Holger Vömel

Southern Hemisphere Additional Ozonesondes (SHADOZ) 1998–2000 tropical ozone climatology 1. Comparison with Total Ozone Mapping Spectrometer (TOMS) and ground-based measurements

[1]xa0A 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; Reunion Island; Watukosek, Java; Fiji; Tahiti; American Samoa; San Cristobal, 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.

The Stratospheric Water and Ozone Satellite Homogenized (SWOOSH) database:a long-term database for climate studies

In this paper, we describe the construction of the Stratospheric Water and Ozone Satellite Homogenized (SWOOSH) database, which includes vertically resolved ozone and water vapor data from a subset of the limb profiling satellite instruments operating since the 1980s. The primary SWOOSH products are zonal-mean monthly-mean time series of water vapor and ozone mixing ratio on pressure levels (12 levels per decade from 316 to 1 hPa). The SWOOSH pressure level products are provided on several independent zonal-mean grids (2.5, 5, and 10°), and additional products include two coarse 3-D griddings (30° long × 10° lat, 20° × 5°) as well as a zonal-mean isentropic product. SWOOSH includes both individual satellite source data as well as a merged data product. A key aspect of the merged product is that the source records are homogenized to account for inter-satellite biases and to minimize artificial jumps in the record. We describe the SWOOSH homogenization process, which involves adjusting the satellite data records to a reference satellite using coincident observations during time periods of instrument overlap. The reference satellite is chosen based on the best agreement with independent balloon-based sounding measurements, with the goal of producing a long-term data record that is both homogeneous (i.e., with minimal artificial jumps in time) and accurate (i.e., unbiased). This paper details the choice of reference measurements, homogenization, and gridding process involved in the construction of the combined SWOOSH product and also presents the ancillary information stored in SWOOSH that can be used in future studies of water vapor and ozone variability. Furthermore, a discussion of uncertainties in the combined SWOOSH record is presented, and examples of the SWOOSH record are provided to illustrate its use for studies of ozone and water vapor variability on interannual to decadal timescales. The version 2.5 SWOOSH data are publicly available at doi:10.7289/V5TD9VBX.

Reference Upper-Air Observations for Climate: From Concept to Reality

AbstractThe three main objectives of the Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN) are to provide long-term high-quality climate records of vertical profiles of selected essential climate variables (ECVs), to constrain and calibrate data from more spatially comprehensive global networks, and to provide measurements for process studies that permit an in-depth understanding of the properties of the atmospheric column. In the five years since the first GRUAN implementation and coordination meeting and the printing of an article (Seidel et al.) in this publication, GRUAN has matured to become a functioning network that provides reference-quality observations to a community of users.This article describes the achievements within GRUAN over the past five years toward making reference-quality observations of upper-air ECVs. Milestones in the evolution of GRUAN are emphasized, including development of rigorous criteria for site certification and assessment, the formal certificatio...

High supersaturation inside cirrus in well-developed tropical tropopause layer over Indonesia

[1]xa0The relationship between relative humidity and cirrus clouds in the tropical tropopause layer (TTL) is investigated using balloon-borne cryogenic frostpoint hygrometers (CFH) and quasi-collocated measurements of space-borne Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) over Biak (1.17°S, 136.06°E) and Kototabang (0.20°S, 100.32°E) both in Indonesia in Januaries 2007 and 2008. At Kototabang, thin layers of high supersaturation, up to ∼160% in relative humidity with respect to ice (RHi), are often observed co-existing with cirrus clouds at altitudes of ∼15–18xa0km. At Biak, RHi inside cirrus is around 100% or less without large supersaturation layers, and most clouds are limited to altitudes below 16xa0km. We found that the presence and the degree of supersaturation may strongly depend on the phases of large-scale disturbances such as the MJO rather than geographical difference.

Recent divergences in stratospheric water vapor measurements by frost pointhygrometers and the Aura Microwave Limb Sounder

