SCIENCE GOALS AND OBJECTIVES: THE GOAL OF THIS STUDY IS TO INVESTIGATE IONOSPHERIC IRREGULARITIES AT LOW AND MIDLATITUDES AND TO IDENTIFY THE PROCESSES RESPONSIBLE FOR THEIR OCCURRENCE. OBJECTIVES INCLUDE THE ANALYSIS OF INTRUSION OF EQUATORIAL PROCESSES INTO MIDLATITUDES AND IDENTIFICATION OF IRREGULARITIES GENERATED LOCALLY AND HOW THEY DIFFER FROM THE ONES GENERATED AT LOWER LATITUDES. CASE STUDIES DURING GEOMAGNETIC ACTIVE DAYS WILL ALSO BE INVESTIGATED. IN ORDER TO ACHIEVE THIS GOAL AND OBJECTIVES DATA FROM ICON WILL BE ANALYZED. ICON S ORBIT IS IN A 27O INCLINATION AT ~600 KM AND ALLOWS US TO STUDY THE LOW AND MIDLATITUDE IONOSPHERE THROUGH THE USE OF ION VELOCITY METER (IVM) PLASMA DENSITIES AND VELOCITIES. DURING QUIET GEOMAGNETIC CONDITIONS IONOSPHERIC PERTURBATIONS ASSOCIATED WITH EQUATORIAL SPREAD F ARE USUALLY OBSERVED IN THE 0-15O MAGNETIC LATITUDE RANGE. POLEWARD FROM THIS RANGE THE COMMON NIGHTTIME STRUCTURE IS RELATED TO MEDIUM SCALE TRAVELLING IONOSPHERIC DISTURBANCES (MSTIDS) GENERATED LOCALLY. DURING HIGH MAGNETIC ACTIVITY STUDIES HAVE SHOWN THAT ESF STRUCTURES CAN REACH MIDLATITUDES. BUT OTHER STUDIES HAVE CLAIMED THAT THE DEPLETIONS ARE NOT RELATED TO ESF BUT ARE GENERATED LOCALLY (I.E. MSTIDS). THIS STUDY WILL INVESTIGATE THE CHARACTERISTICS OF PLASMA DATA AT DIFFERENT LATITUDES. IT WILL ALSO LOOK AT DATA DURING HIGH GEOMAGNETIC ACTIVITY. THE STUDY AIMS TO ADDRESS THE ADVERSE EFFECTS OF IONOSPHERIC IRREGULARITIES ON COMMUNICATIONS AND NAVIGATIONAL SYSTEMS IN A REGION THAT HISTORICALLY HAS BEEN CONSIDERED TO BE BENIGN . COMPLEMENTARY INFORMATION FOR NOTABLE CASES WILL BE OBTAINED FROM ALL-SKY IMAGERS AND TOTAL ELECTRON CONTENT (TEC) DATA FROM INDIVIDUAL GLOBAL NAVIGATION SATELLITE SYSTEM (GNSS) RECEIVERS. THESE GROUND-BASED DATA WILL BE USED TO HELP TO INTERPRET ICON DATA AND WILL NOT BE THE PRIMARY OBJECT OF THE INVESTIGATION. METHODOLOGY: THE IVM INSTRUMENT ON BOARD OF ICON WILL PROVIDE ION DENSITY AND VELOCITY DATA TO IDENTIFY NIGHTTIME IONOSPHERIC PERTURBATIONS AT LOW AND MIDLATITUDES. WE WILL INVESTIGATE THE IN-SITU DATA IN THE AMERICAN LONGITUDE SECTOR WITH EMPHASIS IN PROCESSES OCCURRING IN CONTINENTAL US CENTRAL AMERICA CARIBBEAN REGION AND SOUTH AMERICA. THE IVM DATA WILL BE ANALYZED BY IMPLEMENTING A SIGNAL DETRENDING PROCEDURE THAT CAN DEAL WITH SITUATIONS WHEN PLASMA DEPLETIONS AND WAVE-LIKE FLUCTUATIONS ARE PRESENT. ONCE DEPLETED ION DENSITY SIGNATURES ARE IDENTIFIED WE WILL PERFORM POWER SPECTRUM ANALYSIS USING SHORT TIME FOURIER TRANSFORM TO EXTRACT THE RELEVANT PARAMETERS RELATED TO THE IRREGULARITIES SCALE SIZES. FOR NOTABLE CASES THE TRAJECTORY OF ICON WILL BE MAPPED ALONG MAGNETIC FIELD LINE TO 250 KM IN BOTH HEMISPHERES. THIS MAPPING ASSUMES THAT LARGE SCALE PERTURBATIONS OBSERVED IN-SITU BY ICON BEAR RELATION TO THE IONOSPHERIC CONDITIONS AT 250 KM. CONJUNCTIONS WITH ALL-SKY IMAGERS AND GROUND-BASED GNSS RECEIVERS WILL BE IDENTIFIED. SELECTED GNSS-DERIVED TEC DATA WILL BE ANALYZED AND RATE OF CHANGE OF TEC AND POWER SPECTRUM WILL BE OBTAINED. THE 2D OBSERVATIONS FROM ALL-SKY IMAGERS CAN PROVIDE SPATIAL AND TEMPORAL CONTEXT TO SATELLITE AND GPS DATA. RELEVANCE TO HELIOPHYSICS GOAL OR SPECIFIC OBJECTIVES: THE PROPOSED WORK HAS DIRECT RELEVANCE TO ONE OF THE FOUR HIGH-LEVEL SCIENCE GOALS FROM THE MOST RECENT HELIOPHYSICS GOAL OR SPECIFIC OBJECTIVES. IT WILL ADDRESS THE DYNAMICS AND COUPLING OF EARTH S MAGNETOSPHERE IONOSPHERE AND ATMOSPHERE THROUGH THE STUDY OF IONOSPHERIC IRREGULARITIES AT LOW AND MIDLATITUDES REGIONS. THIS STUDY WILL DEVELOP THE KNOWLEDGE AND CAPABILITY TO DETECT CONDITIONS IN THE UPPER ATMOSPHERE THAT CAN ADVERSELY AFFECT RADIO COMMUNICATION AND NAVIGATIONAL SYSTEMS. IT WILL ALSO ADVANCE OUR UNDERSTANDING OF THE CONNECTIONS BETWEEN SOLAR VARIABILITY AND EARTH SPACE ENVIRONMENT.