Considerable uncertainties remain in the global pattern of diurnal variation in stratospheric ozone, particularly lower to middle stratospheric ozone, which is the principal contributor to total column ozone. The Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) attached to the Japanese Experiment Module (JEM) on board the International Space Station (ISS) was developed to gather high-quality global measurements of stratospheric ozone at various local times, with the aid of superconducting mixers cooled to 4K by a compact mechanical cooler. Using the SMILES dataset, as well as data from nudged chemistry-climate models (MIROC3.2-CTM and SD-WACCM), we show that the SMILES observational data have revealed the global pattern of diurnal ozone variations throughout the stratosphere. We also found that these variations can be explained by both photochemistry and dynamics. The peak-to-peak difference in the stratospheric ozone mixing ratio (total column ozone) reached 8% (1%) over the course of a day. This variation needs to be considered when merging ozone data from different satellite measurements and even from measurements made using one specific instrument at different local times.
Research Containing: Earth Observation
Sunset–sunrise difference in solar occultation ozone measurements (SAGE II, HALOE, and ACE–FTS) and its relationship to tidal vertical winds
This paper contains a comprehensive investigation of the sunset–sunrise difference (SSD, i.e., the sunset-minus-sunrise value) of the ozone mixing ratio in the latitude range of 10° S–10° N. SSD values were determined from solar occultation measurements based on data obtained from the Stratospheric Aerosol and Gas Experiment (SAGE) II, the Halogen Occultation Experiment (HALOE), and the Atmospheric Chemistry Experiment–Fourier transform spectrometer (ACE–FTS). The SSD was negative at altitudes of 20–30 km (−0.1 ppmv at 25 km) and positive at 30–50 km (+0.2 ppmv at 40–45 km) for HALOE and ACE–FTS data. SAGE II data also showed a qualitatively similar result, although the SSD in the upper stratosphere was 2 times larger than those derived from the other data sets. On the basis of an analysis of data from the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) and a nudged chemical transport model (the specified dynamics version of the Whole Atmosphere Community Climate Model: SD–WACCM), we conclude that the SSD can be explained by diurnal variations in the ozone concentration, particularly those caused by vertical transport by the atmospheric tidal winds. All data sets showed significant seasonal variations in the SSD; the SSD in the upper stratosphere is greatest from December through February, while that in the lower stratosphere reaches a maximum twice: during the periods March–April and September–October. Based on an analysis of SD–WACCM results, we found that these seasonal variations follow those associated with the tidal vertical winds.
Six-channel spectrophotometers (PH) are the science instruments of JEM-GLIMS to measure absolute intensity of the emission originated from lightning discharges and upper atmospheric transient luminous events (TLEs). PH unit-1 (PH-U1) consists of four spectrophotometer channels named from PH1 to PH4, while PH unit-2 (PH-U2) two spectrophotometer channels named PH5 and PH6. Optical filters of these spectrophotometers are selected to detect TLE emission lines of N2 1PG, N2 2PG, N2+ 1NG, and N2 LBH. Since the bandwidth of the optical filter of PH2, 3, 5, and 6 is 10 nm and since PH1 measures NUV emission, photomultiplier tubes with high-voltage converters are used as a photon detector. To the contrary, PH4 uses a photodiode as a photon detector because the pass-band of the optical filter is enough wide to detect transient optical emission. Though PH does not equip spatial resolution, it can acquire light curve data with a high time resolution of 50 μs with a 12-bit resolution. Thus, the combinational analysis of PH data and Lightning and Sprite Imager (LSI) data, it is possible to clarify the relationship between TLEs and their parent lightning discharges, the occurrence condition of TLEs, and the energy of the electrons which excite TLE emission.
Measurement of the pressure broadening coefficient of the 625 GHz transition of H2O2H2O2 in the sub-millimeter-wave region
The hydrogen peroxide ( H 2 O 2 ) molecule plays an important role in stratospheric ozone chemistry as a reservoir molecule in the HO X cycle. The Superconducting Sub-Millimeter-Wave Limb Emission Sounder (SMILES) instrument in the Japanese Experiment Module (JEM) on the International Space Station monitors H 2 O 2 using the pure rotational J Ka , Kc = 20 1 , 19 – 19 2 , 17 transition at 625.044 GHz in the ground vibronic state. Accurate retrievals of H 2 O 2 abundances rely on a knowledge of pressure broadening effects for this transition, and the required nitrogen ( N 2 ) and oxygen ( O 2 ) broadening coefficients are measured here for the first time. Values of the pressure broadening coefficients, γ ( N 2 ) = 4.03 ± 0.06 MHz / Torr and γ ( O 2 ) = 2.49 ± 0.04 MHz / Torr are obtained at room temperature, with statistical 3 σ uncertainties given. The value for air broadening is then derived to be γ ( air ) = 3.71 ± 0.09 MHz / Torr , where the uncertainty includes possible systematic errors.
