon of rush to the poles starts before the maximum and somewhere during the maximum. No sunspots are associated with the polar crown filaments, so the CMEs associated wi8th the eruption of the PCFs have nothing to do with the sunspot activity. Therefore, we need to investigate the solar cycle variation of prominence eruptions and the CMEs associated with them. 

## CME Rate and Prominence Eruptions

- Prominence eruptions from the Nobeyama Radioheliograph (automatic detection)
- Only limb events
- Ground-based: only 8h/day

**Notes:**
CME Rate and Prominence Eruptions
The Nobeyama radioheliograph images the Sun in microwaves at 17 and 34 GHz for 8 h each day since 1992. Since prominences are cool material (~800 K), they are optically thick in microwaves and hence can be readily imaged (see, e.g. Gopalswamy, 1999). Recently, Gopalswamy et al. (2003) studied the association between prominence eruptions detected automatically from the NoRH images. They found that most of the filament eruptions were associated with CMEs. We extended that study to include the prominence eruptions in 2002.  Fig. shows the correlation between the prominence number in each Carrington Rotation and the number of CMEs in that rotation. There is clear correlation, but somewhat weaker than that between CME rate and sunspot number. This is expected because the majority of CMEs originate from active regions. 

## CMEs & Prominences

- High latitude (HL) prominence eruptions and CMEs during CR 1950-1990 (mid ’99 – early ’02)
- N-S asymmetry (NHL ends in 11/00; SHL ends in 5/02)
- These CMEs are not associated with sunspot activity

**Notes:**
In order to see how the CMEs associated with prominence eruptions affect the correlation between CME rate and sunspot number, we have plotted the latitude of prominence eruptions and the associated CMEs as a function of Carrington Rotation number in Fig. 5. We see a general spreading of the CME and PE latitudes attaining a latitude of 60 deg by year 1999. Starting CR 1953 (second half of year 1999) both CMEs and PEs occurred at high southern latitudes until about CR 1990 (first half of year 2002). There is also a clear north-south asymmetry in the number and time of high-latitude (>60 deg) eruptions. Clearly, this is related to the rush to the pole phenomenon and the subsequent polarity change during the maximum of cycle 23. 

## Tilt Angle, CMEs & PEs

- High latitude CMEs and prominence eruptions occur when the tilt angle is large (~ 50 deg)
- CMEs seem to follow the tilt angle better than the PEs do.

**Notes:**
Tilt Angle, CMEs & PEs
One way of looking at the spreading of CME and PE activity to higher latitudes is to compare with the maximum excursion of the source-surface neutral line. The tilt angle is defied as the maximum extent of the heliospheric current sheet (HCS) and is computed by applying a potential field model to photospheric magnetic field observations. Fig. 6 shows the maximum northern and southern extent and the the average value  of the tilt angle with the locations of the CMEs and PEs superposed. We see that the tilt angle curve serves as a rough envelope of the PE and CME  locations. The relation is much closer for CMEs than for the PEs. The deviations during solar maximum may not be significant because the tilt angle above 70 deg are lower limits.  The sharp decline in tilt angle in the beginning of year 2001 clearly has corresponding shift in the locations of CMEs and PEs. 

## CME Rate as a function of Tilt Angle

- Increasing tilt: CME rate is positively correlated with TA (r = 0.80)
- Max Phase: TA > 50 deg, CME rate weakly correlated with TA (r = 0.46)
- Declining Phase: CME rate not correlated with TA (r = -0.02)
- (Rush to the poles: Cliver et al. 1994)

**Notes:**
CME Rate as a function of Tilt Angle
The CME rate and the tilt angle are compared as a function of time in Fig. 7. Following Cliver et al. (1994), we considered 50-degree tilt angle to be critical value, which roughly separates the minimum and maximum conditions. We can distinguish between three intervals based on the value of the tilt angle: (i) the rise phase from 1996 to middle of 1999, (ii) the maximum phase from middle 1999 to  beginning of 2001, and (iii) the declining phase starting in early 2001. While there is an overall correlation between CME rate and tilt angle, there are large deviations from the regression line. The correlation is rather good for the rise phase (r=0.83). During the maximum and declining phases  the correlation is rather weak (r=0.24, and –0.31, respectively), but has the right trend.

## CME Rate & SSN

- SSN has double peak (largest in July 2000)
- CME rate peaked in Oct 2002
- The difference persists when smoothed over 5, 7, or 13 rotations

- 5 Rot

- 7 Rot

- 13 Rot

## SSN & CME Rates

- SSN: Sunspot number; Total: All CMEs; LL-low-latitude CMEs; HL – high-latitude CMEs
- Red arrow: reversal at North Pole; Blue arrow: reversal at South Pole

## W

- E

- N

- S

- +++++

- -    -   -   -

- + +  +  +

- -   -  - -

- + + + + +

- -   -   -  -

- PCF

## Polarity Reversal in Photospheric Field

## Cycle 23

- HL Rate picks up when polar B declines
- North polar reversal at the time of cessation of NHL CMEs
- South polar reversal 1.5 yr later, again coinciding with the cessation of SHL CMEs
- LL CME rate rather flat after a step-like increase
- Consistent with the time of PCF disappearance

- Arrows: Lorenc  et al. 2003;  Harvey & Recely, 2003;  Gopalswamy et al., 2003

## Cycle 21

- Solwind coronagraph on board P78-1 (corrected rates published by Cliver et al., 1994)
- PCF: Webb et al. 1984; Lorenc et al. 2003
- KPNO mag data
- CME cessation coincides with the polarity reversal

## When are the reversals?

- HL streamer peak (Feb 2000) implies presence of HL closed structures.  reversal is not complete
- HL streamer brightness declines significantly towards the end of 2000 – agrees with CME cessation

- Wang, Sheeley & Andrews, 2002

## A High-latitude CME & PCF

- Nobeyama Radio Prominence

- LASCO/C2

## Energy involved in CMEs

- M = 8.1015 g
- V=733 km/s
- KE = 2.1031 erg
- It takes about 1200 CMEs over a period of 3 years to complete the polarity reversal
- (2.1031 erg/day is dissipated)

## Summary

- CME rate increases by an order of magnitude from min (0.5/day) to max (6/day)
- Max rate is almost twice the rates estimated for previous cycles
- Speed increases by a factor of ~2. This was not conclusive from pre-SOHO data. Now it is firmly establishd.
- Sunspot activity peaks in Jul 2000; CME activity peaks in Oct 2002
- Smoothed data show both sunspot and CME activity with a double peak. The first of the sunspot peak and the second of the CME peak are the largest. The second (largest) CME peak is also delayed with respect to the second sunspot peak.
- Correlation between SSN & CME activities can be better understood by separating high and low-latitude CMEs.
- The difference between sunspot activity and CME activity is due to the high-latitude CMEs, which are not associated with sunspots, but with polar crown filaments.
- Cessation of high-latitude CMEs and prominence eruptions are good indicators of polarity reversal including the north-south asymmetry in reversal
- CMEs may be the mechanism by which polarity reverses and involves dissipation of ~2.1031 erg/day