767 research outputs found
Atomic emission in the ultraviolet nightglow
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95222/1/grl4575.pd
CHEM2D-OPP: A new linearized gas-phase ozone photochemistry parameterization for high-altitude NWP and climate models
The new CHEM2D-Ozone Photochemistry Parameterization (CHEM2D-OPP) for high-altitude numerical weather prediction (NWP) systems and climate models specifies the net ozone photochemical tendency and its sensitivity to changes in ozone mixing ratio, temperature and overhead ozone column based on calculations from the CHEM2D interactive middle atmospheric photochemical transport model. We evaluate CHEM2D-OPP performance using both short-term (6-day) and long-term (1-year) stratospheric ozone simulations with the prototype high-altitude NOGAPS-ALPHA forecast model. An inter-comparison of NOGAPS-ALPHA 6-day ozone hindcasts for 7 February 2005 with ozone photochemistry parameterizations currently used in operational NWP systems shows that CHEM2D-OPP yields the best overall agreement with both individual Aura Microwave Limb Sounder ozone profile measurements and independent hemispheric (10°–90° N) ozone analysis fields. A 1-year free-running NOGAPS-ALPHA simulation using CHEM2D-OPP produces a realistic seasonal cycle in zonal mean ozone throughout the stratosphere. We find that the combination of a model cold temperature bias at high latitudes in winter and a warm bias in the CHEM2D-OPP temperature climatology can degrade the performance of the linearized ozone photochemistry parameterization over seasonal time scales despite the fact that the parameterized temperature dependence is weak in these regions
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Persistence of upper stratospheric wintertime tracer variability into the Arctic spring and summer
Using data from the Aeronomy of Ice in the Mesosphere (AIM) and Aura
satellites, we have categorized the interannual variability of winter- and
springtime upper stratospheric methane (CH4). We further show the effects
of this variability on the chemistry of the upper stratosphere throughout the
following summer. Years with strong wintertime mesospheric descent followed
by dynamically quiet springs, such as 2009, lead to the lowest summertime
CH4. Years with relatively weak wintertime descent, but strong springtime
planetary wave activity, such as 2011, have the highest summertime CH4. By
sampling the Aura Microwave Limb Sounder (MLS) according to the occultation
pattern of the AIM Solar Occultation for Ice Experiment (SOFIE), we show that
summertime upper stratospheric chlorine monoxide (ClO) almost perfectly
anticorrelates with the CH4. This is consistent with the reaction of
atomic chlorine with CH4 to form the reservoir species, hydrochloric acid
(HCl). The summertime ClO for years with strong, uninterrupted mesospheric
descent is about 50 % greater than in years with strong horizontal
transport and mixing of high CH4 air from lower latitudes. Small, but
persistent effects on ozone are also seen such that between 1 and 2 hPa, ozone
is about 4–5 % higher in summer for the years with the highest CH4
relative to the lowest. This is consistent with the role of the chlorine
catalytic cycle on ozone. These dependencies may offer a means to monitor
dynamical effects on the high-latitude upper stratosphere using summertime
ClO measurements as a proxy. Additionally, these chlorine-controlled ozone decreases,
which are seen to maximize after years with strong uninterrupted wintertime
descent, represent a new mechanism by which mesospheric descent can affect
polar ozone. Finally, given that the effects on ozone appear to persist much
of the rest of the year, the consideration of winter/spring dynamical
variability may also be relevant in studies of ozone trends
Assimilation of stratospheric and mesospheric temperatures from MLS and SABER into a global NWP model
International audienceThe forecast model and three-dimensional variational data assimilation components of the Navy Operational Global Atmospheric Prediction System (NOGAPS) have each been extended into the upper stratosphere and mesosphere to form an Advanced Level Physics High Altitude (ALPHA) version of NOGAPS extending to ~100 km. This NOGAPS-ALPHA NWP prototype is used to assimilate stratospheric and mesospheric temperature data from the Microwave Limb Sounder (MLS) and the Sounding of the Atmosphere using Broadband Radiometry (SABER) instruments. A 60-day analysis period in January and February, 2006, was chosen that includes a well documented stratospheric sudden warming. SABER temperatures indicate that the SSW caused the polar winter stratopause at ~40 km to disappear, then reform at ~80 km altitude and slowly descend during February. The NOGAPS-ALPHA analysis reproduces this observed stratospheric and mesospheric temperature structure, as well as realistic evolution of zonal winds, residual velocities, and Eliassen-Palm fluxes that aid interpretation of the vertically deep circulation and eddy flux anomalies that developed in response to this wave-breaking event. The observation minus forecast (O-F) standard deviations for MLS and SABER are ~2 K in the mid-stratosphere and increase monotonically to about 6 K in the upper mesosphere. Increasing O-F standard deviations in the mesosphere are expected due to increasing instrument error and increasing geophysical variance at small spatial scales in the forecast model. In the mid/high latitude winter regions, 10-day forecast skill is improved throughout the upper stratosphere and mesosphere when the model is initialized using the high-altitude analysis based on assimilation of both SABER and MLS data