Ozone is known to have large oxygen isotopic enrichments of about 10% in the middle stratosphere; however, there have been no reports of ozone isotopic enrichments above the middle stratosphere. We derived an enrichment δ18OOO in the stratosphere and the lower mesosphere from observations of the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) onboard the International Space Station (ISS) using a retrieval algorithm optimized for the isotopic ratio. The retrieval algorithm includes (i) an a priori covariance matrix constrained by oxygen isotopic ratios in ozone, (ii) an optimization of spectral windows for ozone isotopomers and isotopologues, and (iii) common tangent height information for all windows. The δ18OOO by averaging the SMILES measurements at the latitude range of 20 to 40° N from February to March in 2010 with solar zenith angle < 80° was 13% (at 32 km) with the systematic error of about 5%. SMILES and past measurements were in good agreement, with δ18OOO increasing with altitude between 30 and 40 km. The vertical profile of δ18OOO obtained in this study showed an increase and a decrease with altitude in the stratosphere and mesosphere, respectively. The δ18OOO peak, 18%, is found at the stratopause. The δ18OOO has a positive correlation with temperature in the range of 220–255 K, indicating that temperature can be a dominant factor to control the vertical profile of δ18OOO in the stratosphere and mesosphere. This is the first report of the observation of δ18OOO over a wide altitude range extending from the stratosphere to the mesosphere (28–57 km).
ICESat elevation profiles of tabular iceberg margins and the Ronne Ice Shelf edge reveal shapes indicative of two types of bending forces. Icebergs and shelf fronts in sea-ice-covered areas have broad (∼1000 m wide), rounded, ∼0.6 m high ‘berms’ and outer edges that slope down several meters toward the water. Bergs in warmer water have 2 to 5m ‘ramparts’ with ∼1500 m wide edge-parallel ‘moats’ inboard of the edge. This latter pattern was first revealed in images from International Space Station (ISS) showing edge-parallel melt ponds on one iceberg just prior to its disintegration. Model results indicate the patterns are caused by hydrostatic and lithostatic forces acting on the ice face. ‘Berm’ profiles arise from differences between ice and water pressure along the face. ‘Rampart-moat’ profiles result from waterline erosion, creating a submerged bench of ice that lifts the ice edge. We use the results to discuss iceberg breakup at low latitudes.
Characterization of sensitivity degradation seen from the UV to NIR by RAIDS on the International Space Station
This paper presents an analysis of the sensitivity changes experienced by three of the eight sensors that comprise the Remote Atmospheric and Ionospheric Detection System (RAIDS) after more than a year operating on board the International Space Station (ISS). These sensors are the Extreme Ultraviolet Spectrograph (EUVS) that covers 550-1100 Å, the Middle Ultraviolet (MUV) spectrometer that covers 1900-3100Å, and the Near Infrared Spectrometer (NIRS) that covers 7220-8740 Å. The scientific goal for RAIDS is comprehensive remote sensing of the temperature, composition, and structure of the lower thermosphere and ionosphere from 85-200 km. RAIDS was installed on the ISS Japanese Expansion Module External Facility (JEM-EF) in September of 2009. After initial checkout the sensors began routine operations that are only interrupted for sensor safety by occasional ISS maneuvers as well as a few days per month when the orbit imparts a risk from exposure to the Sun. This history of measurements has been used to evaluate the rate of degradation of the RAIDS sensors exposed to an environment with significant sources of particulate and molecular contamination. The RAIDS EUVS, including both contamination and detector gain sag, has shown an overall signal loss rate of 0.2% per day since the start of the mission, with an upper boundary of 0.13% per day attributed solely to contamination effects. This upper boundary is driven by uncertainty in the change in the emission field due to changing solar conditions, and there is strong evidence that the true loss due to contamination is significantly smaller. The MUV and NIRS have shown stability to within 1% over the first year of operations.
