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1. Multi‐GNSS Airborne Radio Occultation Observations as a Complement to Dropsondes in Atmospheric River Reconnaissance

   https://doi.org/10.1029/2021JD034865  

   Haase, J. S. ; Murphy, M. J. ; Cao, B. ; Ralph, F. M. ; Zheng, M. ; Delle Monache, L. ( November 2021 , Journal of Geophysical Research: Atmospheres)

   Variations in the water vapor that atmospheric rivers (ARs) carry toward North America within Pacific storms strongly modulates the spatiotemporal distribution of west‐coast precipitation. The “AR Recon” program was established to improve forecasts of landfalling Pacific‐coast ARs and their associated precipitation. Dropsondes are deployed from weather reconnaissance aircraft and pressure sensors have been added to drifting ocean buoys to fill a major gap in standard weather observations, while research is being conducted on the potential for airborne Global Navigation Satellite System (GNSS) radio occultation (ARO) to also contribute to forecast improvement. ARO further expands the spatial coverage of the data collected during AR Recon flights. This study provides the first description of these data, which provide water vapor and temperature information typically as far as 300 km to the side of the aircraft. The first refractivity profiles from European Galileo satellites are provided and their accuracy is evaluated using the dropsondes. It is shown that spatial variations in the refractivity anomaly (difference from the climatological background) are modulated by AR features, including the low‐level jet and tropopause fold, illustrating the potential for RO measurements to represent key AR characteristics. It is demonstrated that assimilation of ARO refractivity profiles can influencemore »the moisture used as initial conditions in a high‐resolution model. While the dropsonde measurements provide precise, in situ wind, temperature and water vapor vertical profiles beneath the aircraft, and the buoys provide surface pressure, ARO provides complementary thermodynamic information aloft in broad areas not otherwise sampled at no additional expendable cost.

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2. Evaluation of ambient ammonia measurements from a research aircraft using a closed-path QC-TILDAS operated with active continuous passivation

   https://doi.org/10.5194/amt-12-3717-2019  

   Pollack, Ilana B. ; Lindaas, Jakob ; Roscioli, J. Robert ; Agnese, Michael ; Permar, Wade ; Hu, Lu ; Fischer, Emily V. ( January 2019 , Atmospheric Measurement Techniques)

   Abstract. A closed-path quantum-cascade tunable infrared laserdirect absorption spectrometer (QC-TILDAS) was outfitted with an inertialinlet for filter-less separation of particles and several custom-designedcomponents including an aircraft inlet, a vibration isolation mountingplate, and a system for optionally adding active continuous passivation forgas-phase measurements of ammonia (NH3) from a research aircraft. Theinstrument was then deployed on the NSF/NCAR C-130 aircraft during researchflights and test flights associated with the Western wildfire Experiment forCloud chemistry, Aerosol absorption and Nitrogen (WE-CAN) field campaign.The instrument was configured to measure large, rapid gradients in gas-phaseNH3, over a range of altitudes, in smoke (e.g., ash and particles), inthe boundary layer (e.g., during turbulence and turns), in clouds, and in ahot aircraft cabin (e.g., average aircraft cabin temperatures expected toexceed 30 ∘C during summer deployments). Important designgoals were to minimize motion sensitivity, maintain a reasonable detectionlimit, and minimize NH3 “stickiness” on sampling surfaces to maintainfast time response in flight. The observations indicate that adding ahigh-frequency vibration to the laser objective in the QC-TILDAS andmounting the QC-TILDAS on a custom-designed vibration isolation plate weresuccessful in minimizing motion sensitivity of the instrument during flight.Allan variance analyses indicate that the in-flight precision of theinstrument is 60 ppt at 1 Hz corresponding to a 3σ detectionmore »limitof 180 ppt. Zero signals span ±200, or 400 pptv total, withcabin pressure and temperature and altitude in flight. The option for activecontinuous passivation of the sample flow path with1H,1H-perfluorooctylamine, a strong perfluorinated base, preventedadsorption of both water and basic species to instrument sampling surfaces.Characterization of the time response in flight and on the ground showedthat adding passivant to a “clean” instrument system had little impact onthe time response. In contrast, passivant addition greatly improved the timeresponse when sampling surfaces became contaminated prior to a test flight.The observations further show that passivant addition can be used tomaintain a rapid response for in situ NH3 measurements over the duration of anairborne field campaign (e.g., ∼2 months) since passivantaddition also helps to prevent future buildup of water and basic species oninstrument sampling surfaces. Therefore, we recommend the use of activecontinuous passivation with closed-path NH3 instruments when rapid(>1 Hz) collection of NH3 is important for the scientificobjective of a field campaign (e.g., sampling from aircraft or anothermobile research platform). Passivant addition can be useful for maintainingoptimum operation and data collection in NH3-rich and humid environments orwhen contamination of sampling surfaces is likely, yet frequent cleaning isnot possible. Passivant addition may not be necessary for fast operation,even in polluted environments, if sampling surfaces can be cleaned when thetime response has degraded.« less
3. Demonstration of a combined differential absorption and high spectral resolution lidar for profiling atmospheric temperature

   https://doi.org/10.1364/OE.379804  

   Stillwell, Robert A. ; Spuler, Scott M. ; Hayman, Matthew ; Repasky, Kevin S. ; Bunn, Catharine E. ( December 2019 , Optics Express)

