318 research outputs found
Revising the retrieval technique of a long-term stratospheric HNO3 data set: from a constrained matrix inversion to the optimal estimation algorithm
The Ground-Based Millimeter-wave Spectrometer
(GBMS) was designed and built at the State University
of New York at Stony Brook in the early 1990s and since
then has carried out many measurement campaigns of stratospheric
O3, HNO3, CO and N2O at polar and mid-latitudes.
Its HNO3 data set shed light on HNO3 annual cycles over
the Antarctic continent and contributed to the validation of
both generations of the satellite-based JPL Microwave Limb
Sounder (MLS). Following the increasing need for long-term
data sets of stratospheric constituents, we resolved to establish
a long-term GMBS observation site at the Arctic station
of Thule (76.5 N, 68.8 W), Greenland, beginning in January
2009, in order to track the long- and short-term interactions
between the changing climate and the seasonal processes
tied to the ozone depletion phenomenon. Furthermore,
we updated the retrieval algorithm adapting the Optimal
Estimation (OE) method to GBMS spectral data in order
to conform to the standard of the Network for the Detection
of Atmospheric Composition Change (NDACC) microwave
group, and to provide our retrievals with a set of averaging
kernels that allow more straightforward comparisons with
other data sets. The new OE algorithm was applied to GBMS
HNO3 data sets from 1993 South Pole observations to date,
in order to produce HNO3 version 2 (v2) profiles. A sample
of results obtained at Antarctic latitudes in fall and winter
and at mid-latitudes is shown here. In most conditions, v2
inversions show a sensitivity (i.e., sum of column elements
of the averaging kernel matrix) of 100±20% from 20 to
45 km altitude, with somewhat worse (better) sensitivity in
the Antarctic winter lower (upper) stratosphere. The 1 uncertainty
on HNO3 v2 mixing ratio vertical profiles depends on altitude and is estimated at 15% or 0.3 ppbv, whichever
is larger. Comparisons of v2 with former (v1) GBMS HNO3
vertical profiles, obtained employing the constrained matrix
inversion method, show that v1 and v2 profiles are overall
consistent. The main difference is at the HNO3 mixing ratio
maximum in the 20â25 km altitude range, which is smaller
in v2 than v1 profiles by up to 2 ppbv at mid-latitudes and
during the Antarctic fall. This difference suggests a better
agreement of GBMS HNO3 v2 profiles with both UARS/ and
EOS Aura/MLS HNO3 data than previous v1 profiles
On the cryogenic removal of NOy from the Antarctic polar stratosphere
We review current knowledge about the annual cycle of transport of nitrogen oxides to, and removal from, the
polar stratosphere, with particular attention to Antarctica where the annual winter denitrifi cation process is both
regular in occurrence and severe in effect. Evidence for a large downward fl ux of NOy from the mesosphere to
the stratosphere, fi rst seen briefl y in the Limb Infrared Monitor of the Stratosphere (LIMS) data from the Arctic
winter of 1978-1979, has been found during the 1990s in both satellite and ground-based observations, though this
still seems to be omitted from many atmospheric models. When incorporated in the Stony Brook- St. Petersburg
two dimensional (2D) transport and chemistry model, more realistic treatment of the NOy fl ux, along with sulfate
transport from the mesosphere, sulfate aerosol formation where temperature is favorable, and the inclusion of a
simple ion-cluster reaction, leads to good agreement with observed HNO3 formation in the mid-winter middle to
upper stratosphere. To further emphasize the importance of large fl uxes of thermospheric and mesospheric NOy
into the polar stratosphere, we have used observations, supplemented with model calculations, to defi ne new
altitude dependent correlation curves between N2O and NOy. These are more suitable than those previously used
in the literature to represent conditions within the Antarctic vortex region prior to and during denitrifi cation by
Polar Stratospheric Cloud (PSC) particles. Our NOy -N2O curves lead to a 40% increase in the average amount
of NOy removed during the Antarctic winter with respect to estimates calculated using NOy-N2O curves from the
Atmospheric Trace Molecule Spectroscopy (ATMOS)/ATLAS-3 data set
Binary reaction decays from 24Mg+12C
Charged particle and gamma decays in 24Mg* are investigated for excitation
energies where quasimolecular resonances appear in 12C+12C collisions. Various
theoretical predictions for the occurence of superdeformed and hyperdeformed
bands associated with resonance structures with low spin are discussed within
the measured 24Mg* excitation energy region. The inverse kinematics reaction
24Mg+12C is studied at E_lab(24Mg) = 130 MeV, an energy which enables the
population of 24Mg states decaying into 12C+12C resonant break-up states.
Exclusive data were collected with the Binary Reaction Spectrometer in
coincidence with EUROBALL IV installed at the VIVITRON Tandem facility at
Strasbourg. Specific structures with large deformation were selectively
populated in binary reactions and their associated gamma decays studied.