We present the first published measurement of an altitude profile of the O II 61.7 nm emission, a dayglow feature that can be used to monitor photoionization of O in the lower thermosphere. This photoionization process also results in the O II 83.4 nm emission that, unlike 61.7 nm, is resonantly scattered by ionospheric O+. Although ionospheric characteristics can be inferred from the shape and intensity of 83.4 nm altitude profiles, the interpretation can result in nonunique ion density profiles if the intensity of this source of photons that illuminates the ionosphere from below is unknown. The 61.7 nm emission provides a means to test the accuracy of current models used to calculate the intensity of that source. The data presented here were collected by the Remote Atmospheric and Ionospheric Detection System from the International Space Station on 29 October 2009. The measured 61.7 nm profiles show a steeper drop in intensity below 260 km, where the emission peaks, compared to our model calculations. While the current analysis cannot resolve if the discrepancy is caused by inaccuracies in our model thermospheric composition, photoabsorption cross sections, or both, a 15%–20% increase in the effective O2 photoabsorption at 61.7 nm produces the best qualitative match to the measured profile. Ostensibly, 61.7 nm measurements could replace these model calculations as a more direct measure of the intensity of the 83.4 nm photon source region. In either case, accurate specification of local thermospheric neutral species remains an important component of daytime ionospheric remote sensing.
HCl and ClO profiles inside the Antarctic vortex as observed by SMILES in November 2009: comparisons with MLS and ACE-FTS instruments
We present vertical profiles of hydrogen chloride (HCl) and chlorine monoxide (ClO) as observed by the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on the International Space Station (ISS) inside the Antarctic vortex on 19–24 November 2009. The SMILES HCl value reveals 2.8–3.1 ppbv between 450 K and 500 K levels in potential temperature (PT). The high value of HCl is highlighted since it is suggested that HCl is a main component of the total inorganic chlorine (Cly), defined as Cly ≃ HCl + ClO + chlorine nitrate (ClONO2), inside the Antarctic vortex in spring, owing to low ozone values. To confirm the quality of two SMILES level 2 (L2) data products provided by the Japan Aerospace Exploration Agency (JAXA) and Japan's National Institute of Information and Communications Technology (NICT), vis-à-vis the partitioning of Cly, comparisons are made using other satellite data from the Aura Microwave Limb Sounder (MLS) and Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). HCl values from the SMILES NICT L2 product agree to within 10% (0.3 ppbv) with the MLS HCl data between 450 and 575 K levels in PT and with the ACE-FTS HCl data between 425 and 575 K. The SMILES JAXA L2 product is 10 to 20% (0.2–0.5 ppbv) lower than that from MLS between 400 and 700 K and from ACE-FTS between 500 and 700 K. For ClO in daytime, the difference between SMILES (JAXA and NICT) and MLS is less than ±0.05 ppbv (100 %) between 500 K and 650 K with the ClO values less than 0.2 ppbv. ClONO2 values as measured by ACE-FTS also reveal 0.2 ppbv at 475–500 K level, resulting in the HCl / Cly ratios of 0.91–0.95. The HCl / Cly ratios derived from each retrieval agree to within −5 to 8 % with regard to their averages. The high HCl values and HCl / Cly ratios observed by the three instruments in the lower stratospheric Antarctic vortex are consistent with previous observations in late Austral spring.
Littoral river plumes are complex optical environments. To begin to resolve this complexity we use hyperspectral data, and an extension of ‘dark pixel correction’ methods (Chavez 1988), to produce radiance maps that allow us to distinguish different constituents in the water column ranging from glacial rich sediments (silica’s) to muds and algae. We present data from two sites: the Columbia River in the Northwest of the United States, and the Otago Shelf fed by the Clutha River on the South Island of New Zealand. For this study the instrument used to collect data was HICO (Corson 2010; Davis et. al. 2010) — the Hyperspectral Imager for the Coastal Ocean — developed by the United States Naval Research Lab (NRL) and currently flying on the International Space Station. HICO has 90 channels between 400-900 nm and a ground sampling distance of 90 m. These early results illustrate how space borne hyperspectral imaging can enhance our view of the suspended matter in iver plumes along a coast.