D.P. Murtagh

An assessment of proposed O(1S) and O2(b1Σg+) nightglow excitation parameters

Abstract A database consisting of a number of simultaneously measured O( 1 D- 1 S) green line and O 2 ( b 1 Σ g + ) − X 3 Σ g )(0,0) atmospheric band nightglow emission profiles is examined to assess the general validity of the airglow excitation parameters recently proposed by McDade et al . (1986, Planet. Space Sci ., 34 , 789). The measured profiles were obtained under quite diverse atmospheric conditions and should, therefore, allow a critical assessment of the proposed parameters. Model green line emission profiles, calculated from the measured O 2 atmospheric band emission profiles using the proposed parameters, are compared with the green line profiles actually measured on each occasion. The measured and modelled green line profiles are found to be in good agreement under most conditions. The cases for which discrepancies exist are discussed in terms of inadequacies in either the background atmosphere adopted for the analyses or in the parameters themselves.

Eton 5: Simultaneous rocket measurements of the OH meinel Δυ = 2 sequence and (8,3) band emission profiles in the nightglow

Abstract Simultaneous rocket measurements of the emission profiles of the OH Meinel (8,3) band and the Δυ = 2 sequence at 1.61 μm are presented and analysed. It is shown that the υ = 8 level of the hydroxyl radical must suffer significant loss in the mesosphere due to collisions with O2 and/or N2. The rate coefficients for this removal process are obtained, for certain limiting assumptions about the excitation mechanism, and the coefficients are found to be in good agreement with those deduced from an independent analysis of ground-based observations. A variety of kinetic models, which reproduce the observed (8,3) band profile in some detail, predict Δυ = 2 sequence emission profiles which compare favourably with the measured profile in their total zenith intensities but not in their altitude distributions. The differences between the measured and modelled Δυ = 2 altitude profiles suggest that the 1.61 μm observations may have been contaminated by some unidentified vehicle-induced emission.

Mean state densities, temperatures and winds during the MAC/SINE and MAC/EPSILON campaigns

Abstract During 1987 two major field campaigns were conducted, mainly in northern Norway (in summer and late autumn), in which a total of 41 (26+15) in-situ temperature profiles were obtained by different techniques such as passive falling spheres, ionizalion gauges and mass spectrometers. Simultaneously, ground-based measurements of OH-temperatures and sodium lidar temperatures were performed for approximately 85 h and 104 h, respectively. In addition, a total of 67 (37 + 30) wind profiles were measured by in-situ techniques. Several radar systems measured winds almost continuously before, during and after the campaigns. The mean temperature profile for the summer campaign showed major deviations from a recently published reference atmosphere (CIRA 1986), whereas the differences between observations and model are smaller in autumn. In general, both the summer and autumn mean wind profiles agreed with CIRA 1986. Minor differences were attributed to tidal biases of the observations and ageostrophic components.

Scattering phase functions and particle sizes in noctilucent clouds

The MIDAS-DROPPS campaign conducted in Norway in 1999 provided a comprehensive study of the high-latitude summer mesopause region with rocket-borne and ground-based instrumentation. Optical photometers were flown on two rocket payloads through substantially different mesospheric conditions. On both flights, distinct noctilucent cloud (NLC) layers were detected. We present the first analysis of NLC scattering phase functions observed from sounding rockets. Applying Mie calculations, the angular dependence of the scattering is used to extract information about particle sizes. The first flight featured a weak NLC with small particles (r ≤ 20 nm) located below the core of a strong polar mesosphere radar echo (PMSE). The second flight took place in the absence of any detectable PMSE and probed a bright NLC optically dominated by particles in the size range 40–50 nm.

DROPPS: A study of the polar summer mesosphere with rocket, radar and lidar

DROPPS (The Distribution and Role of Particles in the Polar Summer Mesosphere) was a highly coordinated international study conducted in July, 1999 from the Norwegian rocket range (Andoya, Norway). Two sequences of rockets were launched. Each included one NASA DROPPS payload, containing instruments to measure the electrodynamic and optical properties of dust/aerosol layers, accompanied by European payloads (MIDAS, Mini-MIDAS, and/or Mini-DUSTY) to study the same structures in a complementary manner. Meteorological rockets provided winds and temperature. ALOMAR lidars and radars (located adjacent to the launch site) monitored the mesosphere for noctilucent clouds (NLCs) and polar mesosphere summer echoes (PMSEs), respectively. EISCAT radars provided PMSE and related information at a remote site (Tromso, Norway). Sequence 1 (5–6 July) was launched into a strong PMSE with a weak NLC present; sequence 2 (14 July) occurred during a strong NLC with no PMSE evident. Here we describe program details along with preliminary results.

