The Vaisala RS92 radiosonde is the most widely used type of sonde in the current global radiosonde network. One of the largest biases in the RS92 humidity data is its daytime solar radiation dry bias ...(SRDB). An algorithm referred to as NCAR radiation bias correction (NRBC) was developed to correct the SRDB based on a more complicated algorithm developed by the Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN). The NRBC to relative humidity (RH) is a function of the measured RH and temperature, and the temperature solar radiation correction. The latter varies with pressure, season, and time of the day. The RH correction has a mean magnitude of about 2%-4% and 6%-8% in the lower-midtroposphere and upper troposphere, respectively. The NRBC is evaluated against the GRUAN-corrected RS92 data and the ground-based GPS-estimated precipitable water (PW). The corrected RH agrees with the GRUAN data within plus or minus 0.5% on average, with standard deviations of about 1%-2% and 2%-6% in the lower-midtroposphere and upper troposphere, respectively. The NRBC leads to reduced mean biases, and better agreement with the GPS PW and its diurnal cycle. The NRBC has been applied to historical radiosonde data at 65 stations. The radiosonde humidity data, both with and without the NRBC, are homogenized using the method of Dai et al. (2011). The NRBC results in consistently elevated RHs throughout the whole record in the homogenized data. This could have a significant impact on global reanalysis products when they are assimilated into the reanalysis models. However, the NRBC has insignificant effects on the long-term trends as the correction is primarily for mean biases.
Relative humidity (RH) measurements from Vaisala RS92 radiosondes are widely used in research and operational applications, but their accuracy is not well characterized as a function of height, RH, ...and time of day (or solar altitude angle). This study compares RS92 RH measurements to simultaneous water vapor measurements from three reference instruments of known accuracy. Cryogenic frost point hygrometer measurements are used to characterize the RS92 accuracy above the 700‐mbar level, microwave radiometer measurements characterize the RS92 accuracy averaged over essentially the lower troposphere, and the RS92 accuracy at the surface is characterized by a system of 6 RH probes with National Institute of Standards and Technology–traceable calibrations. The three RS92 accuracy assessments are combined to yield a detailed estimate of RS92 accuracy for all RH conditions from the surface to the lowermost stratosphere. An empirical correction is derived to remove the mean bias error, yielding corrected RS92 measurements whose bias uncertainty is independent of height or RH and is estimated to be ±4% of the measured RH value for nighttime soundings and ±5% for daytime soundings, plus an RH offset uncertainty of ±0.5% RH that is significant for dry conditions. The accuracy of an individual RS92 sounding is further characterized by the 1‐σ “random production variability,” estimated to be ±1.5% of the measured RH value. The daytime bias correction must be used with caution, as it is only accurate for clear‐sky or near‐clear conditions owing to the complicated effect of clouds on the solar radiation error.
Radiosonde observations (RAOBs) have provided the only long-term global in situ temperature measurements in the troposphere and lower stratosphere since 1958. In this study, we use consistently ...reprocessed Global Positioning System (GPS) radio occultation (RO) temperature data derived from the COSMIC and Metop-A/GRAS missions from 2006 to 2014 to characterize the inter-seasonal and interannual variability of temperature biases in the upper troposphere and lower stratosphere for different radiosonde sensor types. The results show that the temperature biases for different sensor types are mainly due to (i) uncorrected solar-zenith-angle-dependent errors and (ii) change of radiation correction. The mean radiosonde–RO global daytime temperature difference in the layer from 200 to 20 hPa for Vaisala RS92 is equal to 0.20 K. The corresponding difference is equal to −0.06 K for Sippican, 0.71 K for VIZ-B2, 0.66 K for Russian AVK-MRZ, and 0.18 K for Shanghai. The global daytime trend of differences for Vaisala RS92 and RO temperature at 50 hPa is equal to 0.07 K/5 yr. Although there still exist uncertainties for Vaisala RS92 temperature measurement over different geographical locations, the global trend of temperature differences between Vaisala RS92 and RO from June 2006 to April 2014 is within ±0.09 K/5 yr. Compared with Vaisala RS80, Vaisala RS90, and sondes from other manufacturers, the Vaisala RS92 seems to provide the most accurate RAOB temperature measurements, and these can potentially be used to construct long-term temperature climate data records (CDRs). Results from this study also demonstrate the feasibility of using RO data to correct RAOB temperature biases for different sensor types.
