As part of the second SPARC (Stratosphere–troposphere Processes And their Role in Climate) water vapor assessment (WAVAS-II), we present measurements taken from or coincident with seven sites from ...which ground-based microwave instruments measure water vapor in the middle atmosphere. Six of the ground-based instruments are part of the Network for the Detection of Atmospheric Composition Change (NDACC) and provide datasets that can be used for drift and trend assessment. We compare measurements from these ground-based instruments with satellite datasets that have provided retrievals of water vapor in the lower mesosphere over extended periods since 1996. We first compare biases between the satellite and ground-based instruments from the upper stratosphere to the upper mesosphere. We then show a number of time series comparisons at 0.46 hPa, a level that is sensitive to changes in H2O and CH4 entering the stratosphere but, because almost all CH4 has been oxidized, is relatively insensitive to dynamical variations. Interannual variations and drifts are investigated with respect to both the Aura Microwave Limb Sounder (MLS; from 2004 onwards) and each instrument's climatological mean. We find that the variation in the interannual difference in the mean H2O measured by any two instruments is typically ∼ 1%. Most of the datasets start in or after 2004 and show annual increases in H2O of 0–1 % yr−1. In particular, MLS shows a trend of between 0.5 % yr−1 and 0.7 % yr−1 at the comparison sites. However, the two longest measurement datasets used here, with measurements back to 1996, show much smaller trends of +0.1 % yr−1 (at Mauna Loa, Hawaii) and −0.1 % yr−1 (at Lauder, New Zealand).
Time series of stratospheric and lower mesospheric water vapour
using 33 data sets from 15 different satellite instruments were compared in
the framework of the second SPARC (Stratosphere-troposphere ...Processes And
their Role in Climate) water vapour assessment (WAVAS-II). This comparison
aimed to provide a comprehensive overview of the typical uncertainties in the
observational database that can be considered in the future in observational
and modelling studies, e.g addressing stratospheric water vapour trends. The
time series comparisons are presented for the three latitude bands, the
Antarctic (80∘–70∘ S), the tropics
(15∘ S–15∘ N) and the Northern Hemisphere mid-latitudes
(50∘–60∘ N) at four different altitudes (0.1, 3, 10 and
80 hPa) covering the stratosphere and lower mesosphere. The combined
temporal coverage of observations from the 15 satellite instruments allowed
the consideration of the time period 1986–2014. In addition to the
qualitative comparison of the time series, the agreement of the data sets is
assessed quantitatively in the form of the spread (i.e. the difference
between the maximum and minimum volume mixing ratios among the data sets),
the (Pearson) correlation coefficient and the drift (i.e. linear changes of
the difference between time series over time). Generally, good agreement
between the time series was found in the middle stratosphere while larger
differences were found in the lower mesosphere and near the tropopause.
Concerning the latitude bands, the largest differences were found in the
Antarctic while the best agreement was found for the tropics. From our
assessment we find that most data sets can be considered in future
observational and modelling studies, e.g. addressing stratospheric and lower
mesospheric water vapour variability and trends, if data set specific
characteristics (e.g. drift) and restrictions (e.g. temporal and spatial
coverage) are taken into account.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
We present analysis of a bright haze observed inside Valles Marineris, which formed in mid northern spring. The data were collected by the High Resolution Stereo Camera (HRSC) and the imaging ...spectrometer, Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité (OMEGA), aboard Mars Express. This study provides a case example of the power of simultaneous multiple emission angle and hyperspectral imaging for study of aerosols and clouds in the Martian atmosphere. The haze appeared thinner after three days and disappeared in nine days. It was limited to a 2‐km layer at the bottom of the canyon. The color was redder than the underlying surface. The analysis of the OMEGA spectra indicates that this haze was composed of dust particles. The dust layer appeared brighter with the HRSC stereo channels than the nadir channel due to longer scattering paths. We have estimated the optical depth of the haze by fitting both HRSC and OMEGA data with radiative transfer calculations. The retrieval of the optical depth is very sensitive to the aerosol scattering model used and the reflectance of the surface. Applying an aerosol scattering model derived from sky surveys at a constant elevation by the Imager for Mars Pathfinder, the optical depth of the haze is estimated from HRSC data to be within 1.7 to 2.3 at the wavelength (λ) of 0.675 μm. The wavelength dependence is obtained from OMEGA spectrum. It increases to 2.2–2.6 at λ = 1.35 μm and moderately decreases to 1.2–1.8 at λ = 2.4 μm.
In this paper we present evidence of enhanced N2O concentrations in the upper stratosphere/lower mesosphere polar regions after the solar proton events that occurred during October–November 2003. The ...observations were performed by the MIPAS instrument on the Envisat satellite. Simulations performed using the Canadian Middle Atmospheric Model (CMAM) show that such enhancements are most likely produced by the reaction of N(4S) with NO2, both of which species are largely enhanced just after the solar proton events in the winter polar night.
