Search

A total of 99 dual soundings with Meisei iMS-100 radiosonde and Vaisala RS92 radiosondes were carried out at the Aerological Observatory of the Japan Meteorological Agency, known as Tateno (36.06∘ N, 140.13∘ E, 25.2 m; the World Meteorological Organization, WMO, station number 47646), from September 2017 to January 2020. Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN) data products (GDPs) from both sets of radiosonde data for 59 flights were subsequently created using a documented processing programme along with the provision of optimal estimates for measurement uncertainty. Differences in radiosonde performance were then quantified using these GDPs. For daytime observations, the iMS-100 temperature is around 0.5 K cooler than RS92-GDP in the stratosphere, with significant differences in the upper troposphere and lower stratosphere in consideration of combined uncertainties. For nighttime observations, the difference is around −0.1 K, and data are mostly in agreement. For relative humidity (RH), iMS-100 is around 1 % RH–2 % RH higher in the troposphere and 1 % RH smaller in the stratosphere than RS92, but both GDPs are in agreement for most of the profile. The mean pressure difference is ≤0.1 hPa, the wind speed difference is from −0.04 to +0.14 m s−1, the wind direction difference is ≤6.4∘, and the root mean square vector difference (RMSVD) for wind is ≤1.04 m s−1.

Large-and-Sparse-particle Clouds (LSC), characterized by large particle size (radius > 50 μm) and small number concentration (

Using COSMIC GPS Radio Occultation (RO) observations from January 2007 to December 2016, we retrieved temperature profiles with the height resolution of about 0.1 km in the upper troposphere and lower stratosphere (UTLS). We investigated the distribution of static stability (N2) and the zonal structure of the tropopause inversion layer (TIL) in the tropics, where a large change in the temperature gradient occurs associated with sharp variations in N2. We show the variations in the mean N2 profiles in coordinates relative to the cold-point tropopause (CPT). A very thin ( km) layer is found with average maximum N2 in the range of 11.0–12.0×10-4 s−2. The mean and standard deviation of TIL sharpness, defined as the difference between the maximum N2 (max⁡N2) and minimum N2 (min⁡N2) within ±1 km of the CPT, is (10.5±3.7)×10-4 s−2. The max⁡N2 is typically located within 0.5 km above CPT. We focused on the variation in TIL sharpness in two longitude regions, 90–150∘ E (Maritime Continent; MC) and 170–230∘ E (Pacific Ocean; PO), with different land–sea distribution. Seasonal variations in TIL sharpness and thickness were related to the deep convective activity represented by low outgoing longwave radiation (OLR) during the Australian and Asian monsoons. The deviation from the mean sharpness (sharpness anomaly) was out of phase with the OLR anomaly in both the MC and PO. The correlation between the sharpness anomaly over the MC and PO and the sea surface temperature (SST) Niño 3.4 index was −0.66 and +0.88, respectively. During La Niña (SST Niño 3.4 <-0.5 K) in the MC and El Niño (SST Niño 3.4 >+0.5 K) in the PO, warmer SSTs in the MC and PO produce more active deep convection that tends to force the air upward to the tropopause layer and increase the temperature gradient there. The intraseasonal variation in sharpness anomaly during slow and fast episodes of the Madden–Julian Oscillation (MJO) demonstrates that eastward propagation of the positive sharpness anomaly is associated with organized deep convection. Deep convection during MJO will tend to decrease N2 below CPT and increase N2 above CPT, thus enlarging the TIL sharpness. Convective activity in the tropics is a major control on variations in tropopause sharpness at intraseasonal to interannual timescales.

This report outlines the structure of and summarizes the recommendations made at the 5th International Conference on Reanalysis (ICR5), attended by 259 participants from 37 countries, in Rome (Italy), on 13-17 November 2017. It first summarizes the conference structure. Then, the key recommendations of ICR5 are given for the five main conference topics: production; observations (data rescue and preparation); data assimilation methods; quality assurance of reanalysis; and applications in science, services, and policymaking. Lastly, five high-level recommendations are proposed to managing agencies on how best to advance the field of reanalyses, which serves tens of thousands of users, via enhanced research, development, and operations.

