A network of 10 southern hemisphere tropical and subtropical stations, designated the Southern Hemisphere Additional Ozonesondes (SHADOZ) project and established from operational sites, provided over ...1000 ozone profiles during the period 1998–2000. Balloon‐borne electrochemical concentration cell (ECC) ozonesondes, combined with standard radiosondes for pressure, temperature, and relative humidity measurements, collected profiles in the troposphere and lower to midstratosphere at: Ascension Island; Nairobi, Kenya; Irene, South Africa; Réunion Island; Watukosek, Java; Fiji; Tahiti; American Samoa; San Cristóbal, Galapagos; and Natal, Brazil. The archived data are available at: 〈http://croc.gsfc.nasa.gov/shadoz〉.1 In this paper, uncertainties and accuracies within the SHADOZ ozone data set are evaluated by analyzing: (1) imprecisions in profiles and in methods of extrapolating ozone above balloon burst; (2) comparisons of column‐integrated total ozone from sondes with total ozone from the Earth‐Probe/Total Ozone Mapping Spectrometer (TOMS) satellite and ground‐based instruments; and (3) possible biases from station to station due to variations in ozonesonde characteristics. The key results are the following: (1) Ozonesonde precision is 5%. (2) Integrated total ozone column amounts from the sondes are usually to within 5% of independent measurements from ground‐based instruments at five SHADOZ sites and overpass measurements from the TOMS satellite (version 7 data). (3) Systematic variations in TOMS‐sonde offsets and in ground‐based‐sonde offsets from station to station reflect biases in sonde technique as well as in satellite retrieval. Discrepancies are present in both stratospheric and tropospheric ozone. (4) There is evidence for a zonal wave‐one pattern in total and tropospheric ozone, but not in stratospheric ozone.
We present high-resolution measurements of water vapour, aerosols and clouds in the Arctic stratosphere in January and February 2010 carried out by in situ instrumentation on balloon sondes and ...high-altitude aircraft combined with satellite observations. The measurements provide unparalleled evidence of dehydration and rehydration due to gravitational settling of ice particles. An extreme cooling of the Arctic stratospheric vortex during the second half of January 2010 resulted in a rare synoptic-scale outbreak of ice polar stratospheric clouds (PSCs) remotely detected by the lidar aboard the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) satellite. The widespread occurrence of ice clouds was followed by sedimentation and consequent sublimation of ice particles, leading to vertical redistribution of water inside the vortex. A sequence of balloon and aircraft soundings with chilled mirror and Lyman- α hygrometers (Cryogenic Frostpoint Hygrometer, CFH; Fast In Situ Stratospheric Hygrometer, FISH; Fluorescent Airborne Stratospheric Hygrometer, FLASH) and backscatter sondes (Compact Optical Backscatter Aerosol Detector, COBALD) conducted in January 2010 within the LAPBIAT (Lapland Atmosphere-Biosphere Facility) and RECONCILE (Reconciliation of Essential Process Parameters for an Enhanced Predictability of Arctic Stratospheric Ozone Loss and its Climate Interactions) campaigns captured various phases of this phenomenon: ice formation, irreversible dehydration and rehydration. Consistent observations of water vapour by these independent measurement techniques show clear signatures of irreversible dehydration of the vortex air by up to 1.6 ppmv in the 20–24 km altitude range and rehydration by up to 0.9 ppmv in a 1 km thick layer below. Comparison with space-borne Aura MLS (Microwave Limb Sounder) water vapour observations allow the spatiotemporal evolution of dehydrated air masses within the Arctic vortex to be derived and upscaled.
