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Stratospheric water vapor is known to have decreased suddenly at around the year 2000 to 2001 after a prolonged increase through the 1980s and 1990s. This stepwise change is studied by examining the entry value of water to the stratosphere ([H2O]e) and some Lagrangian diagnostics of dehydration taking place in the Tropical Tropopause Layer (TTL). The analysis is made using the backward kinematic trajectories initialized every ~ 10 days since January 1997 till December 2002 on 400K potential temperature surface in the tropics. The [H2O]e is estimated by the ensemble mean value of the water saturation mixing ratio (SMR) at the Lagrangian cold point (LCP) 10 where SMR takes minimum (SMRmin) in the TTL before reaching the 400 K surface. The drop in [H2O]e is identified to have occurred in September 2000. The horizontal projection of September trajectories, tightly trapped by anticyclonic circulation around Tibetan high, shows eastward expansion since the year 2000. Associated changes are measured by three-dimensional bins, each having the dimension of 10° longitude 15 by 10° latitude within the TTL. The probability distribution of LCPs shows appreciable change exhibiting a composite pattern of two components: (i) the dipole structure consisting of the decrease over the Bay of Bengal and Malay Peninsula and the increase over the northern subtropical western Pacific and (ii) the decrease over the equatorial western Pacific and the increase over the central Pacific almost symmetric with 20 respect to the equator. The SMRmin shows general decrease in the tropics with some enhancement in the central Pacific. The expectation values, defined by the multiple of the probability of LCP events and the ensemble mean values of SMRmin, are calculated on each bin for both periods prior and posterior to the drop. These values are the spatial projection of [H2O]e on individual bin. The results indicate that the drop is 25 brought about by the decrease of water transport borne by the air parcels having experienced the LCP over the Bay of Bengal and the western tropical Pacific. The former is related to the eastward expansion of the anticyclonic circulation around the weakened Tibetan high, while the latter will be linked to the eastward expansion of western tropical warm water to the central Pacific. This oceanic surface forcing may be responsible also for the modulation of dehydration efficiency in the successive northern winter. The drop in September 2000 and the sustained low values thereafter of [H2O]e are thus interpreted as being driven by the changes in thermal forcing from the continental and 5 oceanic bottom boundaries. [ABSTRACT FROM AUTHOR]

Previous research has found that conventional radiosondes equipped with a traditional pressure sensor can be subject to a pressure bias, particularly in the stratosphere. This study examines this pressure bias and the resulting altitude misestimation, and its impact on temperature, ozone, and water vapor profiles is considered using data obtained between December 2003 and January 2010 during the Soundings of Ozone andWater in the Equatorial Region (SOWER) campaigns. The payload consisted of a radiosonde (Vaisala RS80), ozone and water vapor sondes, and a global positioning system (GPS) sensor. More than 30 soundings are used in this study. As GPS height data are thought to be highly accurate, they can be used to calculate pressure. The RS80 pressure bias in the tropical stratosphere is estimated to be -0.4±0.2 hPa (1σ) between 20 and 30 km. As this pressure bias is negative throughout the stratosphere, it leads to systematic overestimation of geopotential height by 43±23, 110±40, and 240±92m (1σ) at 20, 25, and 30 km, respectively when it is calculated by using the hypsometric equation. Because of the altitude overestimation, we see some offsets in observation parameters having a vertical gradient such as temperature, ozone, and water vapor. Those offsets in the meteorological soundings obtained using the RS80 may have generated an artificial trend in the meteorological records when radiosondes were changed from the RS80, which had no GPS unit, to the new ones with a GPS unit. Therefore, it is important to take those offsets into account in climate change studies. [ABSTRACT FROM AUTHOR]

