CLASSIFICATIONS |
Classification of groups |
Classification of flares |
Groups of sunspots
Zurich or Waldmeier classification
A.- A simple pore or group of pores without bipolar configuration.
B.- Group of pores with bipolar configuration.
C.- Bipolar group in which one of the spots is surronded by a penumbra.
D.- Bipolar group whose two main spots have penumbra. At least one of them has a simple structure. Generally, the length of the group is <10º.
E.- Great bipolar group in which the two main sunspots have penumbra and, generally, a complex structure. Numerous smaller spots are among them.
F.- Very large bipolar or complex group. Length >15º.
G.- Great bipolar group without small spots between the main. Length>10º.
H.- Unipolar spot with penumbra. Diameter >2º,5.
I.- Unipolar spot with penumbra. Diameter <2º,5.
This classification uses two criteria: the aspect and the size of the group, and allows to describe its morphology and its evolution. However, the classification can be only approximated because of several factors: there are some ambiguities in the definitions, and we would need to measure the distances with enough precision. Also, there is a fundamental ambiguity that affects all our solar observations: the notion of "group of sunspots", specially when the same region presents several groups nearby one another. And don’t forget that we are trying to include in 9 different classes an almost infinite variety of groups, and that means that the more rigorous and precise we want to be, the more exceptions we are going to find.
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This classification, used from 1990, is an extension of the system of Waldmeier. It uses a 3 -letter code:
1st letter.- It is the same as in the Waldmeier classification, with two exceptions: G and I are suppressed. Groups G are classified like C, D or E, whereas H includes the unipolar groups with penumbra, regardless of their size.
2nd letter.- It describes the appearance and size of the main sunspot in the group:
x.- Without penumbra.
r.- Rudimentary penumbra, with irregular edges and usually brighter than a normal penumbra.
s.- Symmetrical penumbra, almost circular and with radial filaments. Diameter < 2.5 heliographic degrees.
a.- Asymmetric or complex penumbra. Diameter < 2.5 heliographic degrees.
h.- Just like “s” but with diameter > 2.5 heliographic degrees.
k.- Just like “a” but with diameter > 2.5 heliographic degrees measured in the direction N-S.
3rd letter.- It describes the distribution of the sunspots in the group:
x.- Individual spot.
o.- Open distribution. No sunspot in the central zone of the group.
i.- Intermediate distribution. Some sunspots in the central zone of the group.
c.- Compact distribution. Great sunspots in the central zone. At least one of them has penumbra. Sometimes, all the sunspots are surrounded by only one penumbra.
The Mc Intosh classification allows to describe the morphology of a group with more precision than the system of Waldmeier, but by eliminating the classes G and I, do not have the evolutionary nature of the first one.
This classification refers to the distribution of magnetic polarities in a group.
Alfa.- Unipolar group with one or more sunspots of the same polarity.
Beta.- Bipolar group. The change of polarity is well marked and generally occurs near the center of the group.
Gamma.- Complex group with an irregular distribution of the polarities.
Beta-gamma.-Bipolar group without a well marked division between the two polarities.
Delta.- Group with opposed polarities within the same penumbra.
In addition the suffixes p and f are used when the western or eastern sunspot, respectively, is dominant.
Delta represents a very special magnetic configuration that can affect to a whole group or be restricted to an area of the same. The Delta is present in the most active groups that we can observe in the Sun.
Flares
X - Rays
This classification uses the peak flow (f) of x-rays emitted.
B.- f < 10^-6 W/m2
C.- 10^-6 < f < 10^-5 W/m2
M.- 10^-5 < f < 10^-4 W/m2
X.- f > 10^-4 W/m2
In turn, each one of these classes has 9 subdivisions indicating the intensity of flow wihtin each interval. Thus, by example, a M6 flare indicates a flow of 6·10^-5 W/m2. The X flares could cause intense magnetic and radio storms, and disrupt the communications in our planet.
Optical classification
Here, we consider the extension achieved (in millionths of hemisphere) and the observed brightness.
s.- <100 millionths
1.- 100-250 millionths
2.- 250-600 millionths
3.- 600-1200 millionths
4.- >1200 millionths
A letter is added to each class of area to indicate its brightness: F=Weak, N=Normal, B=Brilliant. 4B would be the most important flares.
Radio storms
I.- Brief pulses (300-50 MHz) superimposed on a background of continuous emission.
II.- Pulses of great intensity starting in the 300 MHz and move towards 10 MHz. Associated with flares and with the movement of the shock wave that raises by the corona at speeds from 1000 to 15000 Km/s.
III.- Pulses that move rapidly between 500 and 0,5 MHz. Associated with electron currents moving about 100000 Km/s. Most often they are associate with active regions.
IV.- Continuous emission between 300 and 30 MHz. Associated also with the flares and with material moving at 1000 Km/s.
V.- Similar to type III but later.
Geomagnetic storms
To estimate the intensity of a geomagnetic storm, an index (K) is used which measures the deviations of the Earth magnetic field with respect to an average curve for each location of observation. An index derived from this one is the so-called Kp, which is an average of K calculated each three hours based on severals stations distributed around the world. Other indexes used are merely variations on the same subject.
A scale (NOAA) is defined by basing on the values of Kp, and it describes the intensity of a storm and its effects (the mentioned latitudes are magnetic not geographic):
G1.- Minor storm (Kp = 5). Aurora visible at high latitudes. Minor fluctuations in power grids.
G2.- Moderate storm (Kp = 6). Aurora visible at 55º latitude. Alterations in the electrical systems located at high latitudes.
G3.- Intense storm (Kp = 7). Aurora visible at 50º latitude. Disturbances in the radio waves.
G4.- Severe storm (Kp = 8). Aurora visible at 45º latitude. Strong disturbances in the transmissions of high/low frequency. Overloads in the high-voltage lines. Problems with the orientation of the satellites.
G5.- Extreme storm (Kp = 9). Aurora visible at 40º latitude. Transmissions of high/low frequency impossible. Collapse in the telecommunications. Widespread problems in the electrical grid. Damages to the transformers.
