Jet Propulsion Laboratory

About: Jet Propulsion Laboratory is a facility organization based out in La Cañada Flintridge, California, United States. It is known for research contribution in the topics: Mars Exploration Program & Telescope. The organization has 8801 authors who have published 14333 publications receiving 548163 citations. The organization is also known as: JPL & NASA JPL.

Global budget of methanol : Constraints from atmospheric observations

Abstract: factor of 3 higher for young than from mature leaves. The atmospheric lifetime of methanol in the model is 7 days; gas-phase oxidation by OH accounts for 63% of the global sink, dry deposition to land 26%, wet deposition 6%, uptake by the ocean 5%, and aqueous-phase oxidation in clouds less than 1%. The resulting simulation of atmospheric concentrations is generally unbiased in the Northern Hemisphere and reproduces the observed correlations of methanol with acetone, HCN, and CO in Asian outflow. Accounting for decreasing emission from leaves as they age is necessary to reproduce the observed seasonal variation of methanol concentrations at northern midlatitudes. The main model discrepancy is over the South Pacific, where simulated concentrations are a factor of 2 too low. Atmospheric production from the CH3O2 self-reaction is the dominant model source in this region. A factor of 2 increase in this source (to 50–100 Tg yr � 1 ) would largely correct the discrepancy and appears consistent with independent constraints on CH3O2 concentrations. Our resulting best estimate of the global source of methanol is 240 Tg yr � 1 . More observations of methanol concentrations and fluxes are needed over tropical continents. Better knowledge is needed of CH3O2 concentrations in the remote troposphere and of the underlying organic chemistry.

A High Spatial Resolution Analysis of the MAXIMA-1 Cosmic Microwave Background Anisotropy Data

Abstract: We extend the analysis of the MAXIMA-1 cosmic microwave background data to smaller angular scales. MAXIMA, a bolometric balloon-borne experiment, mapped a 124 deg2 region of the sky with 10' resolution at frequencies of 150, 240, and 410 GHz during its first flight. The original analysis, which covered the multipole range 36 ≤ l ≤ 785 using a 100 deg2 map, is extended to l = 1235 using a subset of the data from three 150 GHz photometers in the fully cross-linked central 60 deg2 of the map. The main improvement over the original analysis is the use of 3' square pixels in the calculation of the map. The new analysis is consistent with the original for l 785, where inflationary models predict a third acoustic peak, the new analysis shows power with an amplitude of 56 ± 7 μK at l 850 in excess to the average power of 42 ± 3 μK in the range 441 < l < 785.

A Herschel [CII] Galactic plane survey I: the global distribution of ISM gas components

Abstract: [Abridged] The [CII] 158um line is an important tool for understanding the life cycle of interstellar matter. Ionized carbon is present in a variety of phases of the interstellar medium, including the diffuse ionized medium, warm and cold atomic clouds, clouds in transition from atomic to molecular, and dense and warm photon dominated regions (PDRs). The Galactic Observations of Terahertz C+ (GOTC+) project surveys the [CII] line over the entire Galactic disk with velocity-resolved observations using the Herschel/HIFI instrument. We present the first longitude-velocity maps of the [CII] emission for Galactic latitudes b=0deg, +-0.5deg, and +-1.0deg. [CII] emission is mostly associated with spiral arms, mainly emerging from Galactocentric distances between 4 and 10 kpc. We estimate that most of the observed [CII] emission is produced by dense PDRs (47%), with smaller contributions from CO-dark H2 gas (28%), cold atomic gas (21%), and ionized gas (4%). Atomic gas inside the Solar radius is mostly in the form of cold neutral medium (CNM), while the warm neutral medium (WNM) gas dominates the outer galaxy. The average fraction of CNM relative to total atomic gas is 43%. We find that the warm and diffuse CO-dark H2 is distributed over a larger range of Galactocentric distances (4-11 kpc) than the cold and dense H2 gas traced by 12CO and 13CO (4-8kpc). The fraction of CO-dark H2 to total H2 increases with Galactocentric distance, ranging from 20% at 4 kpc to 80% at 10 kpc. On average, CO-dark H2 accounts for 30% of the molecular mass of the Milky Way. When the CO-dark H2 component is included, the radial distribution of the CO-to-H2 conversion factor is steeper than that when only molecular gas traced by CO is considered. Most of the observed [CII] emission emerging from dense PDRs is associated with modest far-ultraviolet fields in the range chi0~1-30.

The c2d Spitzer Spectroscopic Survey of Ices Around Low-Mass Young Stellar Objects: I. H2O and the 5-8 um Bands

Abstract: With the goal to study the physical and chemical evolution of ices in solar-mass systems, a spectral survey is conducted of a sample of 41 low luminosity YSOs using 3-38 um Spitzer and ground-based spectra. The long-known 6.0 and 6.85 um bands are detected toward all sources, with the Class 0-type YSOs showing the deepest bands ever observed. In almost all sources the 6.0 um band is deeper than expected from the bending mode of pure solid H2O. The depth and shape variations of the remaining 5-7 um absorption indicate that it consists of 5 independent components, which, by comparison to laboratory studies, must be from at least 8 different carriers. Simple species are responsible for much of the absorption in the 5-7 um region, at abundances of 1-30% for CH3OH, 3-8% for NH3, 1-5% for HCOOH, ~6% for H2CO, and ~0.3% for HCOO- with respect to solid H2O. The 6.85 um band likely consists of one or two carriers, of which one is less volatile than H2O because its abundance relative to H2O is enhanced at lower H2O/tau_9.7 ratios. It does not survive in the diffuse interstellar medium (ISM), however. The similarity of the 6.85 um bands for YSOs and background stars indicates that its carrier(s) must be formed early in the molecular cloud evolution. If an NH4+ salt is the carrier its abundance with respect to solid H2O is typically 7%, and low temperature acid-base chemistry or cosmic ray induced reactions must have been involved in its formation. Possible origins are discussed for the carrier of an enigmatic, very broad absorption between 5 and 8 um. Finally, all the phenomena observed for ices toward massive YSOs are also observed toward low mass YSOs, indicating that processing of the ices by internal ultraviolet radiation fields is a minor factor in the early chemical evolution of the ices. [abridged]