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We assess the performance of an isotope ratio infrared spectrometer (IRIS) to measure carbon (δ13 C) and oxygen (δ18 O) isotope ratios in atmospheric carbon dioxide (CO 2) and report observations from a 26 d field deployment trial at Baring Head, New Zealand, NIWA's atmospheric observatory for Southern Ocean baseline air. Our study describes an operational method to improve the performance in comparison to previous publications on this analytical instrument. By using a calibration technique that reflected the principle of identical treatment of sample and reference gases, we achieved a reproducibility of 0.07 ‰ for δ13 C-CO 2 and 0.06 ‰ for δ18 O-CO 2 over multiple days. This performance is within the extended compatibility goal of 0.1 ‰ for both δ13 C-CO 2 and δ18 O-CO 2 , which was recommended by the World Meteorological Organization (WMO). Further improvement in measurement performance is desirable to also meet the WMO network compatibility goals of 0.01 ‰ for δ13 C-CO 2 and 0.05 ‰ for δ18 O-CO 2 , which is needed to resolve the small variability that is typical for background air observatories such as Baring Head. One objective of this study was to assess the capabilities and limitations of the IRIS analyser to resolve δ13 C-CO 2 and δ18 O-CO 2 variations under field conditions. Therefore, we selected multiple events within the 26 d record for Keeling plot analysis. This resolved the isotopic composition of endmembers with an uncertainty of ≤ 1 ‰ when the magnitude of CO 2 signals is larger than 10 ppm. The uncertainty of the Keeling plot analysis strongly increased for smaller CO 2 events (2–7 ppm), where the instrument performance is the limiting factor and may only allow for the distinction between very different endmembers, such as the role of terrestrial versus oceanic carbon cycle processes. [ABSTRACT FROM AUTHOR]

A sensor based on tunable diode laser absorption spectroscopy was constructed for time-resolved temperature and water vapor concentration measurements in a scramjet combustor. The sensor probed two absorption lines near 1390 nm with two time-multiplexed lasers used to measure temperature and water vapor concentration at up to 20 kHz. A demonstration experiment was performed in the supersonic, expanding exhaust region of the combustor, showing the measurement to be repeatable, able to resolve temporal trends during tunnel operation, and sensitive to changes in combustor operating conditions. OCIS codes: 120.1740, 120.6780, 300.1030, 300.6260, 300.6340.

The factors driving variability in rainfall stable water isotopes (specifically δ18O and deuterium excess, d = δ2H − 8 δ18O) were studied in a 13‐year data set of daily rainfall samples from coastal southwestern Western Australia (SWWA). Backwards dispersion modeling, automatic synoptic type classification, and a statistical model were used to establish causes of variability on a daily scale; and predictions from the model were aggregated to longer temporal scales to discover the cause of variability on multiple timescales. Factors differ between δ18O and d and differ according to temporal scale. Rainfall intensity, both at the observation site and upwind, was most important for determining δ18O and this relationship was robust across all time scales (daily, seasonal, and interannual) as well as generalizing to a second observation site. The sensitivity of δ18O to rainfall intensity makes annual mean values particularly sensitive to the year's largest events. Projecting the rainfall intensity relationship back through ∼100 years of precipitation observations can explain ∼0.2 $0.2$–0.4‰ shifts in rainfall δ18O. Twentieth century speleothem records from the region exhibit signals of a similar magnitude, indicating that rainfall intensity should be taken into account during the interpretation of regional climate archives. For d, humidity during evaporation from the ocean was the most important driver of variability at the daily scale, as well as explaining the seasonal cycle, but source humidity failed to explain the longer‐term interannual variability. Plain Language Summary: In cave deposits, as with several other natural systems, the relative abundance of the heavy isotopes oxygen‐18 and deuterium can be used to determine past changes in climate. This is because the isotopic composition of these systems is linked to that of rainfall, while the abundance of heavy isotopes in rainfall is driven by climate parameters such as temperature and rainfall characteristics. For this to be possible, the factors which drive rainfall isotopic variability need to be well known. This study uses a 13‐year data set of daily rainfall samples from coastal southwestern Western Australia to better understand isotopic variability for this region. Oxygen‐18 variations here are driven mainly by rainfall intensity (the amount of rain each day) both according to measurements at the site and upwind simulations. Deuterium excess, a second order parameter which is often linked to conditions in the evaporation source region, was well‐predicted by source region humidity at the daily scale but not when aggregated to annual totals. The relationship between rainfall intensity and oxygen‐18 appears to be important over the 20th century, based on a comparison between observed rainfall and a cave record. Key Points: Precipitation δ18O variability is driven primarily by rainfall intensity in southwestern Western AustraliaInterannual δ18O variability is strongly influenced by the largest rainfall events of the yearHumidity during evaporation drives deuterium excess variability at a daily, but not interannual, timescale [ABSTRACT FROM AUTHOR]