Balloon-borne frost point hygrometers (FPs) and the Aura Microwave Limb Sounder (MLS) provide high-quality vertical profile measurements of water vapor in the upper troposphere and lower stratosphere (UTLS). A previous comparison of stratospheric water vapor measurements by FPs and MLS over three sites - Boulder, Colorado (40.0° N); Hilo, Hawaii (19.7° N); and Lauder, New Zealand (45.0° S) - from August 2004 through December 2012 not only demonstrated agreement better than 1% between 68 and 26 hPa but also exposed statistically significant biases of 2 to 10% at 83 and 100 hPa (Hurst et al., 2014). A simple linear regression analysis of the FP-MLS differences revealed no significant long-term drifts between the two instruments. Here we extend the drift comparison to mid-2015 and add two FP sites - Lindenberg, Germany (52.2° N), and San José, Costa Rica (10.0° N) - that employ FPs of different manufacture and calibration for their water vapor soundings. The extended comparison period reveals that stratospheric FP and MLS measurements over four of the five sites have diverged at rates of 0.03 to 0.07 ppmv year−1 (0.6 to 1.5% year−1) from ~2010 to mid-2015. These rates are similar in magnitude to the 30-year (1980–2010) average growth rate of stratospheric water vapor (~ 1% year−1) measured by FPs over Boulder (Hurst et al., 2011). By mid-2015, the FP–MLS differences at some sites were large enough to exceed the combined accuracy estimates of the FP and MLS measurements.

First Reprocessing of Southern Hemisphere Additional Ozonesondes (SHADOZ) Ozone Profiles (1998–2016): 2. Comparisons With Satellites and Ground‐Based Instruments

Abstract The Southern Hemisphere ADditional OZonesonde (SHADOZ) network was assembled to validate a new generation of ozone-monitoring satellites and to better characterize the vertical structure of tropical ozone in the troposphere and stratosphere. Beginning with nine stations in 1998, more than 7,000 ozone and P-T-U profiles are available from 14 SHADOZ sites that have operated continuously for at least a decade. We analyze ozone profiles from the recently reprocessed SHADOZ data set that is based on adjustments for inconsistencies caused by varying ozonesonde instruments and operating techniques. First, sonde-derived total ozone column amounts are compared to the overpasses from the Earth Probe/Total Ozone Mapping Spectrometer, Ozone Monitoring Instrument, and Ozone Mapping and Profiler Suite satellites that cover 1998-2016. Second, characteristics of the stratospheric and tropospheric columns are examined along with ozone structure in the tropical tropopause layer (TTL). We find that (1) relative to our earlier evaluations of SHADOZ data, in 2003, 2007, and 2012, sonde-satellite total ozone column offsets at 12 stations are 2% or less, a significant improvement; (2) as in prior studies, the 10 tropical SHADOZ stations, defined as within ±19° latitude, display statistically uniform stratospheric column ozone, 229 ± 3.9 DU (Dobson units), and a tropospheric zonal wave-one pattern with a 14 DU mean amplitude; (3) the TTL ozone column, which is also zonally uniform, masks complex vertical structure, and this argues against using satellites for lower stratospheric ozone trends; and (4) reprocessing has led to more uniform stratospheric column amounts across sites and reduced bias in stratospheric profiles. As a consequence, the uncertainty in total column ozone now averages 5%.

Advancements, measurement uncertainties, and recent comparisons of the NOAAfrost point hygrometer

The NOAA frost point hygrometer (FPH) is a balloon-borne instrument flown monthly at three sites to measure water vapor profiles up to 28 km. The FPH record from Boulder, Colorado, is the longest continuous stratospheric water vapor record. The instrument has an uncertainty in the stratosphere that is < 6 % and up to 12 % in the troposphere. A digital microcontroller version of the instrument improved upon the older versions in 2008 with sunlight filtering, better frost control, and resistance to radio frequency interference (RFI). A new thermistor calibration technique was implemented in 2014, decreasing the uncertainty in the thermistor calibration fit to less than 0.01 °C over the full range of frost – or dew point temperatures (−93 to +20 °C) measured during a profile. Results from multiple water vapor intercomparisons are presented, including the excellent agreement between the NOAA FPH and the direct tunable diode laser absorption spectrometer (dTDLAS) MC-PicT-1.4 during AquaVIT-2 chamber experiments over 6 days that provides confidence in the accuracy of the FPH measurements. Dual instrument flights with two FPHs or an FPH and a cryogenic frost point hygrometer (CFH) also show good agreement when launched on the same balloon. The results from these comparisons demonstrate the high level of accuracy of the NOAA FPH.

