MAGNETIC RECONNECTION IS ARGUABLY ONE OF THE MOST IMPORTANT ENERGY CONVERSION AND TRANSPORT PROCESSES IN SPACE PLASMAS. AT EARTH'S MAGNETOPAUSE RECONNECTION PROCEEDS ASYMMETRICALLY BETWEEN THE MAGNETOSHEATH AND THE MAGNETOSPHERE PLASMAS. THE MAGNETOSHEATH PLASMA HAS A TYPICAL MAGNETIC FIELD STRENGTH ~ 20NT DENSITY ~ 5/CM^3 AND PLASMA- ~2; THE MAGNETOSPHERE PLASMA HAS MAGNETIC FIELD STRENGTH ~ 60 NT AND DENSITY ~ 0.5/CM^3 AND PLASMA- ~ 0.1. THE MAGNETIC FIELDS AT THESE TWO SIDES CAN SHEAR WITH AN ARBITRARY ANGLE. ONE FUNDAMENTAL QUESTION IS IS THERE A SIMPLE PRINCIPLE THAT DETERMINES THE ORIENTATION OF THE X-LINE IN SUCH A ASYMMETRIC CURRENT SHEET? THE SOLUTION OF THIS BASIC QUESTION REMAINS UNCLEAR WITH OUR CURRENT UNDERSTANDING OF MAGNETIC RECONNECTION PHYSICS AND WE AIM TO RESOLVE THIS ISSUE. ULTIMATELY WE HOPE TO DEVELOP A DECENT UNDERSTANDING ON THE THREE-DIMENSIONAL (3D) NATURE OF ASYMMETRIC MAGNETIC RECONNECTION ITSELF WHICH IS AN IMPORTANT STEP ON THE QUEST FOR PREDICTING THE LOCATION AND ORIENTATION OF MAGNETIC RECONNECTION AT EARTH S MAGNETOPAUSE. THE SAME PRINCIPLE THAT DETERMINES THIS LOCAL ORIENTATION COULD INTERPLAY WITH GLOBAL GEOMETRICAL EFFECTS IN THE REALISTIC MAGNETOPAUSE. IN ADDITION TO THOSE 2D SCENARIOS STUDIED BEFORE THE DEVELOPMENT OF X-LINE COULD SUBJECT TO RICH KINETIC FEATURES THAT ARE NOT YET TAKEN ACCOUNT IN THESE THEORETICAL MODELS. WE FORESEE THE IMPORTANCE OF THE FOLLOWING PHYSICAL PROCESSES. FIRST THE INCLUSION OF THE DIAMAGNETIC DRIFT RISING FROM THE STRONG PRESSURE GRADIENT CROSSING THE ASYMMETRIC CURRENT SHEET WILL BE PARTICULARLY INTERESTING. AS DEMONSTRATED IN 2D SIMULATIONS THE X-LINE COULD DRIFT OR EVEN BE SUPPRESSED BY DIAMAGNETIC DRIFTS. THIS WILL AFFECT THE CHOICE OF THE PREFERRED X-LINE ORIENTATION SINCE RECONNECTION AT DIFFERENT OBLIQUE PLANE DEVELOPS A DIFFERENT DRIFT SPEED AND EXPERIENCES A DIFFERENT DEGREE OF SUPPRESSION. SECOND AS THE SPREAD OF X-LINE COULD AFFECT THE DYNAMICAL EVOLUTION OF THE RECONNECTION PROCESS IT IS ALSO INTERESTING TO STUDY THE SPREAD OF THE X-LINE ALONG THE ORIENTATION IN SUCH AN ASYMMETRIC GEOMETRY AND ASK IF THE X-LINE HAS AN INTRINSIC FINITE EXTENT OR IF IT CAN EXTEND WITHOUT A LIMIT? THIRD OUR RECENT WORK DEMONSTRATES THE MASS RATIO DEPENDENCY OF X-LINE ORIENTATION WHICH IS CONSISTENT WITH THE ORIENTATION SHIFT OF THE MOST UNSTABLE TEARING MODE. HOWEVER MORE WORK IS REQUIRED TO GAIN A FUNDAMENTAL UNDERSTANDING IN ORDER TO FORMULATE A PREDICTION. THE PRIMARY APPROACH IN THIS PROJECT INCLUDES BOTH 2D AND 3D PIC SIMULATIONS. FOR 3D SIMULATIONS OUR APPROACH IS TO INDUCE A SINGLE X-LINE USING A LOCALIZED PERTURBATION SO THAT THE X-LINE HAS SUFFICIENT FREEDOM TO CHOOSE ITS ORIENTATION. THIS SETUP IS IDEAL IN SINGLING OUT THE DYNAMICS OF A SINGLE X-LINE AND AS DEMONSTRATED IN OUR PREVIOUS WORK A XLINE DEVELOPS WITH A WELL-DEFINED ORIENTATION. WE WILL ALSO TEST OUR PREDICTIONS USING THE ORIENTATION OF FTES IN THE DATASET OF THEMIS AND THE POTENTIAL SIGNAL OF X-LINE SPREADING OBSERVED BY SUPERDARN GROUND RADARS. THE PROPOSED RESEARCH IS RELEVANT TO THE GOAL #2 OF THE HIGH-LEVEL SCIENCE GOALS FROM THE HELIOPHYSICS DECADAL SURVEY- DETERMINE THE DYNAMICS AND COUPLING OF EARTH S MAGNETOSPHERE IONOSPHERE AND ATMOSPHERE AND THEIR RESPONSE TO SOLAR AND TERRESTRIAL INPUTS. THIS WORK IS ALSO TIMELY TO THE STUDY OF DAYSIDE RECONNECTION DURING THE FIRST PHASE OF NASA S MAGNETOSPHERIC MULTISCALE MISSION (MMS).