Overview of the EOS aura mission Schoeberl, M.R.; Douglass, A.R.; Hilsenrath, E. ...
IEEE transactions on geoscience and remote sensing,
05/2006, Volume:
44, Issue:
5
Journal Article
Peer reviewed
Open access
Aura, the last of the large Earth Observing System observatories, was launched on July 15, 2004. Aura is designed to make comprehensive stratospheric and tropospheric composition measurements from ...its four instruments, the High Resolution Dynamics Limb Sounder (HIRDLS), the Microwave Limb Sounder (MLS), the Ozone Monitoring Instrument (OMI), and the Tropospheric Emission Spectrometer (TES). With the exception of HIRDLS, all of the instruments are performing as expected, and HIRDLS will likely be able to deliver most of their planned data products. We summarize the mission, instruments, and synergies in this paper.
Unprecedented Arctic ozone loss in 2011 Manney, Gloria L; Santee, Michelle L; Rex, Markus ...
Nature (London),
10/2011, Volume:
478, Issue:
7370
Journal Article
Peer reviewed
Chemical ozone destruction occurs over both polar regions in local winter-spring. In the Antarctic, essentially complete removal of lower-stratospheric ozone currently results in an ozone hole every ...year, whereas in the Arctic, ozone loss is highly variable and has until now been much more limited. Here we demonstrate that chemical ozone destruction over the Arctic in early 2011 was--for the first time in the observational record--comparable to that in the Antarctic ozone hole. Unusually long-lasting cold conditions in the Arctic lower stratosphere led to persistent enhancement in ozone-destroying forms of chlorine and to unprecedented ozone loss, which exceeded 80 per cent over 18-20 kilometres altitude. Our results show that Arctic ozone holes are possible even with temperatures much milder than those in the Antarctic. We cannot at present predict when such severe Arctic ozone depletion may be matched or exceeded.
The net mass flux from the stratosphere to the troposphere can be computed from the heating rate along the 380 K isentropic surface and the time rate of change of the mass of the lowermost ...stratosphere (the region between the tropopause and the 380 K isentrope) following Appenzeller et al. 1996. Given this net mass flux and the cross‐tropopause diabatic mass flux, the residual adiabatic mass flux across the tropopause can also be estimated. These fluxes have been computed using meteorological fields from a free‐running general circulation model (the finite volume general circulation model) and two assimilated data sets, finite volume data assimilation system (FVDAS), and UK Met Office (UKMO). All of the calculations agree that the annual average net mass flux for the Northern Hemisphere is about 1010 kg/s. There is less agreement on the Southern Hemisphere flux that might be half as large. For all three data sets the adiabatic mass flux is from the upper troposphere into the lowermost stratosphere. This adiabatic flux into the lowermost stratosphere is roughly 5 times larger than the diabatic mass flux into the stratosphere across the tropical tropopause. For the FVDAS the midlatitude tropopause diabatic flux is smaller than UKMO, apparently due to a systematically colder, higher FVDAS tropopause. Both data assimilation systems have a warmer, lower midlatitude tropopause compared to radiosondes, so the mass flux estimates can be considered upper bounds. Finally, we note that the difference in the diabatic mass fluxes between the two assimilated meteorological analyses is much larger than the interannual variability in either.
We use our forward domain filling trajectory model to explore the impact of tropical convection on stratospheric water vapor (H2O) and tropical tropopause layer cloud fraction (TTLCF). Our model ...results are compared to winter 2008/2009 TTLCF derived from Cloud‐Aerosol Lidar with Orthogonal Polarization and lower stratospheric H2O observations from the Microwave Limb Sounder. Convection alters the in situ water vapor by driving the air toward ice saturation relative humidity. If the air is subsaturated, then convection hydrates the air through the evaporation of ice, but if the air is supersaturated, then convective ice crystals grow and precipitate, dehydrating the air. On average, there are a large number of both hydrating and dehydrating convective events in the upper troposphere, but hydrating events exceed dehydrating events. Explicitly adding convection produces a less than 2% increase in global stratospheric water vapor during the period analyzed here. Tropical tropopause temperature is the primary control of stratospheric water vapor, and unless convection extends above the tropopause, it has little direct impact. Less than 1% of the model parcels encounter convection above the analyzed cold‐point tropopause. Convection, on the other hand, has a large impact on TTLCF. The model TTLCF doubles when convection is included, and this sensitivity has implications for the future climate‐related changes, given that tropical convective frequency and convective altitudes may change.
