Chemistry of the Mesosphere III Posters
Presiding: A K Smith, NCAR Atmospheric Chemistry Division; D Marsh, NCAR Atmospheric Chemistry Division
SA43A-01 1330h
On the Two-Day Oscillations in Global 3D-Modeling of the Chemical System of the Upper Mesosphere/Mesopause Region
The integration of the photochemical system of the upper mesosphere/mesopause region brought evidence that the system is able to respond in a nonlinear manner under certain conditions. Under the action of the diurnally-periodic insolation, the system creates subharmonic oscillations or chaos if disregarding strong diffusion, and under special conditions it possesses multiple solutions. The models used in the past were simplified and idealized in view of the number of dimensions and the consideration of the full dynamics. On the basis of our global 3D-model of the dynamics and chemistry of the middle atmosphere (COMMA-IAP) we also found a nonlinear response in the photochemistry under realistic conditions. From our calculations we got period-2 oscillations of the photochemical system within confined latitudinal regions around the solstices but not during the equinoxes. We discuss these findings particularly in terms of the influence of realistic dynamics on the creation of nonlinear effects.
SA43A-02 1330h
The O(1S - 1D,3P) Line Intensity Ratio
The line intensity ratio of the two optically-forbidden atmospheric emissions, O(1S-1D) at 557.7 nm and O(1S-3P) at 297.2 nm, must be a single-valued number in the upper atmosphere because the upper level is common to both lines. The calculated transition probability ratio A(557.7)/A(297.2) is 16, by several authors, and the ratio found in the laboratory is significantly larger. Field observations require space-based instruments, in which case calibration between the two wavelengths is the critical issue. We circumvent this problem by using the O2 Herzberg I emission system as a bridge between the UV region below 310 nm and the ground-accessible region above that wavelength. These two spectral regions can be separately calibrated in terms of intensity, and the results of a disparate set of observations (satellite, rocket, ground-based) lead to A(557.7)/A(297.2) ratios that are consistently much smaller than the calculated value. These results have consequences for auroral and dayglow processes, and it is particularly important to ascertain the cause of the substantial difference between theory and observation.
SA43A-03 1330h
Rotational and Spin-Orbit Distributions of NO Observed by MIPAS/ENVISAT Under Auroral and Quiescent Conditions
5.3 Μm emission from nitric oxide was observed by the MIPAS instrument on board the ENVISAT satellite under auroral and quiescent conditions in 2003. The very high spectral resolution of the instrument (0.035 cm-1 unapodized) permits detailed study of the rotational and spin-orbit distributions of NO in the upper atmosphere. Spectral modeling of the NO(Δv = 1) fundamental band emissions was performed and compared with the results of a non-LTE atmospheric model. In the MIPAS data taken during the October/November solar storm, strong NO signal levels and increased rotational temperatures indicated high levels of auroral activity. The two primary sources of NO(v = 1) in the thermosphere are the collisional excitation of NO(v = 0) by O atoms and the chemical reactions of N(4S) and N(2D) atoms with O2. Auroral activity leads to increased production of N(4S) and N(2D) atoms, resulting in enhanced chemical formation of NO. The NO(v = 1) spin-orbit distributions were found to be subthermal for all measurements. Variations in the NO spin-orbit ratios indicate that NO(v = 1) produced by N + O2 has a hotter spin-orbit distribution than NO(v = 1) produced by O atom collisional pumping. Spin-orbit relaxation is slower than rotational relaxation, and therefore the NO spin-orbit ratio may be useful as a signature of the NO formation mechanism.
