C.1.4 Meteoroid streams

C.1.4.1. Meteor streams

Table C-2 gives the parameters for the main annual meteor streams. From these stream parameters fluxes are derived according to the method given in C.1.4.2_.

The meteoroid streams model is based on a method by N. McBride [RD.28] to derive meteoroid fluxes from meteor data. The present reference model uses data for 50 annual meteor streams as given by P. Jenniskens [RD.29]. These data were collected by a large number of observers over a 10 year period from observation sites in both the northern and southern hemispheres.

The meteoroid streams model given in C.1.4.2. is implemented in MASTER 2005 [RN.26] and in ESABASE2/DEBRIS [RD.30].

C.1.4.2. Meteor stream fluxes

The meteor stream geometry and activity at shower maximum is defined by:

• The solar longitude λ at shower maximum λ_max.

• The maximum zenithal hourly rate ZHR_max , which is the number of ‘visible’ meteors seen after various observer and location related corrections have been applied.

• Apparent radiant position in RA (right ascension of the radiant) and Dec (declination of the radiant) . These values are tabulated in Table C-2 at an epoch defined by the solar longitude λ⁰.

• The geocentric meteoroid speeds, defined as the final geocentric velocity V_∞ (in km s^-1) as the meteoroids reach the top of the atmosphere.

The right ascension of the radiant and for the declination for an instantaneous value of the solar longitude λ are obtained by

	(C-16)
	(C-17)

The shower activity as a function of time around its maximum is described by

(C-18)

where B is given in Table C-2 and describes the slopes of the activity profiles. Since most streams are found to have symmetrical profiles a single value of B is sufficient. The Geminids are the exception; this stream needs a different value of B for the inward and outward slope. Six of the streams do not have a strong enough ZHR to produce a slope, here a ‘typical’ value of B = 0,2 is used. Six other streams are best represented by the sum of 2 activity profiles, defined by a peak profile ZHR^p_max and B^p and a background profile ZHR^b_max with separate inward and outward slope values B^b+ and B^b- respectively. This results in the following expression:

(C-19)

The cumulative flux at solar longitude λ can now be expressed as:

(C-20)

with

(C-21)

The total particle flux F_TOT is obtained by summation over all streams

(C-22)

NOTE If the stream model is used in combination with the reference model of 10.2.3 it is considered that the model in 10.2.3 already includes the average yearly stream contribution.

C.1.4.3. Calculation of meteoroid stream fluxes

The following algorithm applies to determine the individual streams’ fluxes:

a. Given λ, choose the closest value of λ_max in Table C-2 and determine the stream number.

b. From Δλ = 2/B determine if λ is within the range (λ_max - Δλ) < λ < (λ_max+ Δλ) (Δλ determined by 1% of ZHR_max), if not, skip this stream (λ_max to be taken from Table C-2).

c. Calculate ZHR within the profile

(C-23)

d. For the six streams in Table C-2 which have two activity profiles (non vanishing B^b+ / B^b- values), calculate ZHR(λ) according to equation (C-19).

e. Form the ratio

(C-24)

f. The cumulative flux is now given by

(C-25)

with

(C-26)

or

(C-27)

k and α are obtained from Table C-2 according to the relevant stream number.

The arrival velocity V_∞ includes the gravitational corrections due to the Earth gravity.