Electrochemical concentration cell ozonesonde measurements are an important source of highly resolved vertical profiles of ozone with long-term data records for deriving ozone trends, model development, satellite validation, and air quality studies. Ozonesonde stations employ a range of operational and data processing procedures, metadata reporting, and instrument changes that have resulted in inhomogeneities within individual station data records. A major milestone is the first reprocessing of seven Southern Hemisphere ADditional OZonesondes (SHADOZ) station ozonesonde records to account for errors and biases in operating/processing procedures. Ascension Island, Hanoi, Irene, Kuala Lumpur, La Reunion, Natal, and Watukosek station records all show an overall increase in ozone after reprocessing. Watukosek shows the largest increase of 9.0 plus or minus 2.1 Dobson Units (DU) in total column ozone; Irene and Hanoi show a 5.5 plus or minus 2.5 DU increase, while remaining sites show statistically insignificant enhancements. Negligible to modest ozone enhancements are observed after reprocessing in the troposphere (up to 8%) and stratosphere (up to 6%), except at La Reunion for which the application of background currents reduces tropospheric ozone (2.1 plus or minus1.3 DU). Inhomogeneities due to ozonesonde/solution-type changes at Ascension, Natal, and La Reunion are resolved with the application of transfer functions. Comparisons with EP-TOMS, Aura's Ozone Monitoring Instrument and Microwave Limb Sounder (MLS) satellite ozone overpasses show an overall improvement in agreement after reprocessing. Most reprocessed data sets show a significant reduction in biases with MLS at the ozone maximum region (50-10 hPa). Changes in radiosonde/ozonesonde system and nonstandard solution types can account for remaining discrepancies observed at several sites when compared to satellites.

Increasing interest in climate engineering in recent years has led to calls by the international research community for international research collaboration as well as global public engagement. But making such collaboration a reality is challenging. Here, we report the summary of a 2016 workshop on the significance and challenges of international collaboration on climate engineering research with a focus on the Asia-Pacific region. Because of the region’s interest in benefits and risks of climate engineering, there is a potential synergy between impact research on anthropogenic global warming and that on solar radiation management. Local researchers in the region can help make progress toward better understanding of impacts of solar radiation management. These activities can be guided by an ad hoc Asia-Pacific working group on climate engineering, a voluntary expert network. The working group can foster regional conversations in a sustained manner while contributing to capacity building. An important theme in the regional conversation is to develop effective practices of dialogues in light of local backgrounds such as cultural traditions and past experiences of large-scale technology development. Our recommendation merely portrays one of several possible ways forward, and it is our hope to stimulate the debate in the region.

Atmospheric balloon soundings have been made since the end of the 19th century. In recent decades, specific upper-air radiosonde measurements have become important for climate monitoring and atmosp...

A total of 87 dual flights of Meisei RS-11G radiosondes and Vaisala RS92-SGP radiosondes were carried out at the Aerological Observatory of the Japan Meteorological Agency (36.06∘ N, 140.13∘ E, 25.2 m) from April 2015 to June 2017. Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN) data products from both sets of radiosonde data for 52 flights were subsequently created using a documented processing program along with the provision of optimal estimates for measurement uncertainty. Differences in the performance of the radiosondes were then quantified using the GRUAN data products. The temperature measurements of RS-11G were, on average, 0.4 K lower than those of RS92-SGP in the stratosphere for daytime observations. The relative humidity measurements of RS-11G were, on average, 2 % RH (relative humidity) lower than those of RS92-SGP under 90 % RH–100 % RH conditions, while RS-11G gave on average 5 % RH higher values than RS92-SGP under ≤50 % RH conditions. The results from a dual flight of RS-11G and a cryogenic frost point hygrometer (CFH) also showed that RS-11G gave 1 % RH–10 % RH higher values than the CFH in the troposphere. Differences between the RS-11G and RS92-SGP temperature and relative humidity measurements, based on combined uncertainties, were also investigated to clarify major influences behind the differences. It was found that temperature differences in the stratosphere during daytime observation were within the range of uncertainty (k=2), and that sensor orientation is the major source of uncertainty in the RS92-SGP temperature measurement, while sensor albedo is the major source of uncertainty for RS-11G. The relative humidity difference in the troposphere was larger than the uncertainty (k=2) after the radiosondes had passed through the cloud layer, and the temperature–humidity dependence correction was the major source of uncertainty in RS-11G relative humidity measurement. Uncertainties for all soundings were also statistically investigated. Most nighttime temperature measurements for pressures of >10 hPa were in agreement, while relative humidity in the middle troposphere exhibited significant differences. Around half of all daytime temperature measurements at pressures of ≤150 hPa and relative humidity measurements around the 500 hPa level were not in agreement.

