A polarization lidar was continuously operated aboard the research vessel Mirai in the tropical western Pacific over three northern winters: at 2.0°N, 138.0°E during November and December 2001; at ...2.0°N, 138.5°E during November and December 2002; and at 7.5°N, 134.0°E during December 2004 and January 2005. Intensive radiosonde soundings were made from the vessel at 3‐h intervals during all three campaigns. The mechanisms that underlie the observed variations in cirrus in the tropical tropopause layer (TTL) are discussed from the viewpoint of large‐scale dynamics and transport. During the 2001 campaign, the tropopause region was cold, but the TTL was often clear, with only some subvisual cirrus. Potential vorticity data and trajectories show that the TTL during this period was strongly affected by dry air transport from the northern midlatitude lower stratosphere. During the 2002 campaign, a packet of large‐amplitude equatorial Kelvin waves was the primary control on the generation and disappearance of cirrus in the TTL. During the 2004–2005 campaign, a cold phase of large‐scale waves resulted in cirrus generation in the TTL in late December of 2004, similar to that observed during the 2002 campaign. Outflow from the South Pacific Convergence Zone (SPCZ) caused optically thick cirrus in the TTL, particularly during early January 2005, when we also observed regular diurnal variations in cirrus development within the TTL, that is, apparent sedimentation during the nighttime. We investigated two possible controlling processes, namely, horizontal advection together with diurnal variations in convective activity within the SPCZ and diurnal variations in local temperature due to tides and gravity waves. In the equatorial western Pacific, equatorial Kelvin waves are the important dynamical process that controls cirrus variations in the TTL. Dry‐air horizontal transport from the midlatitude lower stratosphere and wet‐air vertical transport near the tropical convergence regions should also be considered in fully explaining the cirrus observations in the TTL.
Chikungunya virus (CHIKV) and Ross River virus (RRV) of the genus Alphavirus, family Togaviridae are mainly transmitted by Aedes mosquitoes and the symptoms they cause in patients are similar to ...dengue. A chikungunya (CHIK) outbreak re-emerged in several Asian countries during 2005–2006. This study aimed to clarify the prevalence of CHIKV infection in suspected dengue patients in six countries in South Asia and Southeast Asia. Seven hundred forty-eight serum samples were from dengue-suspected patients in South Asia and Southeast Asia, and 52 were from patients in Fiji. The samples were analysed by CHIKV IgM capture ELISA, CHIKV IgG indirect ELISA and focus reduction neutralization test against CHIKV or RRV. CHIK-confirmed cases in South Asia, particularly Myanmar and Sri Lanka, were 4·6%, and 6·1%, respectively; and in Southeast Asia, particularly Indonesia, the Philippines and Vietnam, were 27·4%, 26·8% and 25·0%, respectively. It suggests that CHIK was widely spread in these five countries in Asia. In Fiji, no CHIK cases were confirmed; however, RRV-confirmed cases represented 53·6% of suspected dengue cases. It suggests that RRV is being maintained or occasionally entering from neighbouring countries and should be considered when determining a causative agent for dengue-like illness in Fiji.
The gravitational
separation of major atmospheric components, in addition to the age of air,
would provide additional useful information about stratospheric circulation.
However, observations of the ...age of air and gravitational separation are
still geographically sparse, especially in the tropics. In order to address
this issue, air samples were collected over Biak, Indonesia in February 2015
using four large plastic balloons, each loaded with two compact cryogenic
samplers. With a vertical resolution of better than 2 km, air samples from
seven different altitudes were analyzed for CO2 and SF6 mole
fractions, δ15N of N2, δ18O of O2, and δ(Ar∕N2) to examine the vertically dependent age and
gravitational separation of air in the tropical tropopause layer (TTL) and
the equatorial stratosphere. By comparing their measured mole fractions with
aircraft observations in the upper tropical troposphere, we have found that
CO2 and SF6 ages increase gradually with increasing altitude from
the TTL to 22 km, and then rapidly from there up to 29 km. The CO2 and
SF6 ages agree well with each other in the TTL and in the lower
stratosphere, but show a significant difference above 24 km. The average
values of δ15N of N2, δ18O of O2, and δ(Ar∕N2) all show a small but distinct upward decrease due to the
gravitational separation effect. Simulations with a two-dimensional
atmospheric transport model indicate that the gravitational separation effect
decreases as tropical upwelling is enhanced. From the model calculations with
enhanced eddy mixing, it is also found that the upward increase in air age is
magnified by horizontal mixing. These model simulations also show that the
gravitational separation effect remains relatively constant in the lower
stratosphere. The results of this study strongly suggest that the
gravitational separation, combined with the age of air, can be used to
diagnose air transport processes in the stratosphere.
Japanese encephalitis is a severe disease of acute encephalitis, with children and the elderly primarily affected, and with mortality rates reaching over 25%. The virus is transmitted mainly by ...species of the Culex (Culex) vishnui subgroup, primarily the widely spread Cx. tritaeniorhynchus Giles. The latter is known as a highly migratory mosquito which moves with airflow over large distances. We explored the geometric variation of the wing venation among distant areas of its geographic distribution. Our working hypothesis was that shape variation across geography could reveal known past and present migratory routes.
We compared the wing venation geometry of 236 female Culex tritaeniorhynchus from different locations in the Madagascan (La Reunion), Oriental (Thailand, Vietnam) and Paleartic (Japan) regions. To ascertain the taxonomic signal of the wing venation we also used two species as relative outgroups, Cx. whitmorei and Cx. brevipalpis.
