SA23B-01 13:40h
UV Remote Sensing of the Mesosphere With OSIRIS
The OSIRIS instrument on the Odin satellite includes an optical spectrograph that makes limb measurements of both scattered sunlight and the airglow in the wavelength range 280-800 nm. While the scattered sunlight in the mesosphere is quite bright (typically 1E4 R/A at 70 km) it is possible to identify airglow features that are excited through the resonant absorption of sunlight. In this paper we present new mesospheric observations in the wavelength region 300-325 nm and suggest that the airglow feature at 308 nm is due to emission from the OH (A-X) system. With this identification we can determine the mesospheric profile of OH in the ground vibrational state. The possibility of determining the water vapour profile in the mesosphere is also discussed.
SA23B-02 INVITED 13:55h
Observations of Lower Thermospheric Nitric Oxide from the Student Nitric Oxide Explorer
The production of nitric oxide is a key response of the upper atmosphere to solar energy deposition. NO plays a strong role in the thermospheric energy balance as it emits efficiently in the infrared, it is the terminal ion in the lower ionosphere, and if transported to lower altitudes will catalytically destroy ozone. NO is primarily produced through the reaction of excited atomic nitrogen with molecular oxygen. One of the primary loss mechanisms of NO is photodissociation by solar ultraviolet irradiance. In order to produce the excited atomic nitrogen atom, the strong N2 molecular bond must be broken. At low latitudes, solar soft X-ray irradiance is the energy source that leads to NO. At high latitudes, auroral electrons and the energetic secondary electrons provide the source of energy that leads to the large amounts of NO observed there. Coupling between latitude regions may occur as high latitude NO is transported by winds to lower latitude. In this talk we describe observations of NO from the Student Nitric Oxide Explorer (SNOE). SNOE observed fluorescently scattered sunlight by NO at 215 and 237 nm to obtain global concentrations of NO in the lower thermosphere daily from February 1998 through December 2003. We will present case studies of the observed response to large auroral storms. In particular, the effects of the large storms of April 2002 and November 2003 will be presented. The SNOE observations show that auroral energy deposition produces a significant global effect on the upper atmosphere.
SA23B-03 14:10h
The Cloud Imaging and Particle Size Experiment on AIM
The Cloud Imaging and Particle Size (CIPS) experiment on the NASA mission Aeronomy of Ice in the Mesosphere (AIM) will provide unprecedented coverage of Polar Mesospheric Cloud (PMC) morphology and microphysics. The AIM mission is scheduled for launch in the fall of 2006. CIPS is one of three science instruments on AIM, whose primary objective is to reveal why PMCs form and how & why they vary. CIPS will image the PMC cloud deck with 2 km resolution, and will measure the scattering phase function of PMCs along with other microphysical properties such as particle size and water content. The instrument consists of four wide angle cameras with a combined field of regard of 80 by 120 degrees. The camera field of view is centered at the nadir. The clouds are imaged at 265 nm, taking advantage of the strong absorption characteristic of ozone at this wavelength to enhance the contrast of the cloud scattering with respect to the background Rayleigh scattering. We will discuss the instrument characteristics and the technique to derive cloud properties.