Results from two years of ozone data taken with a new, ground-based microwave instrument: An overview
An overview of two years of data obtained with a ground-based microwave instrument is given. Intercomparisons with data obtained by the co-located JPL lidar and by SAGE 2 during near overpasses of the site are discussed, as are comparisons with mesospheric data taken earlier by SME and LIMS. Observations of diurnal variations of mesospheric ozone are shown
Version 1.3 AIM SOFIE Measured Methane (CH4): Validation and Seasonal Climatology
The V1.3 methane (CH4) measured by the Aeronomy of Ice in the Mesosphere (AIM) Solar Occultation for Ice Experiment (SOFIE) instrument is validated in the vertical range of ~25–70 km. The random error for SOFIE CH4 is ~0.1–1% up to ~50 km and degrades to ~9% at ∼ 70 km. The systematic error remains at ~4% throughout the stratosphere and lower mesosphere. Comparisons with CH4 data taken by the SCISAT Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) and the Envisat Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) show an agreement within ~15% in the altitude range ~30–60 km. Below ~25 km SOFIE CH4 is systematically higher (≥20%), while above ~65 km it is lower by a similar percentage. The sign change from the positive to negative bias occurs between ~55 km and ~60 km (or ~40 km and ~45 km) in the Northern (or Southern) Hemisphere. Methane, H2O, and 2CH4 + H2O yearly differences from their values in 2009 are examined using SOFIE and MIPAS CH4 and the Aura Microwave Limb Sounder (MLS) measured H2O. It is concluded that 2CH4 + H2O is conserved with altitude up to an upper limit between ~35 km and ~50 km depending on the season. In summer this altitude is higher. In the Northern Hemisphere the difference relative to 2009 is the largest in late spring and the established difference prevails throughout summer and fall, suggesting that summer and fall are dynamically quiet. In both hemispheres during winter there are disturbances (with a period of ~1 month) that travel downward throughout the stratosphere with a speed similar to the winter descent. ©2016. American Geophysical Union
NRLMSIS 2.1: An Empirical Model of Nitric Oxide Incorporated Into MSIS
We have developed an empirical model of nitric oxide (NO) number density at altitudes from similar to 73 km to the exobase, as a function of altitude, latitude, day of year, solar zenith angle, solar activity, and geomagnetic activity. The model is part of the NRLMSIS (R) 2.1 empirical model of atmospheric temperature and species densities; this upgrade to NRLMSIS 2.0 consists solely of the addition of NO. MSIS 2.1 assimilates observations from six space-based instruments: UARS/HALOE, SNOE, Envisat/MIPAS, ACE/FTS, Odin/SMR, and AIM/SOFIE. We additionally evaluated the new model against independent extant NO data sets. In this paper, we describe the formulation and fitting of the model, examine biases between the data sets and model and among the data sets, compare with another empirical NO model (NOEM), and discuss scientific aspects of our analysis
NRLMSIS 2.1: An Empirical Model of Nitric Oxide Incorporated Into MSIS
We have developed an empirical model of nitric oxide (NO) number density at altitudes from ∼73 km to the exobase, as a function of altitude, latitude, day of year, solar zenith angle, solar activity, and geomagnetic activity. The model is part of the NRLMSIS® 2.1 empirical model of atmospheric temperature and species densities; this upgrade to NRLMSIS 2.0 consists solely of the addition of NO. MSIS 2.1 assimilates observations from six space-based instruments: UARS/HALOE, SNOE, Envisat/MIPAS, ACE/FTS, Odin/SMR, and AIM/SOFIE. We additionally evaluated the new model against independent extant NO data sets. In this paper, we describe the formulation and fitting of the model, examine biases between the data sets and model and among the data sets, compare with another empirical NO model (NOEM), and discuss scientific aspects of our analysis
Arterio-enteric fistula in failed enteric-drained pancreas transplants: an impending danger
Enteric drainage is the preferred method of exocrine diversion in simultaneous kidney-pancreas transplantation. Because of improvements in immunosuppression, enteric drainage has become the preferred method of pancreas transplantation in general. Although associated with less potential complications than bladder-drained pancreas, potentially lethal arterio-enteric fistulas in the setting of nonfunctioning allografts represent a constant threat. We herein present a case report, a review of the literature, and a call for caution
Inductive learning spatial attention
This paper investigates the automatic induction of spatial attention
from the visual observation of objects manipulated
on a table top. In this work, space is represented in terms of
a novel observer-object relative reference system, named Local
Cardinal System, defined upon the local neighbourhood
of objects on the table. We present results of applying the
proposed methodology on five distinct scenarios involving
the construction of spatial patterns of coloured blocks
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