In spite of an increasing morphometric variation as expected with larger geographic dispersion, our Cx. tritaeniorhynchus samples were clustered as a single species when considered relative to other Culex species. The relationships between geographic sites of Cx. tritaeniorhynchus globally conformed with an isolation by distance model. The shape homogeneity of our Palearctic samples (Japan) contrasted with some heterogeneity observed in the Oriental region (Thailand, Vietnam), and could be related to the different regimes of wind trajectories in these regions.
The average shape variation of Culex tritaeniorhynchus disclosed a separation between Madagascan, Oriental and Palearctic regions in accordance with geography. The wing venation not only could reflect geography, it also contained a clear taxonomic signal separating three Culex species. Within Cx. tritaeniorhynchus, a contrasting pattern of shape variation between the Palearctic and the Oriental regions is tentatively explained by the influence of wind trajectories.
•Wing shape variation of Cx. tritaeniorhynchus was examined by a landmark study•The wing venation contained a clear taxonomic and geographic signal.•The Palearctic and Oriental regions showed a contrasting pattern of shape variation.•This pattern was tentatively explained by the influence of wind trajectories
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 and Water 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 plus or minus 0.2 hPa (1 sigma ) between 20 and 30 km. As this pressure bias is negative throughout the stratosphere, it leads to systematic overestimation of geopotential height by 43 plus or minus 23, 110 plus or minus 40, and 240 plus or minus 92 m (1 sigma ) 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.
Bromoform (CHBr3), dibromochloromethane (CHBr2Cl), and dibromomethane (CH2Br2) in the atmosphere were measured at various sites, including tropical islands, the Arctic, and the open Pacific Ocean. Up ...to 40 ppt of bromoform was observed along the coasts of tropical islands under a sea breeze. Polybromomethane concentrations were highly correlated among the coastal samples, and the ratios CH2Br2/CHBr3 and CHBr2Cl/CHBr3 showed a clear tendency to decrease with increasing CHBr3 concentration. These findings are consistent with the observations that polybromomethanes are emitted mostly from macroalgae whose growth is highly localized to coastal areas and that CHBr3 has the shortest lifetime among these three compounds. The relationship between the concentration ratios CHBr3/CH2Br2 and CHBr2Cl/CH2Br2 suggested a large mixing/dilution effect on bromomethane ratios in coastal regions and yielded a rough estimate of 9 for the molar emission ratio of CHBr3/CH2Br2 and of 0.7 for that of CHBr2Cl/CH2Br2. Using these ratios and an global emission estimate for CH2Br2 (61 Gg/yr (Br)) calculated from its background concentration, the global emission rates of CHBr3 and CHBr2Cl were calculated to be approximately 820(±310) Gg/yr (Br) and 43(±16) Gg/yr (Br), respectively, assuming that the bromomethanes ratios measured in this study are global representative. The estimated CHBr3 emission is consistent with that estimated in a very recent study by integrating the sea‐to‐air flux database. Thus the contribution of CHBr3 and CHBr2Cl to inorganic Br in the atmosphere is likely to be more important than previously thought.
We apply the match technique, whereby the same air mass is observed more than once and such cases are termed a "match", to study the dehydration process associated with horizontal advection in the ...tropical tropopause layer (TTL) over the western Pacific. The matches are obtained from profile data taken by the Soundings of Ozone and Water in the Equatorial Region (SOWER) campaign network observations using isentropic trajectories calculated from European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses. For the matches 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 referring to the ozone conservation. Among the matches that passed the screening tests, we identified 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 matches. The threshold of nucleation is estimated to be 146 ± 1% (1σ) in relative humidity with respect to ice (RHice), while dehydration seems to continue until RHice reaches about 75 ± 23% (1σ) in the altitude region from 350 to 360 K. The efficiency of dehydration expressed by the relaxation time required for the supersaturated air parcel to approach saturation is empirically determined from the matches. A relaxation time of approximately one hour reproduces the second water vapor observation reasonably well, given the first observed water vapor amount and the history of the saturation mixing ratio during advection in the lower TTL.
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 similar to 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 plus or minus 0.036) x 10 super(-2) yr super(-1); but from 1993-1999 the trend is (-2.18 plus or minus 0.14) x 10 super(-2) yr super(-1) and from 1999-2009 is (1.089 plus or minus 0.075) x 10 super(-2) yr super(-1), resulting in a statistically significant difference in CF trends between these two periods of (3.26 plus or minus 0.16) x 10 super(-2) yr super(-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 ( similar to 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.
A network of balloon-borne radiosonde observations employing chilled-mirror hygrometers for water and electrochemical concentration cells for ozone has been operated since the late 1990s in the ...Tropical Pacific to capture the evolution of dehydration of air parcels advected quasi-horizontally in the Tropical Tropopause Layer (TTL). The analysis of this dataset is made on isentropes taking advantage of the conservative properties of tracers moving adiabatically. 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 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. Although further observational evidence is needed to confirm the credibility of such high values of RHice, the evolution of TTL dehydration is evident from the data 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. Supersaturation exceeding the critical value of homogeneous ice nucleation (OMR > 1.6 × SMRmin) is frequently observed on the 360 and 365 K surfaces indicating that cold trap dehydration is in progress in the TTL. The near correspondence between the two (OMR ~ SMRmin) at 380 K on the other hand implies that this surface is not sufficiently cold for the advected air parcels to be dehydrated. Above 380 K, cold trap dehydration would scarcely function while some moistening occurs before the air parcels reach the lowermost stratosphere at around 400 K where OMR is generally smaller than SMRmin.
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