We present validation studies of MLS version 2.2 upper tropospheric and stratospheric ozone profiles using ozonesonde and lidar data as well as climatological data. Ozone measurements from over 60 ...ozonesonde stations worldwide and three lidar stations are compared with coincident MLS data. The MLS ozone stratospheric data between 150 and 3 hPa agree well with ozonesonde measurements, within 8% for the global average. MLS values at 215 hPa are biased high compared to ozonesondes by ∼20% at middle to high latitude, although there is a lot of variability in this altitude region. Comparisons between MLS and ground‐based lidar measurements from Mauna Loa, Hawaii, from the Table Mountain Facility, California, and from the Observatoire de Haute‐Provence, France, give very good agreement, within ∼5%, for the stratospheric values. The comparisons between MLS and the Table Mountain Facility tropospheric ozone lidar show that MLS data are biased high by ∼30% at 215 hPa, consistent with that indicated by the ozonesonde data. We obtain better global average agreement between MLS and ozonesonde partial column values down to 215 hPa, although the average MLS values at low to middle latitudes are higher than the ozonesonde values by up to a few percent. MLS v2.2 ozone data agree better than the MLS v1.5 data with ozonesonde and lidar measurements. MLS tropical data show the wave one longitudinal pattern in the upper troposphere, with similarities to the average distribution from ozonesondes. High upper tropospheric ozone values are also observed by MLS in the tropical Pacific from June to November.
A high-performance Raman lidar operating in the UV portion of the spectrum has been used to acquire, for the first time using a single lidar, simultaneous airborne profiles of the water vapor mixing ...ratio, aerosol backscatter, aerosol extinction, aerosol depolarization and research mode measurements of cloud liquid water, cloud droplet radius, and number density. The Raman Airborne Spectroscopic Lidar (RASL) system was installed in a Beechcraft King Air B200 aircraft and was flown over the mid-Atlantic United States during July August 2007 at altitudes ranging between 5 and 8 km. During these flights, despite suboptimal laser performance and subaperture use of the telescope, all RASL measurement expectations were met, except that of aerosol extinction. Following the Water Vapor Validation Experiment Satellite/Sondes (WAVES_2007) field campaign in the summer of 2007, RASL was installed in a mobile trailer for groundbased use during the Measurements of Humidity and Validation Experiment (MOHAVE-II) field campaign held during October 2007 at the Jet Propulsion Laboratory s Table Mountain Facility in southern California. This ground-based configuration of the lidar hardware is called Atmospheric Lidar for Validation, Interagency Collaboration and Education (ALVICE). During theMOHAVE-II field campaign, during which only nighttime measurements were made, ALVICE demonstrated significant sensitivity to lower-stratospheric water vapor. Numerical simulation and comparisons with a cryogenic frost-point hygrometer are used to demonstrate that a system with the performance characteristics of RASL ALVICE should indeed be able to quantify water vapor well into the lower stratosphere with extended averaging from an elevated location like Table Mountain. The same design considerations that optimize Raman lidar for airborne use on a small research aircraft are, therefore, shown to yield significant dividends in the quantification of lower-stratospheric water vapor. The MOHAVE-II measurements, along with numerical simulation, were used to determine that the likely reason for the suboptimal airborne aerosol extinction performance during theWAVES_2007 campaign was amisaligned interference filter. With full laser power and a properly tuned interference filter,RASL is shown to be capable ofmeasuring themain water vapor and aerosol parameters with temporal resolutions of between 2 and 45 s and spatial resolutions ranging from 30 to 330 m from a flight altitude of 8 km with precision of generally less than 10%, providing performance that is competitive with some airborne Differential Absorption Lidar (DIAL) water vapor and High Spectral Resolution Lidar (HSRL) aerosol instruments. The use of diode-pumped laser technology would improve the performance of an airborne Raman lidar and permit additional instrumentation to be carried on board a small research aircraft. The combined airborne and ground-based measurements presented here demonstrate a level of versatility in Raman lidar that may be impossible to duplicate with any other single lidar technique.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
An algorithm has been developed that retrieves water vapour profiles in the upper troposphere and lower stratosphere from optical depth spectra obtained by the Measurements of Aerosol Extinction in ...the Stratosphere and Troposphere Retrieved by Occultation (MAESTRO) instrument onboard the SCISAT satellite as part of the Atmospheric Chemistry Experiment (ACE) mission. The retrieval relies on ro-vibrational absorption of solar radiation by water vapour in the 926–970
nm range. During the iterative inversion process, the optical depth spectra are simulated at the spectral resolution and sampling frequency of MAESTRO using the correlated-
k approximation. The Chahine inversion updates the water vapour volume mixing ratio (VMR), adjusting all retrieval layers simultaneously, to match the observed differential optical depth due to absorption by water vapour and ozone at each tangent height. This approach accounts for significant line saturation effects. Profiles are typically obtained from ∼22
km down to the cloud tops or to 5
km, with relative precision as small as 3% in the troposphere. In the lower stratosphere, the precision on water vapour VMR is ∼1.3
μmol/mol in an individual retrieval layer (∼1
km thick). The spectral capability of MAESTRO allows for the clear separation of extinction due to water vapour and aerosol, and for the fitting quality to be quantified and used to determine an altitude-dependent convergence criterion for the retrieval. In the middle troposphere, interhemispheric differences in water vapour VMR are driven by oceanic evaporation whereas in the upper troposphere, deep convection dominates and a strong seasonal cycle is observed at high latitudes.
