74 research outputs found
Profiles of CH_4, HDO, H_2O, and N_2O with improved lower tropospheric vertical resolution from Aura TES radiances
Thermal infrared (IR) radiances measured near 8 microns contain information about the vertical distribution of water vapor (H_2O), the water isotopologue HDO, and methane (CH_4), key gases in the water and carbon cycles. Previous versions (Version 4 or less) of the TES profile retrieval algorithm used a "spectral-window" approach to minimize uncertainty from interfering species at the expense of reduced vertical resolution and sensitivity. In this manuscript we document changes to the vertical resolution and uncertainties of the TES version 5 retrieval algorithm. In this version (Version 5), joint estimates of H_2O, HDO, CH_4 and nitrous oxide (N_2O) are made using radiances from almost the entire spectral region between 1100 cm^(−1) and 1330 cm^(−1). The TES retrieval constraints are also modified in order to better use this information. The new H_2O estimates show improved vertical resolution in the lower troposphere and boundary layer, while the new HDO/H_2O estimates can now profile the HDO/H_2O ratio between 925 hPa and 450 hPa in the tropics and during summertime at high latitudes. The new retrievals are now sensitive to methane in the free troposphere between 800 and 150 mb with peak sensitivity near 500 hPa; whereas in previous versions the sensitivity peaked at 200 hPa. However, the upper troposphere methane concentrations are biased high relative to the lower troposphere by approximately 4% on average. This bias is likely related to temperature, calibration, and/or methane spectroscopy errors. This bias can be mitigated by normalizing the CH_4 estimate by the ratio of the N_2O estimate relative to the N_2O prior, under the assumption that the same systematic error affects both the N_2O and CH_4 estimates. We demonstrate that applying this ratio theoretically reduces the CH4 estimate for non-retrieved parameters that jointly affect both the N_2O and CH_4 estimates. The relative upper troposphere to lower troposphere bias is approximately 2.8% after this bias correction. Quality flags based upon the vertical variability of the methane and N_2O estimates can be used to reduce this bias further. While these new CH_4, HDO/H_2O, and H_2O estimates are consistent with previous TES retrievals in the altitude regions where the sensitivities overlap, future comparisons with independent profile measurement will be required to characterize the biases of these new retrievals and determine if the calculated uncertainties using the new constraints are consistent with actual uncertainties
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Validation of TES Methane with HIPPO Aircraft Observations: Implications for Inverse Modeling of Methane Sources
We validate satellite methane observations from the Tropospheric Emission Spectrometer (TES) with 151 aircraft vertical profiles over the Pacific from the HIAPER Pole-to-Pole Observation (HIPPO) program. We find that a collocation window of ±750 km and ±24 h does not introduce significant error in comparing TES and aircraft profiles. We validate both the TES standard product (V004) and an experimental product with two pieces of information in the vertical (V005). We determine a V004 mean bias of 65.8 ppb and random instrument error of 43.3 ppb. For V005 we determine a mean bias of 42.3 ppb and random instrument error of 26.5 ppb in the upper troposphere, and mean biases (random instrument errors) in the lower troposphere of 28.8 (28.7) and 16.9 (28.9) ppb at high and low latitudes respectively. Even when V005 cannot retrieve two pieces of information it still performs better than V004. An observation system simulation experiment (OSSE) with the GEOS-Chem chemical transport model (CTM) and its adjoint shows that TES V004 has only limited value for constraining methane sources. Our successful validation of V005 encourages its production as a standard retrieval to replace V004.Earth and Planetary Science
Heterotic compactifications on SU(2)-structure backgrounds
In this paper we study the reduction of heterotic string theory on
SU(2)-structure backgrounds. We compute the bosonic low-energy gauged N=2
supergravity specified by the Killing vectors corresponding to the gauged
isometries. We check that the obtained Lagrangian is consistent with the one of
N=2 local supersymmetry. We also determine the Killing prepotentials.Comment: reference added, corrected typos and some factor
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Constraints on methane emissions in North America from future geostationary remote-sensing measurements
The success of future geostationary (GEO) satellite observation missions
depends on our ability to design instruments that address their key
scientific objectives. In this study, an Observation System Simulation
Experiment (OSSE) is
performed to quantify the constraints on methane (CH4) emissions in North
America obtained from shortwave infrared (SWIR), thermal infrared (TIR), and
multi-spectral (SWIR+TIR) measurements in geostationary orbit and from
future SWIR low-Earth orbit (LEO) measurements. An efficient stochastic
algorithm is used to compute the information content of the inverted
emissions at high spatial resolution (0.5° × 0.7°)
in a variational framework using the GEOS-Chem chemistry-transport model and
its adjoint. Our results show that at sub-weekly timescales, SWIR
measurements in GEO orbit can constrain about twice as many independent flux
patterns than in LEO orbit, with a degree of freedom for signal (DOF) for the
inversion of 266 and 115, respectively. Comparisons between TIR GEO and SWIR
LEO configurations reveal that poor boundary layer sensitivities for the TIR
measurements cannot be compensated for by the high spatiotemporal sampling of
a GEO orbit. The benefit of a multi-spectral instrument compared to current
SWIR products in a GEO context is shown for sub-weekly timescale constraints,
with an increase in the DOF of about 50 % for a 3-day inversion. Our
results further suggest that both the SWIR and multi-spectral measurements on
GEO orbits could almost fully resolve CH4 fluxes at a spatial resolution
of at least 100 km × 100 km over source hotspots (emissions
> 4 × 105 kg day−1). The sensitivity of the optimized
emission scaling factors to typical errors in boundary and initial conditions
can reach 30 and 50 % for the SWIR GEO or SWIR LEO configurations,
respectively, while it is smaller than 5 % in the case of a multi-spectral
GEO system. Overall, our results demonstrate that multi-spectral measurements
from a geostationary satellite platform would address the need for higher
spatiotemporal constraints on CH4 emissions while greatly mitigating the
impact of inherent uncertainties in source inversion methods on the inferred
fluxes
Asymmetric Orbifolds, Non-Geometric Fluxes and Non-Commutativity in Closed String Theory
In this paper we consider a class of exactly solvable closed string flux
backgrounds that exhibit non-commutativity in the closed string coordinates.
