THIS INVESTIGATION AIMS TO QUANTITATIVELY EVALUATE IMPULSE PROPAGATION TIME IN THE MAGNETOSPHERE BY ANSWERING THE FOLLOWING SCIENCE QUESTIONS THAT ARE MOST CRITICAL AT THIS STAGE. THE SCIENCE QUESTIONS CAN BE DIVIDED INTO TWO GROUPS ADDRESSING THE PROPAGATION OF SI IN THE DAYSIDE MAGNETOSPHERE AND THAT OF NIGHTSIDE TRANSIENTS RESPECTIVELY. SCIENCE QUESTION 1 (SUDDEN IMPULSES): A. IS THE PROPAGATION TIME OF SUDDEN IMPULSES IN THE MAGNETOSPHERE BASED ON MULTI-SATELLITE OBSERVATIONS CONSISTENT WITH THE TAMAO TRAVEL-TIME MODEL? B. HOW DOES THE COMPARISON VARY WITH THE PROPERTIES OF THE SOLAR WIND DISCONTINUITY SUCH AS THE INCREASE IN THE DYNAMIC PRESSURE AND ORIENTATION OF THE DISCONTINUITY? C. HOW IS THE OBSERVED PROPAGATION TIME INCLUDING THE DEPENDENCE ON THE SOLAR WIND DISCONTINUITY COMPARED WITH THE GLOBAL SIMULATION RESULT? WHAT ARE THE IMPLICATIONS FOR THE FORWARD MODEL OF SI TRAVEL TIME? SCIENCE QUESTION 2 (NIGHTSIDE TRANSIENTS): A. WHAT IS THE PROPAGATION TIME PATTERN OF EARTH-BOUND TRANSIENTS BASED ON MULTI-SATELLITE OBSERVATIONS? DOES THE PROPAGATION TIME PATTERN DEPEND ON THE TRANSIENT TYPE SUCH AS BBFS AND SUBSTORM INITIATIONS IN THE MAGNETOTAIL? B. HOW DOES THE OBSERVED PROPAGATION TIME OF NIGHTSIDE TRANSIENTS COMPARE WITH THE TRAVEL TIME ALONG THE FAST-MODE PATH THE HIGHLATITUDE TAMAO PATH OR THE LOW-LATITUDE TAMAO PATH? C. WHAT ARE THE IMPULSE TRAVEL PATHS IDENTIFIED BY GLOBAL SIMULATIONS? WHAT ARE THE IMPLICATIONS OF THE MODEL RESULTS FOR THE COMPARISON FOUND IN SCIENCE QUESTION 2B? WHAT ARE THE IMPLICATIONS FOR THE FORWARD MODEL OF NIGHTSIDE-TRANSIENT TRAVEL TIME? THIS INVESTIGATION ADDRESSES THE PROPAGATION OF IMPULSES WITH SCALE LENGTHS COMPARABLE TO OR GREATER THAN THE SCALE LENGTHS OF THE VELOCITY GRADIENTS WHICH IS A FUNDAMENTAL PHYSICS PROBLEM AND YET FULLY UNDERSTOOD. AN ACCURATE DETERMINATION OF IMPULSE PROPAGATION TIME IS CRITICAL IN IDENTIFYING THE GENERATION AND COUPLING OF PROCESSES IN THE MAGNETOSPHERE. THIS INVESTIGATION CAN PROVIDE IMPORTANT VALIDATION OF THE TRAVEL-TIME FORWARD MODEL FOR FUTURE IMPLEMENTATION OF TRAVEL-TIME MAGNETOSEISMOLOGY. CARRYING OUT THIS INVESTIGATION NOW IS TIMELY BECAUSE CAN EXPAND THE RESEARCH SCOPE FOR CURRENTLY OPERATING AND FUTURE HELIOPHYSICS MISSIONS. THIS INVESTIGATION USES FIELDS AND PLASMA DATA FROM THEMIS VAN ALLEN PROBES GEOTAIL AND MMS MISSIONS TOGETHER WITH THE SOLAR WIND FROM ACE AND WIND. ALSO USED ARE SUPPORTING OBSERVATIONS FROM POLAR FAST GOES CLUSTER SWARM IMP-8 AND GROUNDBASED MAGNETOMETERS. TO AID THE DATA ANALYSIS AND INTERPRETATIONS WE EVALUATE IMPULSE PROPAGATION TIME BASED ON EMPIRICAL FIELD AND PLASMA MODELS AS WELL AS ON GLOBAL MHD OPENGGCM SIMULATIONS. THE PROPAGATION OF SUBSTORM ONSET SIGNAL IN THE MAGNETOTAIL AS A PART OF THIS INVESTIGATION ECHOES ONE OF THE OBJECTIVES OF THE THEMIS MISSION THAT IDENTIFIES THE TIME HISTORY OF SUBSTORM PHENOMENA. THE FOCUS OF THIS INVESTIGATION HOWEVER IS ON IMPULSE PROPAGATION TIME RATHER THAN ON THE GENERATION MECHANISMS OF SUBSTORMS. THIS INVESTIGATION ALSO EXAMINES THE PROPAGATION OF SI IN THE DAYSIDE MAGNETOSPHERE. THIS INVESTIGATION ALSO ADDRESSES GOAL #2 FROM THE MOST RECENT HELIOPHYSICS DECADAL SURVEY NAMELY "DETERMINE THE DYNAMICS AND COUPLING OF EARTH'S MAGNETOSPHERE IONOSPHERE AND ATMOSPHERE AND THEIR RESPONSE TO SOLAR AND TERRESTRIAL INPUTS." SPECIFICALLY UNDERSTANDING THE IMPULSE PROPAGATION TIME IS AN IMPORTANT ELEMENT IN IDENTIFYING THE GENERATION AND COUPLING OF PROCESSES IN THE SOLAR WIND-MAGNETOSPHERE-IONOSPHERE SYSTEM.