In submitting data to the World Meteorological Organization (WMO) World Ozone and Ultraviolet Data Center (WOUDC), numerous ozonesonde stations include a correction factor (CF) that multiplies ozone concentration profile data so that the columns computed agree with column measurements from co-located ground-based and/or overpassing satellite instruments. We evaluate this practice through an examination of data from four Japanese ozonesonde stations: Kagoshima, Naha, Sapporo, and Tsukuba. While agreement between the sonde columns and Total Ozone Mapping Spectrometer (TOMS) or Ozone Mapping Instrument (OMI) is improved by use of the CF, agreement between the sonde ozone concentrations reported near the surface and data from surface monitors near the launch sites is negatively impacted. In addition, we find the agreement between the mean sonde columns without the CF and the ground-based Dobson instrument columns is improved by ~1.5% by using the McPeters et al. (1997) balloon burst climatology rather than the constant mixing ratio assumption (that has been used for the data in the WOUDC archive) for the above burst height column estimate. Limited comparisons of coincident ozonesonde profiles from Hokkaido University with those in the WOUDC database suggest that while the application of the CFs in the stratosphere improves agreement, it negatively impacts the agreement in the troposphere. Finally and importantly, unexplained trends and changing trends in the CFs appear over the last 20 years. The overall trend in the reported CFs for the four Japanese ozonesonde stations from 1990-2010 is (-0.264 ± 0.036) x 10-2 yr-1; but from 1993-1999 the trend is (-2.18 ± 0.14) x 10-2 yr-1 and from 1999-2009 is (1.089 ± 0.075) x 10-2 yr-1, resulting in a statistically significant difference in CF trends between these two periods of (3.26 ± 0.16) x 10-2 yr-1. Repeating the analysis using CFs derived from columns computed using the balloon-burst climatology, the trends are somewhat reduced, but remain statistically significant. Given our analysis, we recommend the following: (1) use of the balloon burst climatology is preferred to a constant mixing ratio assumption for determining total column ozone with sonde data; (2) if CFs are applied, their application should probably be restricted to altitudes above the tropopause; (3) only sondes that reach at least 32 km (10.5 hPa) before bursting should be used in data validation and/or ozone trend studies if the constant mixing ratio assumption is used to calculate the above burst column (as is the case for much of the data in the WOUDC archive). Using the balloon burst climatology, sondes that burst above 29 km (~16 hPa), and perhaps lower, can be used; and (4) all ozone trend studies employing Japanese sonde data should be revisited after a careful examination of the impact of the CF on the calculated ozone trends. [ABSTRACT FROM AUTHOR]

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% (1 σ) 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. [ABSTRACT FROM AUTHOR]

A network of balloon-born radiosonde observations employing chilled-mirror hygrometers for water and electrochemical concentration cells for ozone has been operated since late 1990s in the Tropical Pacific trying to capture the progress of dehydration for the air parcels advected horizontally in the Tropical Tropopause Layer (TTL). The analyses of this dataset are made on isentropes taking advantage of the conservative properties of tracers in adiabatic motion. The existence of ice particles is diagnosed by lidars simultaneously operated with sonde flights. Characteristics of the TTL dehydration are presented on the basis of individual soundings and statistical features. Supersaturations close to 80% in the relative humidity with respect to ice (RHice) have been observed in subvisible cirrus clouds located near the cold point tropopause at extremely low temperatures around 180 K. Further observational evidence is needed to confirm the credibility of such high values of RHice. The progress of TTL dehydration is reflected in isentropic scatter plots between the sonde-observed mixing ratio (OMR) and the minimum saturation mixing ratio (SMRmin) along the back trajectories associated with the observed air mass. The supersaturation exceeding the critical value of the homogeneous ice nucleation (OMR > 1.6xSMRmin) is frequently observed on 360 and 365 K surfaces indicating that the cold trap dehydration is under progress in the TTL. The near correspondence between the two (OMR~SMRmin) on 380 K on the other hand implies that this surface is not significantly cold for the advected air parcels to be dehydrated. Above 380 K, the cold trap dehydration would scarcely function while some moistening in turn occurs before the air parcels reach the lowermost stratosphere at around 400 K where OMR is generally smaller than SMRmin. [ABSTRACT FROM AUTHOR]