Coincident events associated with inelastic and alpha-transfer channels have
been selected by choosing the excitation energy or the entry point via the
two-body Q-values. The analysis of the binary reaction channels is presented
with a particular emphasis on 24Mg-gamma, 20Ne-gamma and 16O-gamma
coincidences. New information (spin and branching ratios) is deduced on
high-energy states in 24Mg and 16O, respectively.Comment: 27 pages, 8 figures, 1 tabl
Evolution of temperature, O3, CO, and N2O profiles during the exceptional 2009 Arctic major stratospheric warming as observed by lidar and mm-wave spectroscopy at Thule (76.5°N, 68.8°W), Greenland.
The 2009 Arctic sudden stratospheric warming (SSW) was the most intense event of this kind ever observed. Unique ground-based measurements of middle atmospheric profiles for temperature, O3, CO, and N2O obtained at Thule (76.5°N, 68.8°W), Greenland, in the period January â early March are used to show the evolution of the 2009 SSW in the region of its maximum intensity. The first sign of the SSW was detected at Ξ~2000 K on January 19, when a rapid decrease in CO mixing ratio took place. The first evidence of a temperature increase was observed at the same level on 22 January, the earliest date on which lidar measurements reached above ~50 km. The warming propagated from the upper to the lower stratosphere in 7 days and the record maximum temperature of 289 K was observed between 1300 and 1500 K potential temperature on 22 January. A strong vortex splitting was associated with the SSW. Stratospheric backward trajectories indicate that airmasses arriving to Thule during the warming peak underwent a rapid compression and an intense adiabatic warming of up to 50 K. The rapid advection of air from the extra-tropics was also occasionally observed to produce elevated values of N2O mixing ratio. Starting from mid-February the temperature profile and the N2O mixing ratio returned to the pre-warming values in the mid and upper stratosphere, indicating the reformation of the vortex at these levels. In late winter, vertical descent from starting altitudes of ~60 km is estimated from CO profiles to be 0.25±0.05 km/day
Millimeter wave spectroscopic measurements of stratospheric and mesospheric constituents over the Italian Alps: stratospheric ozone
Measurements of rotational lines emitted by middle atmospheric trace gases have been carried out from the Alpine
station of Testa Grigia (45.9°N, 7.7°E, elev. 3500 m) by means of a Ground-Based Millimeter-wave Spectrometer
(GBMS). Observations of species such as O3, HNO3, CO, N2O, HCN, and HDO took place during 4 winter periods,
from February 2004 to March 2007, for a total of 116 days of measurements grouped in about 18 field campaigns.
By studying the pressure-broadened shape of emission lines the vertical distribution of the observed constituents
is retrieved within an altitude range of âŒ17-75 km, constrained by the 600 MHz pass band and the 65 kHz
spectral resolution of the back-end spectrometer. This work discusses the behavior of stratospheric O3 during the
entire period of operation at Testa Grigia. Mid-latitude O3 columnar content as estimated using GBMS measurements
can vary by large amounts over a period of very few days, with the largest variations observed in December
2005, February 2006, and March 2006, confirming that the northern winter of 2005-2006 was characterized by a
particularly intense planetary wave activity. The largest rapid variation from maximum to minimum O3 column values
over Testa Grigia took place in December 2006 and reached a relative value of 72% with respect to the average
column content for that period. During most GBMS observation times much of the variability is concentrated
in the column below 20 km, with tropospheric weather systems and advection of tropical tropospheric air into the
lower stratosphere over Testa Grigia having a large impact on the observed variations in column contents. Nonetheless,
a wide variability is also found in middle stratospheric GBMS O3 measurements, as expected for mid-latitude
ozone. We find that O3 mixing ratios at âŒ32 km are very well correlated with the solar illumination experienced by
air masses over the previous âŒ15 days, showing that already at 32 km altitude ozone photochemistry dominates over
transport processes. The correlation of lower stratospheric ozone concentrations with potential vorticity as an indicator
of transport is instead not as clear-cut, due to very complex mixing processes that characterize stratospheric
air at mid-latitudes. Correlations of O3 over Testa Grigia with stratospheric tracers such as N2O and HCN, also observed
by means of the GBMS, are planned for the future, in order to better characterize lower stratospheric dynamics
and therefore lower stratospheric ozone concentrations at mid-latitudes
Validation of the Aura Microwave Limb Sounder HNOmeasurements