Validation of Aura Microwave Limb Sounder water vapor and ozone profiles over the Tibetan Plateau and its adjacent region during boreal summer

We present validation studies of MLS V2.2 and V3.3 water vapor (WV) and ozone profiles over the Tibetan Plateau (Naqu and Lhasa) and its adjacent region (Tengchong) respectively by using the balloon-borne Cryogenic Frost point Hygrometer and Electrochemical Concentration Cell ozonesonde. Coincident in situ measurements were selected to compare the MLS V2.2 and V3.3 WV and ozone profiles for understanding the applicability of the two version MLS products over the region. MLS V2.2 and V3.3 WV profiles respectively show their differences within −2.2±15.7% (n=74) and 0.3±14.9% (n=75) in the stratosphere at and above 82.5 hPa. Accordingly, at 100 hPa, the altitude approaching the tropopuase height, differences are within 9.8±46.0% (n=18) and 23.0±45.8% (n=17), and they are within 21.5±90.6% (n=104) and 6.0±83.4% (n=99) in upper troposphere. The differences of MLS ozone are within −11.7±16.3% (n=135, V2.2) and 15.6±24.2% (n=305, V3.3) at and above 82.5 hPa. At 100 hPa, they are within −3.5±54.4% (n=27) and −8.7±41.6% (n=38), and within 18.0±79.1% (n=47) and 34.2±76.6% (n=160) in the upper troposphere. The relative difference of MLS WV and ozone profile has significant oscillation and scatter at upper troposphere and lower stratosphere partly due to the stronger gradients of WV and ozone concentrations here as well the linear interpolation of sonde data for the intercomparison. At and below 70 hPa, the relative differences of MLS ozone are significantly larger over Lhasa during the Tibetan Plateau “ozone valley” season, which is also the Asian Summer Monsoon period. The MLS ozone differences over the three sites are similar in their vertical distributions during that period. A simple linear correlation analysis between MLS and sonde profiles indicates that the sensitivity of MLS profile products is related to concentrations at each pressure level. The MLS V3.3 product sensitivity is slightly improved for WV at and above 82.5 hPa, whereas it is not obvious for ozone. The possible factors contributing to the differences of the MLS profile products of WV and ozone are discussed.

Sources of seasonal variability in tropical upper troposphere and lower stratosphere water vapor and ozone: Inferences from the Ticosonde data set at Costa Rica

We present an analysis of joint balloonsonde profiles of water vapor and ozone made at Costa Rica from 2005 to 2011 using compositing techniques, tracer-tracer diagrams, and back trajectory methods. Our analysis reveals important seasonal differences in structure in the upper troposphere and lower stratosphere. Water vapor amounts in boreal winter at Costa Rica are much lower than expected from local ice saturation temperatures. The boreal summer data show both higher average water vapor amounts and a much higher level of variability than the winter data. To understand this seasonal contrast, we consider three sources of tracer variability: wave-induced vertical motion across strong vertical gradients (“wave variability”), differences in source air masses resulting from horizontal transport (“source variability”), and changes induced along parcel paths due to physical processes (“path variability”). The winter and summer seasons show different mixes of these three sources of variability with more air originating in the tropical western Pacific during winter.

First Reprocessing of Southern Hemisphere ADditional OZonesondes Profile Records: 3. Uncertainty in Ozone Profile and Total Column

Reprocessed ozonesonde data from eight SHADOZ (Southern Hemisphere ADditional OZonesondes) sites have been used to derive the first analysis of uncertainty estimates for both profile and total column ozone (TCO). The ozone uncertainty is a composite of the uncertainties of the individual terms in the ozone partial pressure (PO3) equation, those being the ozone sensor current, background current, internal pump temperature, pump efficiency factors, conversion efficiency, and flow-rate. Overall, PO3 uncertainties (ΔPO3) are within 15% and peak around the tropopause (15±3km) where ozone is a minimum and ΔPO3 approaches the measured signal. The uncertainty in the background and sensor currents dominate the overall ΔPO3 in the troposphere including the tropopause region, while the uncertainties in the conversion efficiency and flow-rate dominate in the stratosphere. Seasonally, ΔPO3 is generally a maximum in the March-May, with the exception of SHADOZ sites in Asia, for which the highest ΔPO3 occurs in September-February. As a first approach, we calculate sonde TCO uncertainty (ΔTCO) by integrating the profile ΔPO3 and adding the ozone residual uncertainty, derived from the McPeters and Labow [2012] 1-σ ozone mixing ratios. Overall, ΔTCO are within ±15 DU, representing ~5-6% of the TCO. TOMS and OMI satellite overpasses are generally within the sonde ΔTCO. However, there is a discontinuity between TOMS v8.6 (1998-2004/09) and OMI (2004/10-2016) TCO on the order of 10DU that accounts for the significant 16DU overall difference observed between sonde and TOMS. By comparison, the sonde-OMI absolute difference for the eight stations is only ~4DU.