In submitting data to the World Meteorological Organization (WMO) World Ozone and Ultraviolet Data Center (WOUDC), numerous ozonesonde stations include a correction factor (CF) that multiplies ozone concentration profile data so that the columns computed agree with column measurements from co-located ground-based and/or overpassing satellite instruments. We evaluate this practice through an examination of data from 4 Japanese ozonesonde stations: Kagoshima, Naha, Sapporo, and Tsukuba. While agreement between the sonde columns and Total Ozone Mapping Spectrometer (TOMS) or Ozone Mapping Instrument (OMI) is improved by use of the CF, agreement between the sonde ozone concentrations reported near the surface and data from surface monitors near the launch sites is negatively impacted. In addition, the agreement between the mean sonde columns without the CF and the ground-based Dobson instrument columns is improved by ~1.5% by using the McPeters et al. (1997) balloon burst climatology rather than the constant mixing ratio assumption for the above burst height column estimate. Limited comparisons of coincident ozonesonde profiles from Hokkaido University with those in the WOUDC database suggest that while the application of the CFs in the stratosphere improves agreement, it negatively impacts the agreement in the troposphere. Finally, unexplained trends and changing trends in the CFs appear over the last 20 yr. The overall trend in the CFs for the four Japanese ozonesonde stations from 1990-2010 is (-0.157±0.032)×10-2 yr-1; but from 1993-1999 the trend is (-2.21±0.14)×10-2 yr-1 and from 1999-2009 is (1.180±0.059)×10-2 yr-1, resulting in a statistically significant difference in CF trends between these two periods of (3.39±0.15)×10-2 yr-1. Given our analysis, we recommend the following: (1) use of the balloon burst climatology is preferred to a constant mixing ratio assumption for determining total column ozone with sonde data; (2) if CFs are applied, their application should probably be restricted to altitudes above the tropopause; (3) only sondes that reach at least 32 km (10.5 hPa) before bursting should be used in data validation and/or ozone trend studies; and (4) all ozone trend studies employing Japanese sonde data should be revisited after a careful examination of the impact of the CF on the calculated ozone trends. [ABSTRACT FROM AUTHOR]

The article reports on the development of a fast-response high-resolution temperature sonde intended to meet the scientific requirements for climate change research. Topics include the important function of stratosphere on climate, how the persistent changes in the tropospheric flow accompany the changes in the strength of the winter-time stratospheric polar vortex and the benefits of using fast-responding sensors. Also discussed is the contribution of test flights to contamination.

Water vapor observations by chilled-mirror hygrometers were conducted at Bandung, Indonesia (6.90°S, 107.60°E) and Tarawa, Kiribati (1.35°N, 172.91°E) in December 2003 to examine the efficiency of dehydration during horizontal advection in the tropical tropopause layer (TTL). Trajectory analyses based on bundles of isentropic trajectories suggest that the modification of air parcels' identity due to irreversible mixing by the branching-out and merging-in of nearby trajectories is found to be an important factor, in addition to the routes air parcels follow, for interpreting the water vapor concentrations observed by chilled-mirror frostpoint hygrometers in the TTL. Clear correspondence between the observed water vapor concentration and the estimated temperature history of air parcels is found showing that drier air parcels were exposed to lower temperatures than were more humid ones during advection. Although the number of observations is quite limited, the water content in the observed air parcels on many occasions was more than that expected from the minimum saturation mixing ratio during horizontal advection prior to sonde observations. [ABSTRACT FROM AUTHOR]

Water vapor sonde observations were conducted at Bandung, Indonesia (6.90° S, 107.60° E) and Tarawa, Kiribati (1.35° N, 172.91° E) in December 2003 to examine the efficiency of the "cold trap" dehydration in the tropical tropopause layer (TTL). Trajectory analysis based on bundles of trajectories suggest that the modification of air parcels' identity due to irreversible mixing by the branching-out and merging-in of nearby trajectories is found to be an important factor, in addition to the routes air parcels are supposed to follow, for interpreting the water vapor concentrations observed by radiosondes in the TTL. Clear correspondence between the observed water vapor concentration and the estimated temperature history of air parcels is found showing that dry air parcels are exposed to low temperatures while humid air parcels do not experience cold conditions during advection, in support of the "cold trap" hypothesis. It is suggested that the observed air parcel retained the water vapor by roughly twice as much as the minimum saturation mixing ratio after its passage through the "cold trap," although appreciable uncertainties remain. [ABSTRACT FROM AUTHOR]