   This work presents the first demonstration of atmospheric temperature measurement using the differential absorption lidar (DIAL) technique. While DIAL is routinely used to measure atmospheric gases such as ozone and water vapor, almost no success has been found in using DIAL to measure atmospheric temperature. Attempts to measure temperature using a well-mixed gas like oxygen (O₂) have largely failed based on a need for quantitative ancillary measurements of water vapor and atmospheric aerosols. Here, a lidar is described and demonstrated that simultaneously measuresO₂absorption, water vapor number density, and aerosol backscatter ratio. This combination of measurements allows for the first measurements of atmospheric temperature with useful accuracy. DIAL temperature measurements are presented to an altitude of 4kmwith 225mand 30minresolution with accuracy better than 3 K. DIAL temperature data is compared to a co-located Raman lidar system and radiosondes to evaluate the system’s performance. Finally, an analysis of current performance characteristics is presented, which highlights pathways for future improvement of this proof-of-concept instrument.
4. A Comparison of Convective Storm Inflow Moisture Variability between the Great Plains and the Southeastern United States Using Multiplatform Field Campaign Observations

   https://doi.org/10.1175/JTECH-D-22-0037.1  

   Lin, Guo ; Wang, Zhien ; Ziegler, Conrad ; Hu, Xiao-Ming ; Xue, Ming ; Geerts, Bart ; Chu, Yufei ( May 2023 , Journal of Atmospheric and Oceanic Technology)

   Abstract The magnitude of water vapor content within the near-storm inflow can either support or deter the storm’s upscale growth and maintenance. However, the heterogeneity of the moisture field near storms remains poorly understood because the operational observation network lacks detail. This observational study illustrates that near-storm inflow water vapor environments are both significantly heterogeneous and different than the far-inflow storm environment. This study also depicts the importance of temporal variation of water vapor mixing ratio (WVMR) to instability during the peak tornadic seasons in the U.S. Southeast and Great Plains regions during the Verification of the Origins of Rotation in Tornadoes Experiment Southeast 2018 (VSE18) campaign and the Targeted Observation by Radar and UAS of Supercells (TORUS) campaign, respectively. VSE18 results suggest that the surface processes control WVMR variation significantly in lower levels, with the highest WVMR mainly located near the surface in inflows in the southeast region. In contrast, TORUS results show more vertically homogeneous WVMR profiles and rather uniform water vapor distribution variation occurring in deep, moist stratified inflows in the Great Plains region. Temporal water vapor variations within 5-min periods could lead to over 1000 J kg −1 CAPE changes in both VSE18 and TORUS, whichmore »represent significant potential buoyancy perturbations for storms to intensify or decay. These temporal water vapor and instability evolutions of moving storms remain difficult to capture via radiosondes and fixed in situ or profiling instrumentation, yet may exert a strong impact on storm evolution. This study suggests that improving observations of the variability of near-storm inflow moisture can accurately refine a potential severe weather threat. Significance Statement It has long been recognized that better observations of the planetary boundary layer (PBL) inflow near convective storms are needed to improve severe weather forecasting. The current operational networks essentially do not provide profile measurements of the PBL, except for the sparsely spaced 12-hourly sounding network. More frequent geostationary satellite observations do not provide adequately high vertical resolution in the PBL. This study uses airborne lidar profiler measurements to examine moisture in the inflow region of convective storms in the Great Plains and the southeastern United States during their respective tornadic seasons. Rapid PBL water vapor variations on a ∼5 min time scale can lead to CAPE perturbations exceeding 1000 J kg −1 , representing significant perturbations that could promote storm intensification or decay. Severe thunderstorms may generate high-impact weather phenomena, such as tornadoes, high winds, hail, and heavy rainfall, which have substantial socioeconomic impacts. Ultimately, by contrasting characteristics of the convective storm inflow in the two regions, this study may lead to a more accurate assessment of severe weather threats.« less
5. Distinguishing Convective-Transition Moisture-Temperature Relationships with a Constellation of Polarimetric Radio Occultation Observations in and near Convection

   https://doi.org/10.3390/atmos13020259  

   Turk, F. Joseph ; Padullés, Ramon ; Morabito, David D. ; Emmenegger, Todd ; Neelin, J. David ( February 2022 , Atmosphere)

   Convective transition statistics serve as diagnostics for the parameterization of convection in climate and weather forecast models by characterizing the dependence of convection on the humidity-temperature environment. The observed strong pickup of precipitation as a function of layer-averaged water vapor and temperature is captured in models with varying accuracy. For independent observational verification, a low-Earth orbiting satellite constellation of Global Navigation Satellite System (GNSS) polarimetric radio occultation (PRO) measurements would be spaced such that adjacent RO would capture different profiles within and immediately adjacent to convection. Here, the number of profile observations needed to distinguish between convective transition relations by different tropospheric temperature ranges is determined, over different tropical oceanic basins. To obtain these, orbit simulations were performed by flying different satellite constellations over global precipitation from the Global Precipitation Measurement (GPM) mission, varying the numbers of satellites, orbit altitude, and inclination. A 45-degree orbit inclination was found to be a good tradeoff between maximizing the number of observations collected per day, and the desired 50–150-km spacing between individual RO ray paths. Assuming a set of reasonable assumptions for net data yield, three tropospheric temperatures can be distinguished by 1 K with a six-month on-orbit duration from a constellation ofmore »at least three satellites.« less