We assess the quality of the version 2.2 (v2.2) HNO3 measurements from the Microwave Limb Sounder (MLS) on the Earth Observing System Aura satellite. The MLS HNO3 product has been greatly improved over that in the previous version (v1.5), with smoother profiles, much more realistic behavior at the lowest retrieval levels, and correction of a high bias caused by an error in one of the spectroscopy files used in v1.5 processing. The v2.2 HNO3 data are scientifically useful over the range 215 to 3.2 hPa, with single-profile precision of âŒ0.7 ppbv throughout. Vertical resolution is 3â4 km in the upper troposphere and lower stratosphere, degrading to âŒ5 km in the middle and upper stratosphere. The impact of various sources of systematic uncertainty has been quantified through a comprehensive set of retrieval simulations. In aggregate, systematic uncertainties are estimated to induce in the v2.2 HNO3 measurements biases that vary with altitude between ±0.5 and ±2 ppbv and multiplicative errors of ±5â15% throughout the stratosphere, rising to âŒÂ±30% at 215 hPa. Consistent with this uncertainty analysis, comparisons with correlative data sets show that relative to HNO3 measurements from ground-based, balloon-borne, and satellite instruments operating in both the infrared and microwave regions of the spectrum, MLS v2.2 HNO3 mixing ratios are uniformly low by 10â30% throughout most of the stratosphere. Comparisons with in situ measurements made from the DC-8 and WB-57 aircraft in the upper troposphere and lowermost stratosphere indicate that the MLS HNO3 values are low in this region as well, but are useful for scientific studies (with appropriate averaging)
Spectrally resolved observations of atmospheric emitted radiance in the H2O rotation band
This paper presents the project Earth Cooling by Water
Vapor Radiation, an observational programme, which aims at
developing a database of spectrally resolved far infrared
observations, in atmospheric dry conditions, in order to
validate radiative transfer models and test the quality of water
vapor continuum and line parameters. The project provides
the very first set of far-infrared spectral downwelling
radiance measurements, in dry atmospheric conditions,
which are complemented with Raman Lidar-derived
temperature and water vapor profiles
Reaction mechanisms in 24Mg+12C and 32S+24Mg
The occurence of "exotic" shapes in light N=Z alpha-like nuclei is
investigated for 24Mg+12C and 32S+24Mg. Various approaches of superdeformed and
hyperdeformed bands associated with quasimolecular resonant structures with low
spin are presented. For both reactions, exclusive data were collected with the
Binary Reaction Spectrometer in coincidence with EUROBALL IV installed at the
VIVITRON Tandem facility of Strasbourg. Specific structures with large
deformation were selectively populated in binary reactions and their associated
-decays studied. The analysis of the binary and ternary reaction
channels is discussed.Comment: 7 pages, 4 figures, Paper presented at the Fusion08 International
Conference on New Aspects of Heavy Ion Collisions Near the Coulomb Barrier,
Chicago. Proceedings to be published by AIP Conference Proceedings Illinois,
USA, September 22-26, 200
Observations of surface radiation and stratospheric processes at Thule Air Base, Greenland, during the IPY
Ground-based measurements of atmospheric parameters have been carried
out for more than 20 years at the Network for the Detection of Atmospheric
Composition Change (NDACC) station at Thule Air Base
(76.5°N, 68.8°W), on the north-western coast of Greenland. Various instruments
dedicated to the study of the lower and middle polar atmosphere
are installed at Thule in the framework of a long standing
collaboration among Danish, Italian, and US research institutes and universities.
This effort aims at monitoring the composition, structure and
dynamics of the polar stratosphere, and at studying the Arctic energy
budget and the role played by different factors, such as aerosols, water
vapour, and surface albedo. During the International Polar Year (IPY),
in winter 2008-2009, an intensive measurement campaign was conducted
at Thule within the framework of the IPY project âOzone layer and UV
radiation in a changing climate evaluated during IPYâ (ORACLE-O3)
which sought to improve our understanding of the complex mechanisms
that lead to the Arctic stratospheric O3 depletion. The campaign involved
a lidar system, measuring aerosol backscatter and depolarization ratios
up to 35 km and atmospheric temperature profiles from 25 to 70 km altitude,
a ground-based millimeter-wave spectrometer (GBMS) used to derive
stratospheric mixing ratio profiles of different chemical species
involved in the stratospheric ozone depletion cycle, and then ground-based
radiometers and a Cimel sunphotometer to study the Arctic radiative
budget at the surface. The observations show that the surface radiation
budget is mainly regulated by the longwave component throughout most
of the year. Clouds have a significant impact contributing to enhance the
role of longwave radiation. Besides clouds, water vapour seasonal changes produce the largest modification in the shortwave component at the surface,
followed by changes in surface albedo and in aerosol amounts. For
what concerns the middle atmosphere, during the first part of winter
2008-2009 the cold polar vortex allowed for the formation of polar stratospheric
clouds (PSCs) which were observed above Thule by means of the
lidar. This period was also characterized by GBMS measurements of low
values of O3 due to the catalytic reactions prompted by the PSCs. In mid-
January, as the most intense Sudden Stratospheric Warming event ever
observed in the Arctic occurred, GBMS and lidar measurements of O3,
N2O, CO and temperature described its evolution as it propagated from
the upper atmosphere to the lower stratosphere
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