SA43A-04 1330h
A new mechanism for the production of highly vibrationally excited OH in the mesosphere: An ab initio study of the reactions of O2 (A 3 Σ+u and A' 3 Δu) + H
In an attempt to explain the observed nightglow emission from OH (v=10) in the mesosphere that has energy greater than the expthermicity of the H + O3 reaction, potential energy surfaces were calculated for the reactions fo high lying electronic states of O2(A3Σ+u and A' 3Δu) with atomic hydrogen H(2S) to produce the ground state products OH(2Π) + O(3P). From collinear two-dimensional scans, several adiabatic and nonadiabatic pathways have been identified. Multi-configurational single and double excitation configuration interaction calculations show that the adiabatic pathways on a 4Δ potential surface from O2(A' 3Δ) + H and a 4Σ+ potential surface from O2 (A 3Σ+u) + H are the most favorable, with the zero-point corrected barrier heights of as low as 0.191 eV and 0.182 eV, respectively, and the reactions are fast. The transition states for these pathways are collinear and early, and the reaction coordinate suggests that the potential energy release of ca. 3.8 eV (larger than the energy to excite OH to v=10) is likely to favor high vibrational excitation.
SA43A-05 1330h
Global and Seasonal Visualization of Mesospheric OH Emissions from SABER
On December 7, 2001, SABER, a cooled multichannel radiometer, was launched aboard the NASA TIMED satellite into a 625 km orbit and is functioning as planned. In January of 2002 the SABER instrument began returning airglow limb scan measurements from around the globe. Data now available include 65% of the year 2002, 75% of the year 2003, and nearly 100% of the year 2004. Experimental data were taken from SABER for two of SABER's ten radiometric channels centered at λ = 1.6 Μm and λ = 2.06 Μm as a measure of different levels of OH excitation. The objective of the research analysis reported in this paper is the optimal display of the three-dimensional dynamics of the global OH infrared airglow. Volume emission rate (VER) as a function of latitude, longitude, altitude, and time was computed. An investigation into seasonal effects on the global distribution of the OH airglow was performed for expanded 2004 data. Interpolation methods for optimizing geographic visualization were analyzed and compared. The Kriging method was found to have superior visualization and minimal mean squared error. The maximum VER often was found to be greater near the equator compared with values at high latitudes. Furthermore, the peak VER observed at the equator occurred at lower altitudes. In addition, seasonal differences between the two emission bands were explored and will be presented.
SA43A-06 1330h
Simulations of OH Nightglow at Sprite Temperature in the MLT Region
Recent observations reveal that temperature in the intense lightning discharge channels during sprite events in the mesosphere could be as high as 20,000 K. As is well known, most of chemical reaction rates are highly dependent on temperature. High temperature may enhance some chemical reactions while at the same time suppress other reactions. This work is aimed to investigate how sensitive are the OH chemical reactions to a temperature as high as the sprite temperature at 20,000 K. Preliminary results, ignoring dynamical effects, seem to indicate that number density of atomic O near 70km is reduced by 13 percents and that of O3 is reduced by 15 percents while the production of OH is greatly enhanced. Further work is underway to refine the model to better match the sprite condition.
SA43A-07 1330h
The Physical Properties of PMSE Ice Particles as Determined During DROPPS by Measurements With the Particle Impact Detector
The two Black Brant payloads flown during the DROPPS (Distribution and Role of Particles in the Polar Summer Mesosphere) rocket program were launched during early July, 1999 from Andoya Rocket Range (ARR), Norway. Both payloads included a Particle Impact Detector (PID) charge telescope onboard. Computer simulations have shown that the PID instrument had the potential to detect atmospheric ice particles within the mesosphere, having dimensions of a few nanometers. Ice particles of nanometer size are believed to be responsible for polar mesospheric summer echoes (PMSEs), such as those observed at an altitude of ~82-87 km over Andoya during the first DROPPS launch sequence. This talk will discuss the analysis of the PID data obtained from the DROPPS campaign and comparison of these data to the results obtained from the nanometer scale ice particle computer simulations. Intercomparison of the PID observations with the computer simulations provides information concerning the properties of the PMSE particles, including their "rocky" core size, ice mantle thickness and distribution.
