# Presentation: 352409

## Plasma Vorticity inSaturnian Magnetosphere

- Daniel Morozoff
- Raymond Walker
- Steven Joy
- Joseph Mafi
- August 14, 2007
- PDS
- UCLA

## A Simulation of Saturnian Magnetic Dynamics

## The Spacecraft that have Shaped our Understanding of Saturn’s Dynamics

- Pioneer 11: Attaining Saturn in 1979, gave us the first true look at Saturn, with sufficient data to have some sort of understanding of the planet. It was only a flyby mission. Pioneer is in blue.
- The Voyager Spacecraft: In 1979 and 1980 Voyager 1 and 2 flew by Saturn respectively. The Voyager 1 and 2 trajectories are in black and green.
- Cassini : Arriving at Saturn in 2004, it sought to answer many of the questions left by Pioneer 11  and Voyager concerning Saturn.  The Cassini orbits are in red.

## Basis on Which Magnetic Rotations May Be Analyzed

- Frozen in Flux law : The magnetic flux in a moving flux tube is constant. This means that we can learn about the plasma motion by studying the changes in the magnetic field. The general equation reaches a simplified form of:
**                               ****V **= _(__**E × B**__)_
**                                          ****B** 2

## Basic Shape of  Saturn’s Magnetosphere

- Here is the basic shape for the
-            magnetosphere

##    Approach	

- 25 years ago Dr. Walker and Dr. Kivelson took a look at Pioneer 11 and found rotations in the magnetic field. We decided to start off  redoing the work with Pioneer 11 to confirm the results. More precisely we looked at the HVM instrument data stream and constructed a background magnetic field model for the magnetic behavior. We then examined the changes along the trajectory, confirming the previous results by Walker and Kivelson.

## Pioneer 11

-  The magnetic rotations

-  11 hour periodicity

**X****         **

**Y**

- Bx

- By

- Bz

- Bmag

## Analysis

- Once we completed work with the Pioneer 11 data, we began attempting to find similar rotations in the Cassini data.
- It was important to know when the spacecraft was inside the magnetosphere, for this is where we believe the rotations take place.
- The boundaries were located based on the raw data stream at 1 minute resolution. The results were compared with Steve Arridge’s magnetopause crossings .

## Locating Magnetopause Crossings

- Magnetopause

- Bow Shock

## Cassini Crossings

- Legend: Green- Magnetosphere  Blue- Magnetosheath
-               Red- Solar Wind  Yellow- Data Gap

- Crossings were fit by examining raw data.

## Dawn-Side Behavior with Cassini

- Probably not vorticity. Note 11 hour periodicity. Thought to be caused by plasma sheet motion over Cassini.
- Perhaps our initial ideas for Pioneer were false

**X**

**Y**

**Orbit 7**

- Bx

- By

- Bz

- Bmag

## Cassini Magnetic Dynamics

- Magnetic field rotations were found near the  dayside magnetopause.

**Y**

**X**

- Bx

- By

- Bz

- Bmag

## Magnetosphere Modeling

- Dayside rotations from the MHD simulation.

## Future Pursuits

- Continuing our research we seek to work with simulation models, and see how they are verified by the data we have observed.
- So far we have concluded that the behavior recorded by Pioneer 11 on the dawn-side was not vorticity, but most likely a current sheet crossing. Yet we have seen waves originating near the magnetopause on the day side.
-  We will continue examining the Cassini data as well as the ones produced by the Voyager spacecrafts. The source of the behavior we see having the 11 hours periodicity remains controversial.