Plain Language Summary
Deep convection has been invoked as a significant source for stratospheric water vapor based on aircraft observations. This modelling study shows that deep convection plays almost no role in directly hydrating the stratosphere because deep convection rarely penetrates the tropopause 'cold trap' that largely controls stratospheric water vapor.
Key Points
Tropical convection increases stratospheric water vapor, but by less than 2%
Only convection that penetrates the tropical tropopause significantly impacts stratospheric water
Tropical convection is a major source of upper tropospheric clouds
The Tropical Composition, Cloud and Climate Coupling Experiment (TC4), was based in Costa Rica and Panama during July and August 2007. The NASA ER‐2, DC‐8, and WB‐57F aircraft flew 26 science flights ...during TC4. The ER‐2 employed 11 instruments as a remote sampling platform and satellite surrogate. The WB‐57F used 25 instruments for in situ chemical and microphysical sampling in the tropical tropopause layer (TTL). The DC‐8 used 25 instruments to sample boundary layer properties, as well as the radiation, chemistry, and microphysics of the TTL. TC4 also had numerous sonde launches, two ground‐based radars, and a ground‐based chemical and microphysical sampling site. The major goal of TC4 was to better understand the role that the TTL plays in the Earth's climate and atmospheric chemistry by combining in situ and remotely sensed data from the ground, balloons, and aircraft with data from NASA satellites. Significant progress was made in understanding the microphysical and radiative properties of anvils and thin cirrus. Numerous measurements were made of the humidity and chemistry of the tropical atmosphere from the boundary layer to the lower stratosphere. Insight was also gained into convective transport between the ground and the TTL, and into transport mechanisms across the TTL. New methods were refined and extended to all the NASA aircraft for real‐time location relative to meteorological features. The ability to change flight patterns in response to aircraft observations relayed to the ground allowed the three aircraft to target phenomena of interest in an efficient, well‐coordinated manner.
The impact of high‐frequency gravity waves on homogeneous‐freezing ice nucleation in cold cirrus clouds is examined using parcel model simulations driven by superpressure balloon measurements of ...temperature variability experienced by air parcels in the tropical tropopause region. We find that the primary influence of high‐frequency waves is to generate rapid cooling events that drive production of numerous ice crystals. Quenching of ice nucleation events by temperature tendency reversal in the highest‐frequency waves does occasionally produce low ice concentrations, but the overall impact of high‐frequency waves is to increase the occurrence of high ice concentrations. The simulated ice concentrations are considerably higher than indicated by in situ measurements of cirrus in the tropical tropopause region. One‐dimensional simulations suggest that although sedimentation reduces mean ice concentrations, a discrepancy of about a factor of 3 with observed ice concentrations remains. Reconciliation of numerical simulations with the observed ice concentrations will require inclusion of physical processes such as heterogeneous nucleation and entrainment.
Key Points
High‐frequency waves primarily result in high ice concentrations
Ice nucleation quenching by high‐frequency waves has a minor impact on ice concentrations
Homogeneous freezing results in ice concentrations exceeding observed values
Stratosphere-troposphere exchange of mass and ozone Olsen, Mark A.; Schoeberl, Mark R.; Douglass, Anne R.