SA23B-04 INVITED 14:25h
SHIMMER on STPSat-1: UV Spatial Heterodyne Spectroscopy for Space Based Remote Sensing of the Middle Atmosphere
SHIMMER, the Spatial Heterodyne Imager for Mesospheric Radicals is the primary payload of STPSat-1, a small satellite scheduled to be launched in late 2006 with a minimal lifetime of one year. SHIMMER will use Spatial Heterodyne Spectroscopy (SHS) to measure the limb brightness at 32 tangent altitudes with high spectral resolution (0.012nm) in a narrow bandpass around 308 nm. The solar resonance fluorescence of hydroxyl (OH) will be reduced from the limb profiles and inverted to provide OH concentration profiles for low to mid latitudes (up to 57 degrees). Since OH is a good proxy for water vapor in the upper mesosphere and lower thermosphere, water vapor concentrations will also be available from the data. We will review the basics of SHS, its differences and similarities to other spectroscopic techniques, and its suitability for the measurement of middle atmospheric OH in the UV. The specific design of SHIMMER on STPSat-1, which includes a monolithic SHS interferometer, will be presented. We will give a brief overview of the primary science goals of the SHIMMER on STPSat-1 mission and discuss the projected scientific return in context of its latitudinal coverage, atmospheric lighting conditions, and planned operations. In conclusion we will discuss the ability to make Polar Mesospheric Cloud observations with this instrument and how it can complement the NASA AIM (Aeronomy of Ice in the Mesosphere) mission, also scheduled for launch in late 2006. SHIMMER is a joint effort between the Naval Research Laboratory and the DoD Space Test Program (SMC/TEL)
SA23B-05 14:40h
Remote Sensing of molecular oxygen densities and temperatures in the thermosphere using Stellar Occultation Techniques
In this paper we present the results of stellar occultation observations in the thermosphere by the MSX/UVISI instrument. The extinction of stellar spectral signals in the O$_2$ Schumann-Runge continuum ($<$175 nm) provides a remote sensing tool to measure the O$_2$ number density profile in the thermosphere. The density profile then can be used to infer the thermospheric temperature under diffusive equilibrium assumption. Since the thermosphere has a large temperature gradient, increasing from 200K in the lower thermosphere up to $>$1000K in the upper thermosphere, accurate knowledge of the Schumann-Runge continuum cross sections as a function of temeperature is required. MSX/UVISI conducted over 50 UV stellar occultation experiments, covering a range of solar activities. In this paper, we use two sets of theoretically calculated cross-sections to retrieve the thermospheric O$_2$ density and temperature profiles. Comparisons with MSIS and NRLMSIS model prediction are made and differences between observations and model predictions are assessed. The accuracy of the temperature dependence of the O$_2$ absorption cross secctions will be evaluated based on the goodness of the fits to the observed occultation transmission spectra.
SA23B-06 INVITED 14:55h
The Special Sensor Ultraviolet Limb Imager (SSULI): An Ultraviolet Sensor of the Thermospheric and Ionospheric States
We present a brief overview of the Special Sensor Ultraviolet Limb Imager (SSULI) ultraviolet remote sensor that is currently in operation aboard the Defense Meteorlogical Satellite Program's F-16 satellite. The satellite is an a sun-synchronous orbit at 0730 local time, at a 98$\deg$ inclination, and a circular orbit at an altitude of $\sim$840 km. The instrument has been operating since mid-October 2003. We present an overview of the instrument's capabilities, its measurement goals, and some of the data that are being used for basic research.
SA23B-07 INVITED 15:10h
Far Ultraviolet Remote Sensing: Challenges and Opportunities
The far ultraviolet is commonly taken to be that spectral range from 115 nm to 185 nm. This definition reflects the practical nature and origin of the measurement technique. The short wavelength cut-off is defined by the transmittance cut-off of window materials (about 115 nm). The long wavelength end of the region is defined by the desire to exclude the orders-of-magnitude brighter signal at around 195 nm, which, happily, coincides with the fall-off in CsI photocathode efficiency at around 185 nm. The FUV allows us to probe the atmosphere down to about 130 km (as low as 80 km in H Lyman alpha). In this paper I will discuss what we have learned by using a novel imager, GUVI, on TIMED to study the ionosphere-thermosphere (IT) system, how we see the IT coupled to geospace and the solar input, and what we can learn from a future FUV system. In particular, I want to stress that FUV remote sensing is an important COMPONENT of a complete system for exploring the connections between the Sun, geospace, and the IT system. To that end, I will briefly discuss how those data need to be integrated into a virtual observatory that will enable new investigations into the near-Earth environment.
SA23B-08 15:25h
Characterization of Ionospheric Plasma Bubbles With the Global Ultraviolet Imager
Density depletions caused by plasma turbulence in the nighttime equatorial ionosphere referred to as ``Equatorial Spread-F'' (ESF) remain distressingly elusive despite several decades of observation, modeling, and theory. Recent FUV measurements of atomic oxygen recombination at 135.6 nm from the Global Ultraviolet Imager (GUVI) onboard the TIMED satellite provide an unprecedented opportunity to detect and investigate occurrence characteristics of ESF on a global scale. In this work, we present a comprehensive analysis of GUVI data using an automated bubble detection technique, in conjunction with tomographic image reconstruction methods capturing height-dependent plasma structures. Subsequent statistical analyses are performed to investigate and characterize the role of geomagnetic, solar, and seasonal influences on the triggering and development of equatorial plasma bubbles. Furthermore, we report on the analyses over several years to provide statistical information about the seasonal and longitudinal variations of ESF occurrence. Such long-term global analyses based on UV measurements contribute to the broader goal of understanding bubble formation patterns and consequently to a more accurate characterization of the mechanisms responsible for the generation and evolution of these plasma irregularities.