Interest in climate engineering research has grown rapidly owing to the slow progress of international climate negotiations. As some scientists are proposing to expand research and conduct field tests, there is an emerging debate about whether and how it should proceed. It is widely accepted both by the supporters and critics that public engagement from the early stage of research is necessary. Nonetheless, most, if not all, of existing research projects of climate engineering were designed predominantly by experts. To produce socially relevant knowledge, and hence, pursue transdisciplinary research that integrates interdisciplinary research and public engagement, it is desirable for scientists to decide together with the public on what kind of research should be done. In this paper, we both as Japanese scientists and stakeholders collaboratively identify 40 socially relevant research questions on climate engineering with a particular emphasis on stratospheric aerosol injection, using a method designed to encourage science–policy collaboration. While we acknowledge some methodological problems and the difficulty in obtaining active participation from stakeholders, the list of identified questions covers broad interdisciplinary perspectives and diverse interests, and may provide an important foundation for future transdisciplinary research on climate engineering. Given the dynamic nature of climate change and policy responses, research agendas should be periodically and iteratively reviewed and updated through transdisciplinary processes.

This paper reports on a project to compare the representation of the monthly-mean zonal wind in the equatorial stratosphere among major global atmospheric reanalysis datasets. The degree of disagreement among the reanalyses is characterized by the standard deviation (SD) of the monthly-mean zonal wind and this depends on latitude, longitude, height and the phase of the quasi-biennial oscillation (QBO). At each height the SD displays a prominent equatorial maximum, indicating the particularly challenging nature of the reanalysis problem in the low-latitude stratosphere. At 50–70 hPa the geographical distributions of SD are closely related to the density of radiosonde observations. The largest SD values are over the eastern Pacific, where few in situ observations are available. At 10–20 hPa the spread among the reanalyses and differences with in situ observations both depend significantly on the QBO phase. Notably the easterly-to-westerly phase transitions in all the reanalyses except MERRA are delayed relative to those directly observed at Singapore. In addition, the timing of the easterly-to-westerly phase transitions displays considerable variability among the different reanalyses and this spread is much larger than for the timing of the westerly-to-easterly phase changes. The eddy component in the monthly mean zonal wind near the equator is dominated by zonal wavenumber 1 and 2 quasi-stationary planetary waves propagating from mid-latitudes in the westerly phase of the QBO. There generally is considerable disagreement among the reanalyses in the details of the quasi-stationary waves near the equator. At each level, there is a tendency for the agreement to be best near the longitude of Singapore, suggesting that the Singapore observations act as a strong constraint on all the reanalyses. Our measures of the quality of the reanalysis clearly show systematic improvement over the period considered (1979–2012). The SD among the reanalysis declines significantly over the record, although the geographical pattern of SD remains nearly constant.

The 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 7000 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 dataset 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 EP/TOMS, OMI and OMPS 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 ten tropical SHADOZ stations, defined as within +19 degrees latitude, display statistically uniform stratospheric column ozone, 229 + 3.9 DU, 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; this argues against using satellites for lower stratospheric ozone trends. (4) Reprocessing has led to more uniform stratospheric column amounts across sites and reduced bias in stratospheric profiles. As a consequence the variability in total column ozone now averages 5%.

The impact of the recent minor volcanic eruptions during 2001–2010 in the temperature of the upper troposphere and lower stratosphere (UTLS) is investigated using data from the Global Positioning System Radio Occultation (GPS RO), three radiosonde compilations and two reanalyses (ERA-Interim and MERRA). The volcanic signals are identified in the residual temperature time series after removal of the linear trend, the quasi-biennial oscillation and El Nino Southern Oscillation components. Eight minor volcanic eruptions (six from the tropics and two from midlatitude) over the last decade (2001–2010) are analyzed in this study. We found significant volcanic signals in the UTLS temperature only in association with the tropical Soufriere Hills and Tavurvur eruptions (in May 2006 and in October 2006, respectively). Other four tropical eruptions had very small aerosol perturbations and did not show any significant UTLS temperature change. Out of the two midlatitude eruptions, Sarychev peak had similar stratospheric aerosol perturbations as Soufriere Hills and Tavurvur eruptions, but did not show any significant UTLS temperature change. The volcanic signals in the UTLS temperature from the tropical Soufriere Hills and Tavurvur eruptions were observed for the period of 7 months after August 2006. A warming of 0.5–0.8 K in the tropical 16–18.5 km (100–70 hPa) layer was observed in association with these two tropical eruptions.