The presence of planetary wave type oscillations at mid-latitudes in the mesosphere/lower thermosphere region has been investigated using airglow observations. The observations were taken with a ...Spectral Airglow Temperature Imager (SATI) installed at Sierra Nevada Observatory (37.06° N, 3.38° W) at 2900 m height. Airglow data of the column emission rate of the O2 Atmospheric (0-1) band and of the OH Meinel (6-2) band and deduced rotational temperatures from 1998 to 2007 have been used in this study. From these observations a climatology of planetary wave type oscillations at this location is inferred. It has been found that the planetary wave type oscillations of 5-day period is predominant in our data throughout the year, with activity greater than 50% during March/April and October/November months. The planetary wave type oscillations of 2-day period is predominant during both solstices, being predominant during winter solstice in O2 while a 10-day oscillation appears throughout the year with activity around 20% and with maximum activity during spring and autumn equinoxes. The 16-day oscillation has maximum occurrence during autumn-winter while its activity is almost disappeared during spring-summer. No clear seasonal dependence of the amplitude of the planetary wave type oscillations was observed in the cases considered in this study. The waves simultaneously detected in the rotational temperatures deduced from both OH and O2 emissions usually show an upward energy propagation and are affected by dissipation processes.
The SABER instrument on board the TIMED satellite, successfully launched on 7 December 2001, measures the CO2 4.3 μm atmospheric emission at day and night, from the troposphere up to the ...thermosphere, with a near global latitude coverage and with a very high signal‐to‐noise ratio. SABER has also three channels near 15 μm for the measurements of the pressure‐temperature structure and two channels around 2.0 and 1.6 μm, mainly sensitive to the OH(υ ≤ 9) overtone radiation from levels υ = 8–9 and υ = 3–5, respectively. In this paper we analyze the measurements of SABER in channel 7, centered near 4.3 μm, taken at night in the upper mesosphere and lower thermosphere under quiet (nonauroral) conditions. The measurements of the 4.3 μm radiance in this region are much larger than expected under local thermodynamic equilibrium (LTE) and show a strong correlation with the OH channel signal. It was proposed by Kumer et al. 1978 that the CO2(υ3) levels, responsible for the emission at 4.3 μm, were excited from OH(υ) via vibrational‐vibrational energy transfer with N2(1) and hence to CO2(υ3). SABER data (measuring simultaneously pressure, temperature, CO2 4.3 μm emission, and OH(υ) near‐IR emission) offer an unprecedented data set for understanding the non‐LTE excitation mechanisms of CO2(υ3) in the nighttime mesosphere. We have investigated the SABER 4.3 μm radiances with the help of a non‐LTE radiative transfer model for CO2 and found that the large radiances can be explained by a fast and efficient energy transfer rate from OH(υ) to N2(1) to CO2(υ3), whereby, on average, 2.8–3 N2(1) vibrational quanta are excited after quenching of one OH(υ) molecule. A series of alternative excitation mechanisms that may enhance the nighttime 4.3 μm limb radiance were considered and found to be insignificant. The mechanism(s) whereby the energy is transferred from OH(υ) to N2(υ) is (are) still uncertain. The populations of OH(υ) are not significantly affected by incorporation of this fast transfer since N2 quenching of OH(υ) is negligible when compared to O2 quenching.
Hydrocarbon species, and in particular CH
4
, play a key role in the stratosphere-thermosphere boundary of Jupiter, which occurs around the μ-bar pressure level. Previous analyses of solar ...occultation, He and Ly-α airglow, and ISO/SWS measurements of the radiance around 3.3 μm have inferred significantly different methane concentrations. Here we aim to accurately model the CH
4
radiance at 3.3 μm measured by ISO/SWS by using a comprehensive non-local thermodynamic equilibrium model and the most recent collisional rates measured in the laboratory for CH
4
to shed new light onto the methane concentration in the upper atmosphere of Jupiter. These emission bands have been shown to present a peak contribution precisely at the μ-bar level, hence directly probing the region of interest. We find that a high CH
4
concentration is necessary to explain the data, in contrast with the most recent analyses, and that the observations favour the lower limit of the latest laboratory measurements of the CH
4
collisional relaxation rates. Our results provide precise constraints on the composition and dynamics of the lower atmosphere of Jupiter.
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FMFMET, NUK, UL, UM, UPUK
Airglow observations with a Spectral Airglow Temperature Imager (SATI), installed at the Sierra Nevada Observatory (37.06° N, 3.38° W) at 2900-m height, have been used to investigate the presence of ...tidal variations at mid-latitudes in the mesosphere/lower thermosphere region. Diurnal variations of the column emission rate and vertically averaged temperature of the O2 Atmospheric (0-1) band and of the OH Meinel (6-2) band from 5 years (1998-2003) of observations have been analysed. From these observations a clear tidal variation of both emission rates and rotational temperatures is inferred. It is found that the amplitude of the daily variation for both emission rates and temperatures is greater from late autumn to spring than during summer. The amplitude decreases by more than a factor of two during summer and early autumn with respect to the amplitude in the winter-spring months. Although the tidal modulations are preferentially semidiurnal in both rotational temperatures and emission rates during the whole year, during early spring the tidal modulations seem to be more consistent with a diurnal modulation in both rotational temperatures and emission rates. Moreover, the OH emission rate from late autumn to early winter has a pattern suggesting both diurnal and semidiurnal tidal modulations.
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