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.
Low ozone and high water vapour mixing ratios are common features in the Asian summer monsoon (ASM) anticyclone; however, low ozone and low water vapour values were observed near the tropopause over ...Kunming, China, within the ASM using balloon-borne measurements performed during the SWOP (sounding water vapour, ozone, and particle) campaign in August 2009 and 2015.
Here, we investigate low ozone and water vapour signatures in the upper troposphere and lower stratosphere (UTLS) using FengYun-2D, FengYun-2G, and Aura Microwave Limb Sounder (MLS) satellite measurements and backward trajectory calculations.
Trajectories with kinematic and diabatic vertical velocities were calculated using the Chemical Lagrangian Model of the Stratosphere (CLaMS) trajectory module driven by both ERA-Interim and ERA5 reanalysis data. All trajectory calculations show that air parcels with low ozone and low water vapour values in the UTLS over Kunming measured by balloon-borne instruments originate from the western Pacific boundary layer.
Deep convection associated with tropical cyclones over the western Pacific transports ozone-poor air from the marine boundary layer to the cold tropopause region.
Subsequently, these air parcels are mixed into the strong easterlies on the southern side of the Asian summer monsoon anticyclone.
Air parcels are dehydrated when passing the lowest temperature region (< 190 K) at the convective outflow of tropical cyclones.
However, trajectory calculations show different vertical transport via deep convection depending on the employed reanalysis data (ERA-Interim, ERA5) and vertical velocities (diabatic, kinematic).
Both the kinematic and the diabatic trajectory calculations using ERA5 data show much faster and stronger vertical transport than ERA-Interim primarily because of ERA5's better spatial and temporal resolution, which likely resolves convective events more accurately.
Our findings show that the interplay between the ASM anticyclone and tropical cyclones has a significant impact on the chemical composition of the UTLS during summer.
The Asian summer monsoon (ASM) anticyclone circulation system is recognized to be a significant transport pathway for water vapor and pollutants to enter the stratosphere. The observational evidence, ...however, is largely based on satellite retrievals. We report the first coincident in situ measurements of water vapor and ozone within the ASM anticyclone. The combined water vapor and ozonesondes were launched from Kunming, China in August 2009 and Lhasa, China in August 2010. In total, 11 and 12 sondes were launched in Kunming and Lhasa, respectively. We present the key characteristics of these measurements, and provide a comparison to similar measurements from an equatorial tropical location, during the Tropical Composition, Cloud and Climate Coupling (TC4) campaign in July and August of 2007. Results show that the ASM anticyclone region has higher water vapor and lower ozone concentrations in the upper troposphere and lower stratosphere than the TC4 observations. The results also show that the cold point tropopause in the ASM region has a higher average height and potential temperature. The in situ observations therefore support the satellite‐based conclusion that the ASM is an effective transport pathway for water vapor to enter stratosphere.
Key Points
First in situ measurements of water vapor and ozone within the ASM anticyclone
ASM anticyclone has higher water vapor and lower ozone in the UTLS
ASM region has a higher cold point tropopause level
The Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) field campaign provides accurate data for aerosol characterization and trace gas profiles, and establishes ...knowledge of the relationships between aerosols and water. The dropsonde dataset provides an in situ characterization of the vertical thermodynamic structure of the atmosphere during 165 research flights by NASA Langley's King Air research aircraft between February 2020 and June 2022 and four test flights between December 2019 and November 2021. The research flights covered the western North Atlantic region, off the coast of the Eastern United States and around Bermuda and covered all seasons. The dropsonde profiles provide observations of temperature, pressure, relative humidity, and horizontal and vertical winds between the surface and about 9 km. 801 dropsondes were released, of which 796 were processed and 788 provide complete profiles of all parameters between the flight level and the surface with normal parachute performance. Here, we describe the dataset, the processing of the measurements, general statistics, and applications of this rich dataset.
