CEDAR Frontiers: Daytime Optical Aeronomy Duggirala Pallamraju and Supriya Chakrabarti Center for Space Physics, Boston University dpraju@bu.edu & supc@bu.edu Investigation of daytime upper atmospheric processes through optical methods Daytime Upper Atmosphere: o Large conductivities (compared with night time) increased ion-drag, reduced wind flows, shorted electric fields, increased neutral temperatures, etc. Reduction in neutral wind flow: Affects convection pattern and neutral dynamics in high-latitudes. Development of Appleton anomaly in low-latitudes modifies the neutral wind flow possibly controlling the day-to-day variability of generation of plasma irregularities in the night. The propagation of TIDs (Travelling Ionospheric Disturbances) are impeded. Regions of enhanced neutral gas temperatures become secondary sources for winds, impede propagation of winds, alter the photochemical reaction rates thereby affect the kinematics.

CEDAR Frontiers- Daytime Optical Aeronomy On average at any place on the surface of the Earth, 63.33 % of time is either twilight or day. Traditional (night time) optical measurements are suited for ~ 19% of the time. Many of the daytime neutral and Mesosphere-Ionosphere- Thermosphere-Magnetosphere coupling studies remain to be investigated during the 63.33 % of time when traditional measurements are not suitable. Distribution of yearly average of light incident on any typical location on Earth Typical topics of investigation: MI coupling during daytime. Quantify particle energies incident into the auroral latitudes during sunlit hours. Ground-based investigation of conjugacy of aurora. SAR-arcs during the day. Propagation of gravity-waves daytime over low-latitudes that are potentially seeds to plasma irregularities. CEDAR Frontiers- Daytime Optical Aeronomy

Sample measurements A) Magnetospheric Cusps during daytime B) Daytime Aurora over Boston Daytime aurora over Boston during severe magnetic storms observed by HIRISE (Pallamraju and Chakrabarti, 2005; GRL) Anomalous enhancement observed in 630.0nm daytime emissions on Nov 6, 2001 due to redistribution of neutrals from high-latitudes (Pallamraju et al., 2004; Annales Geophys.) C) Neutral composition over low-latitudes Cusp precipitation (from 1330-1518 UT) in daytime 630.0nm emissions (Pallamraju et al., 2004; GRL) CEDAR Frontiers- Daytime Optical Aeronomy

CEDAR Frontiers- Daytime Optical Aeronomy Measurements required: Ground-based daytime measurements at multiple wavelengths to investigate vertical coupling from Mesosphere to Thermosphere. Two-dimensional spatial maps of daytime optical emissions. Chain of daytime optical instruments to provide large spatial coverage Satellite measurements of: optical emissions during daytime, daytime composition, neutral winds (all components), neutral temperatures. Goals: Comprehensive understanding of aurora during the day. Improved understanding of triggering mechanisms of ESF. Thermospheric response of storm induced effects over mid-latitudes. Round-the-clock observations of neutral dynamics and composition. CEDAR Frontiers- Daytime Optical Aeronomy