Large areas of synoptic-scale ice PSCs (polar stratospheric clouds) distinguished the Arctic winter 2009/2010 from other years and revealed unprecedented evidence of water redistribution in the ...stratosphere. A unique snapshot of water vapor repartitioning into ice particles was obtained under extremely cold Arctic conditions with temperatures around 183 K. Balloon-borne, aircraft and satellite-based measurements suggest that synoptic-scale ice PSCs and concurrent reductions and enhancements in water vapor are tightly linked with the observed de- and rehydration signatures, respectively. In a companion paper (Part 1), water vapor and aerosol backscatter measurements from the RECONCILE (Reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions) and LAPBIAT-II (Lapland Atmosphere–Biosphere Facility) field campaigns have been analyzed in detail. This paper uses a column version of the Zurich Optical and Microphysical box Model (ZOMM) including newly developed NAT (nitric acid trihydrate) and ice nucleation parameterizations. Particle sedimentation is calculated in order to simulate the vertical redistribution of chemical species such as water and nitric acid. Despite limitations given by wind shear and uncertainties in the initial water vapor profile, the column modeling unequivocally shows that (1) accounting for small-scale temperature fluctuations along the trajectories is essential in order to reach agreement between simulated optical cloud properties and observations, and (2) the use of recently developed heterogeneous ice nucleation parameterizations allows the reproduction of the observed signatures of de- and rehydration. Conversely, the vertical redistribution of water measured cannot be explained in terms of homogeneous nucleation of ice clouds, whose particle radii remain too small to cause significant dehydration.
Radiation balance of the tropical tropopause layer Gettelman, Andrew; Forster, Piers M. de F.; Fujiwara, Masatomo ...
Journal of Geophysical Research - Atmospheres,
16 April 2004, Letnik:
109, Številka:
D7
Journal Article
Recenzirano
Odprti dostop
The radiation balance of the tropical tropopause layer (TTL) is examined using several different radiation codes with standard profiles compiled from observations in the tropics assuming clear sky ...conditions. These codes include detailed radiative transfer models and simplified codes for global climate models. The importance of the various radiatively active gases are examined. Water vapor is the most important contributor to the TTL radiation balance, but carbon dioxide and ozone also play a role. Differences in radiative heating between radiation models are mostly due to treatments of shortwave radiation. Differences between models below the TTL are due to different treatments of water vapor continuum absorption. The level of zero clear sky radiative heating, a level important for understanding the transport of air into the stratosphere, is generally found near 15 km, 125 hPa and 200°K (360 K potential temperature), consistent with previous work. Changes in time and space can modify this level by ±500 m, and individual profiles vary from these averages by ±400 m (1σ). Increases in water vapor in the TTL would tend to increase the altitude of the level at which the net heating is zero, while increases in carbon dioxide or ozone would tend to decrease this level. Clouds in the TTL tend to increase the level due to enhancements in longwave cooling above clouds. The implications for transport are discussed.