They are realized in terms of freely-acting asymmetric Z_N-orbifolds, which are
themselves close relatives of twisted torus fibrations with elliptic
Z_N-monodromy (elliptic T-folds). We explicitly construct the modular invariant
partition function of the models and derive the non-commutative algebra in the
string coordinates, which is exact to all orders in {\alpha}'. Finally, we
relate these asymmetric orbifold spaces to inherently stringy Scherk-Schwarz
backgrounds and non-geometric fluxes.Comment: 30 page
T-duality in the weakly curved background
We consider the closed string propagating in the weakly curved background
which consists of constant metric and Kalb-Ramond field with infinitesimally
small coordinate dependent part. We propose the procedure for constructing the
T-dual theory, performing T-duality transformations along coordinates on which
the Kalb-Ramond field depends. The obtained theory is defined in the
non-geometric double space, described by the Lagrange multiplier and
its -dual . We apply the proposed T-duality procedure to the
T-dual theory and obtain the initial one. We discuss the standard relations
between T-dual theories that the equations of motion and momenta modes of one
theory are the Bianchi identities and the winding modes of the other
Hypermoduli Stabilization, Flux Attractors, and Generating Functions
We study stabilization of hypermoduli with emphasis on the effects of
generalized fluxes. We find a class of no-scale vacua described by ISD
conditions even in the presence of geometric flux. The associated flux
attractor equations can be integrated by a generating function with the
property that the hypermoduli are determined by a simple extremization
principle. We work out several orbifold examples where all vector moduli and
many hypermoduli are stabilized, with VEVs given explicitly in terms of fluxes.Comment: 45 pages, no figures; Version submitted to JHE
Nongeometric Flux Compactifications
We investigate a simple class of type II string compactifications which
incorporate nongeometric "fluxes" in addition to "geometric flux" and the usual
H-field and R-R fluxes. These compactifications are nongeometric analogues of
the twisted torus. We develop T-duality rules for NS-NS geometric and
nongeometric fluxes, which we use to construct a superpotential for the
dimensionally reduced four-dimensional theory. The resulting structure is
invariant under T-duality, so that the distribution of vacua in the IIA and IIB
theories is identical when nongeometric fluxes are included. This gives a
concrete framework in which to investigate the possibility that generic string
compactifications may be nongeometric in any duality frame. The framework
developed in this paper also provides some concrete hints for how mirror
symmetry can be generalized to compactifications with arbitrary H-flux, whose
mirrors are generically nongeometric.Comment: 26 pages, JHEP3. v3: references, minor corrections, and
clarifications added. v4: sign correcte
Type IIA orientifold compactification on SU(2)-structure manifolds
We investigate the effective theory of type IIA string theory on
six-dimensional orientifold backgrounds with SU(2)-structure. We focus on the
case of orientifolds with O6-planes, for which we compute the bosonic effective
action in the supergravity approximation. For a generic SU(2)-structure
background, we find that the low-energy effective theory is a gauged N=2
supergravity where moduli in both vector and hypermultiplets are charged. Since
all these supergravities descend from a corresponding N=4 background, their
scalar target space is always a quotient of a SU(1,1)/U(1) x
SO(6,n)/SO(6)xSO(n) coset, and is therefore also very constrained.Comment: 31 pages; v2: local report number adde
SENTENCING MATTERS - FACTORS DETERMINING SENTENCE TYPE AND LENGTH: AN EXPLORATORY VIGNETTE STUDY
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