A multiple linear regression analysis of nine different reanalysis datasets has been performed to test the robustness of variability associated with volcanic eruptions, the El Nino Southern Oscillation, the Quasi-Biennial Oscillation and with a specific focus on the 11-year solar cycle. The analysis covers both the stratosphere and troposphere and extends over the period 1979–2009. The characteristic signals of all four sources of variability are remarkably consistent between the datasets and confirm the responses seen in previous analyses. In general, the solar signatures reported are primarily due to the assimilation of observations, rather than the underlying forecast model used in the reanalysis system. Analysis of the 11-year solar response in the lower stratosphere confirms the existence of the equatorial temperature maximum, although there is less consistency in the upper stratosphere, probably reflecting the reduced level of assimilated data there. The solar modulation of the polar jet oscillation is also evident, but only significant during February. In the troposphere, vertically banded anomalies in zonal mean zonal winds are seen in all the reanalyses, with easterly anomalies at 30°N and 30°S suggesting a weaker and possibly broader Hadley circulation under solar maximum conditions. This structure is present in the annual signal and is particularly evident in NH wintertime. As well as the ‘top-down’ solar contribution to Northern Annular Mode variability, we show the potential contribution from the surface conditions allowing for a ‘bottom-up’ pathway. Finally, the reanalyses are compared with both observed global-mean temperatures from the Stratospheric Sounding Unit (SSU) and from the latest general circulation models from CMIP-5. The SSU samples the stratosphere over three different altitudes, and the 11-year solar cycle fingerprint is identified in these observations using detection and attribution techniques.

The climate research community uses atmospheric reanalysis data sets to understand a wide range of processes and variability in the atmosphere, yet different reanalyses may give very different results for the same diagnostics. The Stratosphere–troposphere Processes And their Role in Climate (SPARC) Reanalysis Intercomparison Project (S-RIP) is a coordinated activity to compare reanalysis data sets using a variety of key diagnostics. The objectives of this project are to identify differences among reanalyses and understand their underlying causes, to provide guidance on appropriate usage of various reanalysis products in scientific studies, particularly those of relevance to SPARC, and to contribute to future improvements in the reanalysis products by establishing collaborative links between reanalysis centres and data users. The project focuses predominantly on differences among reanalyses, although studies that include operational analyses and studies comparing reanalyses with observations are also included when appropriate. The emphasis is on diagnostics of the upper troposphere, stratosphere, and lower mesosphere. This paper summarizes the motivation and goals of the S-RIP activity and extensively reviews key technical aspects of the reanalysis data sets that are the focus of this activity. The special issue The SPARC Reanalysis Intercomparison Project (S-RIP) in this journal serves to collect research with relevance to the S-RIP in preparation for the publication of the planned two (interim and full) S-RIP reports.

The latitudinal–vertical structure and the seasonal variation of the diurnal migrating tide (DW1) from the troposphere to the lower mesosphere are investigated, using reanalysis data from the Modern Era Retrospective analysis for Research and Applications (MERRA) and a linear tidal model. For the latitudinal-vertical structure, the observed feature is well represented by the four lowest-order classical Hough modes each of which shows its own unique vertical propagation characteristics. The tropospheric profile of DW1 temperature in the tropics is found to be mainly controlled by the first symmetric propagating Hough mode. The constant phase in the troposphere is due to the small static stability in the troposphere. For the seasonal variation, the amplitude from the stratosphere to the lower mesosphere maximizes at solstices. This is caused by a major contribution from the anti-symmetric propagating Hough mode. It is found that this seasonal variation is not explained by that of diabatic heating. Using a linear model, we found that background zonal wind is important for the seasonality. Also, using a modified mode-coupling approach, we interpret that in addition to primary tides generated by diabatic heating, secondary tides generated by meridional advection of background zonal momentum have a large contribution to the DW1, creating the above-mentioned seasonal variation from the stratosphere to the lower mesosphere in the tropics. It is suggested that both excitation and propagation characteristics can be physically interpreted in terms of the superposition of independent classical Hough modes. That is, each Hough mode is not only primarily excited by diabatic heating but also secondarily by mechanical forcing, and then propagates by following its own vertical propagation characteristics.