The Polar Ozone and Aerosol Measurement (POAM) III solar occultation instrument has been measuring water vapor at high latitudes since April 1998. Retrievals extend from 5 to 50 km, with 5–7% ...precision throughout the stratosphere and a vertical resolution of 1 (3) km in the lower (upper) stratosphere. Estimated systematic errors in the stratosphere are 10–15%. In this paper, we validate the POAM III version 4 stratospheric water vapor using correlative measurements from satellite, airborne, and balloon‐borne platforms. The resulting comparisons show that POAM water vapor is high compared to correlative measurements in the middle to lower stratosphere. The satellite (Halogen Occultation Experiment (HALOE) and Stratospheric Aerosol and Gas Experiment (SAGE) II) comparisons also indicate a sunrise/sunset bias in the POAM data, with sunset (Southern Hemisphere) retrievals larger than sunrise (Northern Hemisphere) retrievals by 5–10%. In the Northern Hemisphere, POAM is approximately 5–10% high compared to all validation data sets between 12 and 35 km. At higher altitudes this difference decreases, such that POAM agrees with HALOE at 40 km and is lower by 10% at 50 km. In the Southern Hemisphere, POAM is 15–25% higher than HALOE below 35 km, with differences decreasing to 10% by 50 km. Similar differences are seen with SAGE II. Despite these systematic differences the POAM water vapor data are self‐consistent and show no long‐term trends in accuracy or precision. Statistical comparisons of the water vapor variability measured by POAM, HALOE, and SAGE II show very good agreement. The POAM data are therefore valid for scientific studies, and the science community is encouraged to use this unique data set.
The Measurements of Humidity in the Atmosphere and Validation Experiment (MOHAVE) 2009 campaign took place on 11–27 October 2009 at the JPL Table Mountain Facility in California (TMF). The main ...objectives of the campaign were to (1) validate the water vapor measurements of several instruments, including, three Raman lidars, two microwave radiometers, two Fourier-Transform spectrometers, and two GPS receivers (column water), (2) cover water vapor measurements from the ground to the mesopause without gaps, and (3) study upper tropospheric humidity variability at timescales varying from a few minutes to several days. A total of 58 radiosondes and 20 Frost-Point hygrometer sondes were launched. Two types of radiosondes were used during the campaign. Non negligible differences in the readings between the two radiosonde types used (Vaisala RS92 and InterMet iMet-1) made a small, but measurable impact on the derivation of water vapor mixing ratio by the Frost-Point hygrometers. As observed in previous campaigns, the RS92 humidity measurements remained within 5% of the Frost-point in the lower and mid-troposphere, but were too dry in the upper troposphere. Over 270 h of water vapor measurements from three Raman lidars (JPL and GSFC) were compared to RS92, CFH, and NOAA-FPH. The JPL lidar profiles reached 20 km when integrated all night, and 15 km when integrated for 1 h. Excellent agreement between this lidar and the frost-point hygrometers was found throughout the measurement range, with only a 3% (0.3 ppmv) mean wet bias for the lidar in the upper troposphere and lower stratosphere (UTLS). The other two lidars provided satisfactory results in the lower and mid-troposphere (2–5% wet bias over the range 3–10 km), but suffered from contamination by fluorescence (wet bias ranging from 5 to 50% between 10 km and 15 km), preventing their use as an independent measurement in the UTLS. The comparison between all available stratospheric sounders allowed to identify only the largest biases, in particular a 10% dry bias of the Water Vapor Millimeter-wave Spectrometer compared to the Aura-Microwave Limb Sounder. No other large, or at least statistically significant, biases could be observed. Total Precipitable Water (TPW) measurements from six different co-located instruments were available. Several retrieval groups provided their own TPW retrievals, resulting in the comparison of 10 different datasets. Agreement within 7% (0.7 mm) was found between all datasets. Such good agreement illustrates the maturity of these measurements and raises confidence levels for their use as an alternate or complementary source of calibration for the Raman lidars. Tropospheric and stratospheric ozone and temperature measurements were also available during the campaign. The water vapor and ozone lidar measurements, together with the advected potential vorticity results from the high-resolution transport model MIMOSA, allowed the identification and study of a deep stratospheric intrusion over TMF. These observations demonstrated the lidar strong potential for future long-term monitoring of water vapor in the UTLS.
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