Little overlap exists in the required capabilities of 222 Rn (radon) monitors for public health and atmospheric research. The former requires robust, compact, easily transportable instruments to characterise daily to yearly variability >100 Bq m -3 , whereas the latter requires static instruments capable of characterising sub-hourly variability between 0.1 and 100 Bq m -3. Consequently, detector development has evolved independently for the two research communities, and while many radon measurements are being made world-wide, the full potential of this measurement network can't be realised because not all results are comparable. Development of a monitor that satisfies the primary needs of both measurement communities, including a calibration traceable to the International System of Units (SI), would constitute an important step toward (i) increasing the availability of radon measurements to both research communities, and (ii) providing a means to harmonize and compare radon measurements across the existing eclectic global network of radon detectors. To this end, we describe a prototype detector built by the Australian Nuclear Science and Technology Organisation (ANSTO), in collaboration with the EMPIR 19ENV01 traceRadon Project and Physikalisch-Technische Bundesanstalt (PTB). This two-filter dual-flow-loop radon monitor can be transported in a standard vehicle, fits in a 19 ′′ instrument rack, has a 30 min temporal resolution, and a detection limit of ∼0.14 Bq m -3. It is capable of continuous, long-term, low-maintenance, low-power, indoor or outdoor monitoring with a high sensitivity and an uncertainty of ∼15 % at 1 Bq m -3. Furthermore, we demonstrate the successful transfer of an SI traceable calibration from this portable monitor to a 1500 L two-filter radon monitor under field conditions. [ABSTRACT FROM AUTHOR]

Aerosol measurements over the Southern Ocean have been identified as critical to an improved understanding of aerosol-radiation and aerosol-cloud interactions, as there currently exists significant discrepancies between model results and measurements in this region. Previous springtime measurements from the East Antarctic seasonal ice zone revealed a significant increase in aerosol number concentrations when crossing the atmospheric polar front into the Polar cell. A return voyage in summer 2017 made a more extensive range of aerosols measurements, including in particular aerosol number concentrations and submicron size distributions. Again, significantly greater aerosol number concentrations were observed in the Polar cell than in the Ferrel cell. Unlike the previous spring voyage however, the polar front was unable to be identified by a step change in aerosol concentration. A possible explanation is that atmospheric mixing across the polar front occurs to a greater degree in summer, therefore weakening the atmospheric boundary at the front. This atmospheric mixing in summer complicates the determination of the polar front location. These changes, together with the increased source of precursors from phytoplankton emissions, are likely to explain the seasonal differences observed in the magnitude of aerosol populations between the Ferrel and Polar cell. In the present analysis, meteorological variables were used to identify different air- masses and then aerosol measurements were compared based on these identifications. CN3 concentrations measured during wind directions indicative of Polar cell airmasses (median 594 cm-3) were larger than those measured during wind directions indicative of Ferrel cell air (median 265 cm-3). CN3 and CCN concentrations were larger during periods where the absolute humidity was less than 4.3 gH2O/ m3, indicative of free tropospheric or Antarctic continental airmasses, compared to other periods of the voyage. These results indicate that a persistently more concentrated aerosol population is present in the Polar cell over the East Antarctic seasonal ice zone, although the observed difference between the two cells may vary seasonally. [ABSTRACT FROM AUTHOR]