We observed ozone (O3) in the vertical region between 250 and 0.0005 hPa (~ 12–96 km) using the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on the Japanese Experiment Module (JEM) of the International Space Station (ISS) between 12 October 2009 and 21 April 2010. The new 4 K superconducting heterodyne receiver technology of SMILES allowed us to obtain a one order of magnitude better signal-to-noise ratio for the O3 line observation compared to past spaceborne microwave instruments. The non-sun-synchronous orbit of the ISS allowed us to observe O3 at various local times. We assessed the quality of the vertical profiles of O3 in the 100–0.001 hPa (~ 16–90 km) region for the SMILES NICT Level 2 product version 2.1.5. The evaluation is based on four components: error analysis; internal comparisons of observations targeting three different instrumental setups for the same O3 625.371 GHz transition; internal comparisons of two different retrieval algorithms; and external comparisons for various local times with ozonesonde, satellite and balloon observations (ENVISAT/MIPAS, SCISAT/ACE-FTS, Odin/OSIRIS, Odin/SMR, Aura/MLS, TELIS). SMILES O3 data have an estimated absolute accuracy of better than 0.3 ppmv (3%) with a vertical resolution of 3–4 km over the 60 to 8 hPa range. The random error for a single measurement is better than the estimated systematic error, being less than 1, 2, and 7%, in the 40–1, 80–0.1, and 100–0.004 hPa pressure regions, respectively. SMILES O3 abundance was 10–20% lower than all other satellite measurements at 8–0.1 hPa due to an error arising from uncertainties of the tangent point information and the gain calibration for the intensity of the spectrum. SMILES O3 from observation frequency Band-B had better accuracy than that from Band-A. A two month period is required to accumulate measurements covering 24 h in local time of O3 profile. However such a dataset can also contain variation due to dynamical, seasonal, and latitudinal effects.

Variation in stratospheric water vapor is controlled mainly by the dehydration process in the tropical tropopause layer (TTL) over the western Pacific; however, this process is poorly understood. To address this shortcoming, in this study the match method is applied to quantify the dehydration process in the TTL over the western Pacific. The match pairs are sought from the Soundings of Ozone and Water in the Equatorial Region (SOWER) campaign network observations using isentropic trajectories. For the pairs identified, extensive screening procedures are performed to verify the representativeness of the air parcel and the validity of the isentropic treatment, and to check for possible water injection by deep convection, consistency between the sonde data and analysis field, and conservation of the ozone content. Among the pairs that passed the screening test, we found some cases corresponding to the first quantitative value of dehydration associated with horizontal advection in the TTL. The statistical features of dehydration for the air parcels advected in the lower TTL are derived from the match pairs. Match analysis indicates that ice nucleation starts before the relative humidity with respect to ice (RHice) reaches 207 ± 81% (1σ) and that the air mass is dehydrated until RHice reaches 83 ± 30% (1σ). The efficiency of dehydration is estimated as the relaxation time required for the relative humidity of the supersaturated air parcel to approach the saturation state. This is empirically estimated from the match pairs as the quantity that reproduces the second water vapor observation, given the first observed water vapor amount and the history of the saturation mixing ratio of the match air mass exposed during the advection. The relaxation time is found to range from 2 to 3 h, which is consistent with previous studies.

The Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) onboard the International Space Station provided global measurements of ozone profiles in the middle atmosphere from 12 October 2009 to 21 April 2010. We present validation studies of the SMILES version 2.1 ozone product based on coincidence statistics with satellite observations and outputs of chemistry and transport models (CTMs). Comparisons of the stratospheric ozone with correlative data show agreements that are generally within 10%. In the mesosphere, the agreement is also good and better than 30% even at a high altitude of 73km, and the SMILES measurements with their local time coverage also capture the diurnal variability very well. The recommended altitude range for scientific use is from 16 to 73km. We note that the SMILES ozone values for altitude above 26km are smaller than some of the correlative satellite datasets; conversely the SMILES values in the lower stratosphere tend to be larger than correlative data, particularly in the tropics, with less than 8% difference below similar to 24km. The larger values in the lower stratosphere are probably due to departure of retrieval results between two detection bands at altitudes below 28km; it is similar to 3% at 24km and is increasing rapidly down below.