The molecular oxygen band systems in the U.V. nightglow: Measured and modelled

Abstract High resolution, ground-based measurements of the near-ultraviolet portion of the terrestrial nightglow spectrum are analysed using a non-linear least-squares method to fit synthetic spectra of the Herzberg I, II, III and Chamberlain bands of O2. The presence of the Herzberg III system is not substantiated by the present measurements. The vibrational population distribution of the A3Σ+u state is obtained and, partly based on some assumptions, the vibrational population distributions of the other two emitting states (c1Σ−u and A′3Δu) are determined. The total intensities of the three systems are obtained under varying geophysical conditions for about 80 nights distributed over almost half a solar cycle. The measured co-variations of the Herzberg I and Herzberg II systems with simultaneously obtained green line intensities provide a set of quenching parameters for O2 (c1Σ−u). These parameters set an upper limit of 10% on the production efficiency of O2 (c1Σ−u) in the atomic oxygen association reaction and indicate that the ratio of quenching by O and O2 is much greater than 50 : 1. This is not in agreement with the values obtained by McDade et al. (1986, Planet. Space Sci.34, 789) for the precursor to either O(1S) or O2(b1Σ+g). Based on these results it is demonstrated that the Herzberg II emission should peak considerably below the Herzberg I and Chamberlain emissions. This may explain earlier difficulties in interpreting Herzberg data from the rocket experiments ETON and OASIS.

A comparison of PMSE and other ground-based observations during the NLC-91 campaign

Abstract During the period July–August 1991, observations were made of Polar Mesospheric Summer Echoes (PMSE) at 46.9 MHz and 224 MHz by the CUPRI and EISCAT radars, respectively, at two sites in northern Scandinavia. Those observations are compared here with observations of noctilucent clouds, energetic particle precipitation and magnetic disturbances. The appearance and morphology of PMSE are found to be closely correlated at the two frequencies and the two sites, 200 km apart. No correlation is found between PMSE and noctilucent clouds or magnetic disturbance. No correlation is found between energetic particle precipitation and the appearance of PMSE at 46.9 MHz for the whole time period. At 224 MHz, there is no evidence for a correlation before the beginning of August and only one event suggesting a possible correlation after the beginning of August. A minimum in occurrence frequency for PMSE is found between 16 and 21 UT (17–22 LST) which may be related to an expected minimum in background wind strength in that time interval.

ETON 6: A rocket measurement of the O2 Infrared Atmospheric (0-0) band in the nightglow

Abstract Co-ordinated rocket measurements of the O 2 ( a 1 Δ g −X 3 Σ g − ) Infrared Atmospheric (0-0) band emission profile and the atomic oxygen densities in an undisturbed night-time atmosphere are used to investigate the processes responsible for the excitation of O 2 ( a 1 Δ g ) in the terrestrial nightglow. It is shown that three-body recombination of atomic oxygen, and subsequent energy transfer processes, can explain only part of the observed emission profile and that at least two other sources of O 2 ( a 1 Δ g ) emission must exist. One of these additional sources, responsible for most of the emission observed below 90km, is identified as arising from the night-time residual of the very large dayglow 1 Δ g population. The other additional source is required to explain most of the emission observed above 95km. The processes responsible for this high altitude component cannot be identified but the vertical distribution of the required source function strongly resembles the profile of the atomic oxygen density squared and suggests that a two-body radiative recombination process may be involved. However, the measured zenith emission rates can also be explained without the high altitude source of O 2 ( a 1 Δ g ) if optical emission at 1.27 μm was induced by the rocket as it penetrated the nightglow layer.

High resolution spectroscopy of oxygen u.v. airglow

Abstract Ultraviolet spectra of the oxygen airglow and related visible emission features have been regularly measured for a period of 2 years from a site outside Stockholm, Sweden (59°N, 18°E). The instrumentation includes a 1 m Ebert-Fastie scanning spectrometer for high resolution (1.3 A) measurements and a six channel filter photometer. The high resolution measurements were confined to three spectral regions, each 130 A in extent. The filter photometers monitored the following airglow features: OI green line, O2 Atmospheric Band (0,1), O2 Herzberg I, airglow continuum at two wavelengths and 546 nm mercury line. High resolution spectra containing a mixture of O2 Herzberg I, Herzberg II and Chamberlain bands have been obtained under varying geophysical conditions. Analysis of these spectra is undertaken using a non-linear least-squares fitting technique allowing separation of individual bands. The O2 Herzberg I total system intensity, as derived from the (6,7) band, changes in an almost linear manner with the green line. The details of the co-variation support a direct excitation mechanism rather than an indirect process proposed to overcome the apparent disagreement between laboratory and rocket measurement. Intensity variations of factor of 10 on a scale of days and a factor of two within a single night have been measured, which imply changes in the atomic oxygen densities of at least a factor of three.

Measurements of odd oxygen in the polar region on 10 February 1984 during MAP/WINE

Abstract Abundances of atomic oxygen and ozone have been measured by various techniques over northern Scandinavia during the MAP/WINE campaign in the winter 1983–1984. On 10 February at Kiruna, Sweden, rocket experiments used resonance fluorescence and twin path absorption at 130 nm to measure [O]between 70 and 178 km. Rocket-borne measurements of nightglow at 557.7, 761.9 and 551.1 nm and at 1.27 μm have also been obtained and [O]values derived from the atmospheric band intensities. Ozone abundances between 50 and 90 km have been determined from rocket-borne measurements of the ν 3 9.6 μm nightglow intensity from Andoya, Norway, and Kiruna. These have been compared with [O 3 ] measured on the same day from the Solar Mesospheric Explorer satellite, using measurements of dayglow at 1.27 μm, and with results from other rocket launchings in MAP/WINE. The results show evidence of low, perhaps exceedingly low, [O] and below normal [O 3 ] above the mesopause. Below 75 km at night [O 3 ] exceeded earlier and subsequent observations in the campaign. The measurements were made during a minor stratospheric warming, characterised by an offset polar vortex centred near the measurement zone.