Balloon-borne measurements of ozone in Lhasa (29.66∘ N,
91.14∘ E; 3650 m above sea level) in August 2013 are investigated
using backward trajectory calculations performed with the Chemical Lagrangian
...Model of the Stratosphere (CLaMS). Measurements show three time periods
characterized by high ozone mixing ratios (OMRs) in the troposphere on 8, 11,
and 18–20 August 2013 during the Asian summer monsoon (ASM) season. Here, we
verified two different sources for the enhanced ozone values in the
troposphere. First, transport of polluted air from the boundary layer, and
second downward transport from the stratosphere by stratospheric intrusions.
Air pollution from South Asia through convective and long-range transport
plays a key role in enhancing middle tropospheric OMRs up to 90 % on
8 August and up to 125 % on 11 August 2013 compared to monthly mean ozone
of August 2013. Stratospheric air intruded from the northern high-latitudes
to the southeastern flank of the ASM anticyclone to the troposphere and is
identified as the source of enhanced ozone according to backward trajectory
calculation and satellite measurements by the Ozone Monitoring Instrument
(OMI) and the Atmospheric Infrared Sounder (AIRS). Air parcels with high
ozone moved from the high-latitude lower stratosphere to the middle and upper
troposphere. These air parcels are then transported to Lhasa over long
distances and enhanced upper and middle tropospheric ozone over Lhasa during
18–20 August 2013. Our findings demonstrate that the strong variability of
ozone within the ASM anticyclone in the free troposphere is caused by
transport from very different regions of the atmosphere.
Large volcanic eruptions, although rare events, can influence the chemistry and the dynamics of the stratosphere for several years after the eruption. Here we show that the eruption of the submarine ...volcano Hunga Tonga-Hunga Ha’apai on 15 January 2022 injected at least 50 teragrams of water vapor directly into the stratosphere. This event raised the amount of water vapor in the developing stratospheric plume by several orders of magnitude and possibly increased the amount of global stratospheric water vapor by more than 5%. This extraordinary eruption may have initiated an atmospheric response different from that of previous well-studied large volcanic eruptions.
Up in the air
The eruption of the submarine volcano Hunga Tonga-Hunga Ha’apai in January of 2022 was so violent that its plume penetrated into the stratosphere. Vömel
et al
. studied in situ measurements by radiosondes (weather balloons), which showed that the event injected at least 50 teragrams of water vapor into the stratosphere. Because the volcano was underwater, the amount of water vapor in the developing stratospheric plume was high, and, unlike other large eruptions, it may have increased the amount of global stratospheric water vapor by more than 5%. —HJS
The eruption of the submarine volcano Hunga Tonga-Hunga Ha’apai added an extraordinary volume of water into the stratosphere.
A large-scale comparison of water-vapour vertical-sounding instruments took place over central Europe on 17 October 2008, during a rather homogeneous deep stratospheric intrusion event (LUAMI, ...Lindenberg Upper-Air Methods Intercomparison). The measurements were carried out at four observational sites: Payerne (Switzerland), Bilthoven (the Netherlands), Lindenberg (north-eastern Germany), and the Zugspitze mountain (Garmisch-Partenkichen, German Alps), and by an airborne water-vapour lidar system creating a transect of humidity profiles between all four stations. A high data quality was verified that strongly underlines the scientific findings. The intrusion layer was very dry with a minimum mixing ratios of 0 to 35 ppm on its lower west side, but did not drop below 120 ppm on the higher-lying east side (Lindenberg). The dryness hardens the findings of a preceding study (“Part 1”, Trickl et al., 2014) that, e.g., 73 % of deep intrusions reaching the German Alps and travelling 6 days or less exhibit minimum mixing ratios of 50 ppm and less. These low values reflect values found in the lowermost stratosphere and indicate very slow mixing with tropospheric air during the downward transport to the lower troposphere. The peak ozone values were around 70 ppb, confirming the idea that intrusion layers depart from the lowermost edge of the stratosphere. The data suggest an increase of ozone from the lower to the higher edge of the intrusion layer. This behaviour is also confirmed by stratospheric aerosol caught in the layer. Both observations are in agreement with the idea that sections of the vertical distributions of these constituents in the source region were transferred to central Europe without major change. LAGRANTO trajectory calculations demonstrated a rather shallow outflow from the stratosphere just above the dynamical tropopause, for the first time confirming the conclusions in “Part 1” from the Zugspitze CO observations. The trajectories qualitatively explain the temporal evolution of the intrusion layers above the four stations participating in the campaign.
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