[1] Seasonal and subseasonal variations in the ozone mixing ratio (OMR) are investigated by using continuous 7 year ozonesonde data from Hanoi (21°N, 106°E), Vietnam. The mean seasonal variations for the 7 years show large amplitude at the upper troposphere and lower stratosphere (UTLS) region (10–18 km) and at the lower troposphere (around 3 km) with standard deviations normalized by the annual mean value of about 30% for both regions. In the UTLS region, the seasonal variation in the OMR shows a minimum in winter and a maximum in spring to summer. The variation seems to be caused by the seasonal change in horizontal transport. Low OMR air masses are transported from the equatorial troposphere in winter by the anticyclonic flow associated with the equatorial convections, and high OMR air masses are transported from the midlatitude stratosphere in summer possibly due to Rossby wave breakings in the UT region and anticyclonic circulation associated with the Tibetan High in the LS region. In the lower troposphere, a spring maximum is found at 3 km height. Biomass burning and tropopause foldings are suggested as possible causes of this maximum. Subseasonal variations in the OMR show large amplitude in the UTLS region (at around 15 km) and in the boundary layer (below 1 km) with the standard deviations normalized by the annual mean larger than 40%. The OMR variations in the winter UTLS region have a negative correlation with the meridional wind. This relation indicates that the low OMRs observed at Hanoi has been transported from the equatorial region.

[1] Considerable uncertainties remain in the global pattern of diurnal variation in stratospheric ozone, particularly lower to middle stratospheric ozone, which is the principal contributor to total column ozone. The Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) attached to the Japanese Experiment Module (JEM) on board the International Space Station (ISS) was developed to gather high-quality global measurements of stratospheric ozone at various local times, with the aid of superconducting mixers cooled to 4K by a compact mechanical cooler. Using the SMILES dataset, as well as data from nudged chemistry-climate models (MIROC3.2-CTM and SD-WACCM), we show that the SMILES observational data have revealed the global pattern of diurnal ozone variations throughout the stratosphere. We also found that these variations can be explained by both photochemistry and dynamics. The peak-to-peak difference in the stratospheric ozone mixing ratio (total column ozone) reached 8% (1%) over the course of a day. This variation needs to be considered when merging ozone data from different satellite measurements and even from measurements made using one specific instrument at different local times.

A new temperature-dependence correction (T-D correction) for Meisei RS2-91, RS-01G, and RS-06G radiosonde relative humidity (RH) measurements has been developed recently to remove the artificial stepwise change of ~3% RH at 0°C associated with the present (original) correction. These radiosondes have been used at most of the Japanese upper-air stations since the 1990s. The historical radiosonde humidity records at Sapporo and Tateno stations on the 925, 700, and 500 hPa pressure levels show apparent large downward trends between 1999 and 2009. This is because the original T-D correction has only been applied since February 2003 after a moist bias was discovered. The new T-D correction is found to result in a much smaller downward RH trend at Sapporo and almost no trend at Tateno.

The climate research community uses atmospheric reanalysis data sets to understand a wide range of processes and variability in the atmosphere, yet different reanalyses may give very different results for the same diagnostics. The Stratosphere–troposphere Processes And their Role in Climate (SPARC) Reanalysis Intercomparison Project (S-RIP) is a coordinated activity to compare reanalysis data sets using a variety of key diagnostics. The objectives of this project are to identify differences among reanalyses and understand their underlying causes, to provide guidance on appropriate usage of various reanalysis products in scientific studies, particularly those of relevance to SPARC, and to contribute to future improvements in the reanalysis products by establishing collaborative links between reanalysis centres and data users. The project focuses predominantly on differences among reanalyses, although studies that include operational analyses and studies comparing reanalyses with observations are also included when appropriate. The emphasis is on diagnostics of the upper troposphere, stratosphere, and lower mesosphere. This overview paper for the S-RIP special issue summarizes the motivation and goals of the S-RIP activity, and reviews key technical aspects of the reanalysis data sets that are the focus of the S-RIP report.