SA43A-08 1330h
Processes That Account for the Ozone Maximum at the Mesopause
The presence of a maximum in ozone density and mixing ratio in the mesopause region has been known for several decades although the measurement data base is still limited. We have simulated the ozone maximum in a 3-dimensional dynamical chemical model. The largest component of the diurnal cycle in ozone is the difference between low concentrations in sunlight and high concentrations in darkness. However, the diurnal variability also has strong contributions from atmospheric tides and from slow changes in the background chemical concentrations following sunrise and sunset. In this study, we find that the magnitude of the ozone secondary maximum is closely tied to the temperature. The very cold temperatures at the mesopause accelerate the formation of ozone and inhibit the loss. This factor and the location of the atomic oxygen density maximum both contribute in approximately equal measure to determining the altitude of the ozone layer and both have a major impact on the ozone variability. The magnitude of the nighttime ozone maximum is sensitive to the eddy and molecular diffusion rates through the influence of these processes on the concentration of hydrogen, which destroys ozone.
SA43A-09 1330h
TIMED/SABER observations of mesospheric odd-oxygen and chemical heating
Odd-oxygen (Ox = O + O3) plays an important role in determining the energy budget of the mesosphere. The rates of important exothermic reactions depend either directly or indirectly on Ox concentrations, as does the rate at which energy is lost through airglow emissions. TIMED/SABER airglow measurements can thus be used to infer atomic oxygen and ozone densities and, through the use of photochemical models, chemical heating rates. This study combines SABER atomic oxygen and ozone observations to study mesospheric variability of Ox. Observations reveal significant seasonal and diurnal variability in odd-oxygen which affects chemical heating rates and the mesospheric energy budget.
SA43A-10 1330h
Lidar observations of polar mesospheric metal layers
Lidar observations at two high-latitude locations (Sondrestrom, Greenland and South Pole) have been used to study the Na and Fe layer in the MLT region. We will compare the hemispheric difference of Na layer in the polar region, summarize the seasonal variations of both Na and Fe layers, and study the summertime metal layer behaviors associated with the formation of PMCs.
http://isr.sri.com
SA43A-11 1330h
Gravity Wave Global Distributions from Three Satellite Infrared Limb Scanners During August
We compare global distributions of gravity waves (GWs) measured by three different instruments, UARS/CLAES, CRISTA and TIMED/SABER, in the month of August in different years (1992, 1997, 2002-2004, respectively) spanning a decade. We will discuss common features, such as convectively generated GWs above the Gulf of Mexico and the Kuro-Shio stream as well as strong GW activity on the edge of the southern hemisphere (SH) polar vortex. CRISTA and SABER data reach far into the mesosphere. This enables us to study the development of the global GW distributions with altitude. The convective regions can be clearly identified up to the lower mesosphere. The southern polar vortex maximum reaches up to 70km and stalls above. Instead, we observe above 70km a maximum located in the SH subtropics. We will discuss these observations considering effects of wave visibility, wave breaking, and slant wave propagation.
SA43A-12 1330h
Initial Wind Measurements of the Upper Mesosphere via Na Lidar at Arecibo
We conducted a study at the Arecibo Observatory to determine the feasibility to measure the neutral winds of the upper mesosphere via sodium lidar observations. A simple dye-laser transmitter was coupled to a commercial Fabry-Perot interferometer that we used in the receiver path to resolve the spectral features of Na. Transmitted linewidths were similar to the Doppler width of sodium, while the FPI spectral width was nearly ten times smaller, enabling adequate resolution across the Na line profile. The FPI was scanned across a free spectral range while multiple altitude profiles of the Na backscatter were sampled. For this paper we will discuss the technique used, supplemented by examples of vertical and off-vertical Na spectra, and will present our preliminary estimates of the neutral winds.
SA43A-13 1330h
Non-LTE Analysis of SABER 15 Îœm Limb Observations of the Summer 2002 Polar Mesopause Region
The SABER instrument on TIMED measures the limb radiance in ten broadband infrared channels for an altitude range that includes the mesosphere and lower thermosphere. In this altitude range the effects of non-local thermal equilibrium (non-LTE) must be included to understand the measurements. The non-LTE algorithms and computer code package developed to analyze CRISTA infrared spectral limb radiances were adapted for this purpose. We retrieved temperature profiles from the 15 Îœm limb radiances measured in the summer 2002 polar mesopause. The retrieved temperature profiles will be compared with other retrievals, the coincident falling sphere experiments of the MaCWAVE campaign, and climatological data. Sources of the discrepancies between the various results are discussed.