# Presentation: 443349

## Objective:

- Create a high-fidelity synthesis of observations and theory to calculate the magnetic field in and near the magnetopause.  Such a calculation will be useful in:
-  studies of mechanisms for magnetic merging
-  input to numerical models of the magnetosphere
-  analysis of plasma data near and distant to merging sites
-  predictions of solar wind entry
***Primary science goal: ***
- Assess the degree of openness of the dayside magnetopause by comparing observations to predictions of anti-parallel and component merging.
***Secondary goals:***
- create a tool for prescribing the magnetic field at the magnetopause for use in data analysis and modeling
- provide a framework for the quantification and prediction of the solar wind flux across the magnetopause.

## Geomagnetic indices (DST)

**(e.g. Ace, Wind, Imp)**

**Geomagnetic indices (DST****)**

**Bow Shock and Magnetopause Location **
**(e.g. Shue et al., 1998; Farris and Russell, 1994)**

**Model of the geomagnetic field**** **
**(e.g. T96)**

**Estimation of magnetopause thickness **
**(e.g. Phan et al., 1996)**

**Calculation of projected IMF in the magnetosheath adjacent to magnetopause **
**(e.g. Cooling et al., 2001)**

**Theoretical calculation of magnetic field transition across magnetopause**** **
**(e.g. Cowley, 1995)**

**Database of magnetic field variation across the magnetopause in 4-D inc. transformed into boundary normal coordinate system**

**Flow-chart of the method for determining the variation of the magnetic field across the magnetopause**

## This approach was used in Chandler and Avanov [2003] to explain a Flux Transfer Event observed by POLAR at the dayside magnetopause under northward IMF  concluded to have been initiated by component merging at the dayside magnetopause.

**A similar technique was used in a survey of 52 magnetopause crossings made by POLAR at high latitudes in [*****Trattner et al., 2004*****], which showed 29 cases corresponded to anti-parallel reconnection, while the other 23 correspond to the component reconnection under similar solar wind conditions. **
**Some examples of shear angle distribution and merging magnetic field over dayside magnetopause for different IMF orientation are given. **

## Nominal location of the magnetopause (blue line) and location for 10% increased dynamic pressure (black line).

**Nominal location of the magnetopause (blue line) and location for 10% increased dynamic pressure (black line).**

## Slide 5

## Slide 6

## Slide 7

## Slide 8

## Slide 9

## Slide 10

| 

Date | 
Shear angle derived from T96-Cooling fields and B across the magnetopause, nT. |  | 
Defined Shear angle from POLAR measurements, and B across the magnetopause, nT. |  |
| --- | --- | --- | --- | --- |
| 
2000/03/19 | 
127O | Bx = -29 | 
140 O | Bx = -31 |
|  |  | By = -32 |  | By = -33 |
|  |  | Bz = 54 |  | Bz = 54 |
| 
2001/03/04 | 
144O | Bx = -46 | 
158O | Bx = -39 |
|  |  | By = -43 |  | By = -36 |
|  |  | Bz = 92 |  | Bz = 110 |
| 
2001/03/12 | 
152O | Bx = -30 | 
156O | Bx = -35 |
|  |  | By = -31 |  | By = -39 |
|  |  | Bz = 89 |  | Bz = 106 |
| 
2001/04/22 | 
168O | Bx = 6 | 
164O | Bx = 3 |
|  |  | By = 36 |  | By = 38 |
|  |  | Bz = 129 |  | Bz = 120 |

## The assumptions of component merging predict x-line is given by,

**The reversal of the magnetic field across the magnetopause occurs in the anti-parallel components only and is perpendicular to the X-line given by Eq.1. **
**The magnitude of the merging components is given by,**

**and**

**Where *****mline***** denotes the merging line.**

**(1)**

**(2)**

**(3)**

## It is possible that case of reconnection analyzed by Mozer et al., initiated by the component merging on April 1, 2001.

**Solar wind:**
**Bx=3, By=5, Bz=-5, N=4, V=810, Pd=8**

***It is possible that case of reconnection analyzed by Mozer et al., initiated by the component merging on April 1, 2001.***

**Shear angle between magnetosheath and magnetospheric field lines on the dayside magnetopause**

**Distribution of the magnitude of reconnected field, antiparallel case.**

**Distribution of the magnitude of reconnected field, assuming component reconnection.**

## Chandler and Avanov [2003] analyzed FTE observed by POLAR at the day side magnetopause initiated by the component merging. They found that merging components are ~ 20-30 nt. Distribution of magnitude of merging components coincides with the previous result.

**Bx=-5.5, By=5, Bz=12, N=32, V=300, Pd=7.5**

***Chandler and Avanov [2003] analyzed FTE observed by POLAR at the day side magnetopause initiated by the component merging. They found that merging components are ~ 20-30 nt. Distribution of magnitude of merging components coincides with the previous result.***

**Shear angle between magnetosheath and magnetospheric field lines on the dayside magnetopause**

**Distribution of the magnitude of reconnected field, assuming component reconnection.**

## Slide 14

## Conclusion

- Use of Cooling et al.[2001] model of the magnetosheath magnetic field and the T96 [1995] model for the magnetospheric field we are able to predict merging signatures at the magnetopause surface.
- Our results are in agreement with previous work (e.g Moore et al., 2002; Trattner et al., 2004) and extend these efforts.
-  Driving these two models with real upstream solar wind observations this automatic system can predict magnetic fields that are in reasonable agreement with those obtained from the direct measurements.
-  Comparisons with case studies show that component merging is  consistent with previous results.