A meteorological balloon-borne cloud sensor called the Cloud Particle Sensor (CPS) has been developed. The CPS is equipped with a diode laser at ~ 790 nm and two photo detectors, with a polarization plate in front of one of the detectors, to count the number of particles per second and to obtain the cloud phase information (i.e. liquid, ice, or mixed). The lower detection limit for particle size was evaluated in laboratory experiments as ~ 2 μm diameter for water droplets. For the current model the output voltage often saturates for water droplets with diameter equal to or greater than ~ 80 μm. The upper limit of the directly measured particle number concentration is ~ 2 cm−3 (2 × 103L−1), which is determined by the volume of the detection area of the instrument. In a cloud layer with a number concentration higher than this value, particle signal overlap and multiple scattering of light occur within the detection area, resulting in a counting loss, though a partial correction may be possible using the particle signal width data. The CPS is currently interfaced with either a Meisei RS-06G radiosonde or a Meisei RS-11G radiosonde that measures vertical profiles of temperature, relative humidity, height, pressure, and horizontal winds. Twenty-five test flights have been made between 2012 and 2015 at midlatitude and tropical sites. In this paper, results from four flights are discussed in detail. A simultaneous flight of two CPSs with different instrumental configurations confirmed the robustness of the technique. At a midlatitude site, a profile containing, from low to high altitude, water clouds, mixed phase clouds, and ice clouds was successfully obtained. In the tropics, vertically thick cloud layers in the middle to upper troposphere and vertically thin cirrus layers in the upper troposphere were successfully detected in two separate flights. The data quality is much better at night, dusk and dawn than during the daytime because strong sunlight affects the measurements of scattered light.

A method of correction for radiosonde pressure and temperature data by using simultaneous global positioning system (GPS) ellipsoidal height (zGPS) is proposed. The correction is made by adjusting the observed pressure and temperature so that the ellipsoidal height (zPTU) calculated from integrating the hypsometric equation by using the latitude- and altitude-dependent gravity together with the observed pressure, temperature and humidity (PTU) agrees with zGPS. The temperature bias is assumed to arise only from inaccurate radiation correction so that there is no temperature bias in the nighttime data. Under this assumption, the deviations of zPTU from zGPS in the nighttime data result only from observational errors in pressure. The pressure adjustment required to remove these deviations is applied also to the daytime data. The daytime temperature bias can then be estimated from the difference between zPTU and zGPS during the day. The biases in Vaisala RS80 pressure and temperature measurements are estimated using the Soundings of Ozone and Water in the Equatorial Region campaign data. The estimated pressure bias is positive below ∼7 km and negative above it. The bias above 15 km is statistically significant. The daytime temperature bias lacks statistical significance due to fluctuations in the results.

Structure and variability of the tropical tropopause are presented using radio occultation measurements by CHAMP/GPS (CHAllenging Mini satellite Payload/ Global Positioning System) from May 2001 to December 2004 (with a total of 175,149 occultations). The tropopause heights defined by both lapse rate and cold point generally show large-scale, off-equatorial maxima (tropopause increase at 20°N or S than at equator), and sometimes even a high tropopause for about 0.3 to 0.65 km (on an average) at 20°N and S simultaneously than at the equator along a particular meridian, in contrast to our previous knowledge. Although this feature has already been reported partially during the summer monsoon season, the present study shows the seasonal and geographical distributions of the tropical tropopause comprehensively using a new promising observational technique. In addition, the vertical shape of the tropopause is found to be sharp in the equatorial region and broad in the subtropics especially in northern winter. Possible mechanisms are discussed in light of dynamical and radiative processes.

Ozonesonde observation campaigns were conducted over the Indonesian maritime continent in September–October 1998 and in August–September 1999. Three stations were used for each campaign, Watukosek (7.5°S,112.6°E), Kototabang (0.20°S,100.3°E), and Pontianak (0.03°N,109.3°E) for the 1998 campaign, and Watukosek, Kototabang, and Darwin (12.25°S,130.55°E) for the 1999 campaign. Both periods were basically characterized as the La Nina period, and the tropospheric ozone concentrations showed normal values. Temporal variation and horizontal distribution of an ozone layered structure with a 1–1.5-km thickness were obtained just below the tropopause at the two equatorial stations during the 1998 campaign. Meteorological data analyses including the reverse domain filling technique suggested that the most plausible explanation for the layer is the quasi-horizontal, thin intrusion from the northern midlatitude lower stratosphere associated with a breaking Rossby wave and large-scale flow pattern.