Journal of Geophysical Research - Atmospheres,
27 December 2004, Volume:
109, Issue:
D24
Journal Article
Peer reviewed
Open access
This study examines the relationship between the extratropical cross‐tropopause fluxes of mass and ozone. The adiabatic and diabatic components of the net fluxes are also compared. The rate of change ...of mass in the lowermost stratosphere and the flux across the 380 K isentropic surface are used to determine the net tropopause mass flux in the framework of a global circulation model. The diabatic mass flux is calculated from the heating rate at the tropopause, and the adiabatic component is determined by the difference of the net and diabatic fluxes. Consistent ozone fields are obtained by driving the Goddard Chemistry and Transport Model with meteorological output of the global circulation model for the same years. The ozone flux is determined by convolving the mass flux and ozone mixing ratio. The results show the following: (1) The seasonal cycle of the ozone mixing ratio is out of phase with the transport cycle leading to a temporal offset of the mass and ozone fluxes; (2) the downward net diabatic flux of mass and ozone occurs primarily at middle latitudes while the adiabatic mass flux is dominated by troposphere‐to‐stratosphere transport at higher latitudes; and (3) the Southern Hemisphere stratospheric vortex is more effective at blocking meridional transport, resulting in a phase difference of mean tropopause ozone mixing ratio in the higher Southern Hemisphere latitudes with respect to the corresponding Northern Hemisphere season and location. Finally, this study suggests that individual pathways of cross‐tropopause transport are unlikely to be the result of simultaneous adiabatic and diabatic mechanisms.
We have analyzed 13 years (1993–2005) of tropical stratospheric water vapor data from the Halogen Occultation Experiment and over 3 years of data (October 2004 through November 2007) from the Aura ...Microwave Limb Sounder. By correlating the phase lag of the water vapor “tape recorder” signal between levels we estimate the time mean vertical velocity. Our estimated vertical velocity compares well with calculations from the Goddard Earth Observing System (GEOS) chemistry‐climate model (CCM) and from the GEOS data assimilation system. Between 18 and 26 km both the GEOS CCM simulations and water vapor observations agree that the vertical velocity is below 0.04 cm/s, with a minimum near 20 km of 0.03 cm/s. Vertical velocities deduced from water vapor observations are higher than those from the GEOS CCM in the region 16–18 km (0.04 cm/s) and above 26–30 km (up to 0.07 cm/s). These estimates are close to earlier estimates from a shorter water vapor record and radiative transfer models. No evidence is found for velocities as high as 0.15 cm/s as was recently estimated from aircraft CO2 measurements in the upper troposphere/lower stratosphere. Further diagnosis of the aircraft CO2 data and model simulations of CO2 show that while the CO2 data give an apparent upward transport velocity of ∼0.06 cm/s, about half of this is due to vertical and horizontal eddy transport. Accounting for the eddy terms gives a CO2‐based estimate of the vertical velocity of ∼0.03 cm/s, in much closer agreement with that estimated from water vapor.
We use kinematic and diabatic back trajectory calculations, driven by winds from a general circulation model (GCM) and two different data assimilation systems (DAS), to compute the age spectrum at ...three latitudes in the lower stratosphere. The age spectra are compared to chemical transport model (CTM) calculations, and the mean ages from all of these studies are compared to observations. The age spectra computed using the GCM winds show a reasonably isolated tropics, in good agreement with observations; however, the age spectra determined from the DAS differ from the GCM spectra. For the DAS diabatic trajectory calculations there is too much exchange between the tropics and midlatitudes. The age spectrum is thus too broad, and the tropical mean age is too old as a result of mixing older midlatitude air with tropical air. Likewise, the midlatitude mean age is too young because of the in‐mixing of tropical air. The DAS kinematic trajectory calculations show excessive vertical dispersion of parcels in addition to excessive exchange between the tropics and midlatitudes. Because air is moved rapidly to the troposphere from the vertical dispersion, the age spectrum is shifted toward the young side. The excessive vertical and meridional dispersion compensate in the kinematic case, giving a reasonable tropical mean age. The CTM calculation of the age spectrum using the DAS winds shows the same vertical and meridional dispersive characteristics of the kinematic trajectory calculation. These results suggest that the current DAS products will not give realistic trace gas distributions for long integrations; they also help explain why the extratropical mean ages determined in a number of previous DAS‐driven CTMs are too young compared with observations. Finally, we note that trajectory‐generated age spectra show significant age anomalies correlated with the seasonal cycles. These anomalies can be linked to year‐to‐year variations in the tropical heating rate. The anomalies are suppressed in the CTM spectra, suggesting that the CTM transport scheme is too diffusive.
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