Terrestrial data spanning the Last Glacial Maximum (LGM) and deglaciation from the southern Australian region are sparse, and limited to discontinuous sedimentological and geomorphological records with relatively large chronological uncertainties. This dearth of records has prevented a critical assessment of the role of the Southern Hemisphere mid-latitude westerly winds on the region's climate during this time period. In this study, two precisely-dated speleothem records for Mairs Cave, Flinders Ranges, are presented, providing a detailed terrestrial hydroclimatic record for the southern Australian drylands during 23-15 ka for the first time. Enhanced recharge to Mairs Cave is interpreted from the speleothem record by the activation of growth, physical flood layering and δ18O and δ13C minima. Periods of lowered recharge are indicated by isotopic enrichment, primarily affecting δ18O, argued to be driven by evaporation of shallow soil/epikarst water in this water-limited environment. A hydrological driver is supported by calcite fabric changes. The Mairs Cave record indicates that the Flinders Ranges were relatively wet during the LGM and early deglaciation, particularly over the interval 18.9-16 ka. This wetter phase ended abruptly with a shift to drier conditions at 15.8 ka. These findings are in agreement with the geomorphic archives for this region, as well as the timing of events in records from the broader Australasian region. The recharge phases identified in the Mairs Cave record are correlated with, but antiphase to, the position of the westerly winds interpreted from a marine core in the Great Australian Bight. The implication is that the mid-latitude westerlies are located further south during the period of enhanced recharge in the Mairs Cave record (18.9-16 ka), and conversely are located further north when greater aridity is interpreted in the speleothem record. A comparison with speleothem records from the northern Australasian region reveals that the availability of sub-tropical/tropical moisture is the most likely explanation driving enhanced recharge, with further amplification of recharge occurring during the early half of Heinrich Stadial 1, possibly influenced by a more southerly-displaced Intertropical Convergence Zone (ITCZ). A rapid transition to aridity at 15.8 ka is consistent with a retraction of this tropical moisture source. [ABSTRACT FROM AUTHOR]

The stable isotopic composition of water vapour provides information about moisture sources and processes that is difficult to obtain with traditional measurement techniques. Recently, it has been proposed that the D-excess (dv = δ2H - 8 × δ18O) of water vapour can provide a diagnostic tracer of continental moisture recycling. However, D-excess exhibits a diurnal cycle that has been observed across a variety of ecosystems and may be influenced by a range of processes beyond regional scale moisture recycling, including local evaporation (ET) fluxes. There is a lack of measurements of D-excess in evaporation (ET) fluxes, which has made it difficult to assess how ET fluxes modify the D-excess in water vapour (dv). With this in mind, we employed a chamber based approach to directly measure D-excess in ET (dET) fluxes. We show that ET fluxes imposed a negative forcing on the ambient vapour and could not explain the higher daytime dv values. The low dET observed here was sourced from a soil water pool that had undergone an extended drying period, leading to low D-excess of the soil moisture. A strong correlation between daytime dv and locally measured relative humidity was consistent with an oceanic moisture source, suggesting that remote hydrological processes were the major contributor to daytime dv variability. During the early evening, ET fluxes into a shallow nocturnal inversion layer caused a lowering of the dv values near the surface. In addition, transient mixing of vapour with a higher D-excess from above the nocturnal inversion modified these values, causing large within night variability. These results indicate dET can generally be expected to show large spatial and temporal variability and to depend on the soil moisture state. For long periods between rain events, common in semi-arid environments, ET would be expected to impose negative forcing on the surface dv. The variability of D-excess in ET fluxes therefore needs to be considered when using dv to study moisture recycling and during extended dry periods may act as a tracer of the relative humidity of the oceanic moisture source. [ABSTRACT FROM AUTHOR]