Remote detection of OH

This is a remote measurement technique utilizing a XeCl excimer laser tuned to the Q sub 21 1 rotational transition of the 0-0, A-X band at 307.847 nm. A wavemeter is under development to monitor, on a pulse-to-pulse basis, both the laser lineshape and absolute wavelength. Fluorescence is detected with a multiple Fabry-Perot type filter with a spectral resolution on the order of 0.001 nm. This is tuned to the overlapping Q sub 2 2, Q sub 12 2, Q sub 2 3, and Q sub 12 3 rotational transitions at 308.986 nm. The fringe pattern from this filter is imaged using a discrete, multi-anode detector which has a photon gain of 10 to the 8th power. This permits the simultaneous monitoring of OH fluorescence, N2 and/or O2 rotational Raman scattering and broadband background levels. The use of three etalons in series provides sufficient rejection, approx. greater than 10 to the 10th power, against the laser radiation only 1.2 nm away

NDSC and JPL stratospheric lidars

The Network for the Detection of Stratospheric Change is an international cooperation providing a set of high-quality, remote-sensing instruments at observing stations around the globe. A brief description of the NDSC and its goals is presented. Lidar has been selected as the NDSC instrument for measurements of stratospheric profiles of ozone, temperature, and aerosol. The Jet Propulsion Laboratory has developed and implemented two stratospheric lidar systems for NDSC. These are located at Table Mountain, California, and at Mauna Loa, Hawaii. These systems, which utilize differential absorption lidar, Rayleigh lidar, raman lidar, and backscatter lidar, to measure ozone, temperature, and aerosol profiles in the stratosphere are briefly described. Examples of results obtained for both long-term and individual profiles are presented

Surface ozone levels at Table Mountain during STOIC 1989

As a part of the routine operations of the Jet Propulsion Laboratory atmospheric measurements program at the Table Mountain Facility, the surface ozone concentration is continuously monitored using a Dasibi photometer. The influence of the Los Angeles basin to the southwest of the facility and the height of the inversion layer cause large fluctuations in the ozone concentration. Peaks as high as 200 parts per billion by volume (ppbv) were observed during the Stratospheric Ozone Intercomparison Campaign (STOIC) compared to a normal background level near 50 ppbv. These measurements, made during STOIC, were important in assessing the impact of the surface ozone concentration on the various instruments participating in the campaign

Lidar measurements of stratospheric ozone at Table Mountain, California, since 1988

Regular measurements of stratospheric ozone concentration profiles have been made at Table Mountain, California, since January 1988. During the period to December 1991, 435 independent profiles were measured by the differential absorption lidar technique. These long-term results, and an evaluation of their quality, is presented in this paper

Lidar Validation Measurements at the NOAA Mauna Loa Observatory NDACC Station

NASA's Goddard Space Flight Center (GSFC) transported two lidar instruments to the NOAA facility at the Mauna Loa Observatory (MLO) on the Big Island of Hawaii, to participate in an official, extended validation campaign. This site is situated 11,141 ft. above sea level on the side of the mountain. The observatory has been making atmospheric measurements regularly since the 1950's, and has hosted the GSFC Stratospheric Ozone (STROZ) Lidar and the GSFC Aerosol and Temperature (AT) Lidar on several occasions, most recently between November, 2012 and November, 2015. The purpose of this extended deployment was to participate in Network for the Detection of Atmospheric Composition Change (NDACC) Validation campaigns with the JPL Stratospheric Ozone Lidar and the NOAA Temperature, Aerosol and Water Vapor instruments as part of the routine NDACC Validation Protocol

Airborne and Ground-Based Measurements Using a High-Performance Raman Lidar

The same RASL hardware as described in part I was installed in a ground-based mobile trailer and used in a water vapor lidar intercomparison campaign, hosted at Table Mountain, CA, under the auspices of the Network for the Detection of Atmospheric Composition Change (NDACC). The converted RASL hardware demonstrated high sensitivity to lower stratospheric water vapor indicating that profiling water vapor at those altitudes with sufficient accuracy to monitor climate change is possible. The measurements from Table Mountain also were used to explain the reason, and correct , for sub-optimal airborne aerosol extinction performance during the flight campaign

A search for supernova-like optical counterparts to ASKAP-localised Fast Radio Bursts

Fast radio bursts (FRBs) are millisecond-scale radio pulses, which originate in distant galaxies and are produced by unknown sources. The mystery remains partially because of the typical difficulty in localising FRBs to host galaxies. Accurate localisations delivered by the Commensal Real-time ASKAP Fast Transients (CRAFT) survey now provide an opportunity to study the host galaxies and potential transient counterparts of FRBs at a large range of wavelengths. In this work, we investigate whether the first three FRBs accurately localised by CRAFT have supernova-like transient counterparts. We obtained two sets of imaging epochs with the Very Large Telescope for three host galaxies, one soon after the burst detection and one several months later. After subtracting these images no optical counterparts were identified in the associated FRB host galaxies, so we instead place limits on the brightness of any potential optical transients. A Monte Carlo approach, in which supernova light curves were modelled and their base properties randomised, was used to estimate the probability of a supernova associated with each FRB going undetected. We conclude that Type Ia and IIn supernovae are unlikely to accompany every apparently non-repeating FRB.Comment: 7 pages, 3 figures. Accepted to Astronomy & Astrophysics on 03 June 202

The unseen host galaxy and high dispersion measure of a precisely-localised Fast Radio Burst suggests a high-redshift origin

FRB 20210912A is a fast radio burst (FRB), detected and localised to sub-arcsecond precision by the Australian Square Kilometre Array Pathfinder. No host galaxy has been identified for this burst despite the high precision of its localisation and deep optical and infrared follow-up, to 5-$\sigma$ limits of $R=26.7$ mag and $K_\mathrm{s}=24.9$ mag with the Very Large Telescope. The combination of precise radio localisation and deep optical imaging has almost always resulted in the secure identification of a host galaxy, and this is the first case in which the line-of-sight is not obscured by the Galactic disk. The dispersion measure of this burst, $\mathrm{DM_{FRB}}=1233.696\pm0.006~\mathrm{pc}\ \mathrm{cm}^{-3}$, allows for a large source redshift of $z>1$ according to the Macquart relation. It could thus be that the host galaxy is consistent with the known population of FRB hosts, but is too distant to detect in our observations ($z>0.7$ for a host like that of the first repeating FRB source, FRB 20121102A); that it is more nearby with a significant excess in $\mathrm{DM_{host}}$, and thus dimmer than any known FRB host; or, least likely, that the FRB is truly hostless. We consider each possibility, making use of the population of known FRB hosts to frame each scenario. The fact of the missing host has ramifications for the FRB field: even with high-precision localisation and deep follow-up, some FRB hosts may be difficult to detect, with more distant hosts being the less likely to be found. This has implications for FRB cosmology, in which high-redshift detections are valuable.Comment: 14 pages, 6 figures. Revised based on referee's comments and accepted to MNRA

VALIDATION OF GOMOS OZONE PROFILES USING NDSC LIDAR : STATISTICAL COMPARISONS

ABSTRACT The lidars deployed in the NDSC framework have been used for the validation of GOMOS onboard ENVISAT. During the commissioning phase around ten coincidences per site have been investigated. No significant bias, larger than ±5 %, has been reported except around 50 km and 20 km where both techniques are known to present some limitations. The estimated errors of both GOMOS and lidar are in good agreement with the standard deviation of the differences between coincidences. At higher latitude, comparisons are not so good because of the measurement conditions of bright limb during this period

A study of ozone variability and its connection with meridional transport in the northern Pacific lower stratosphere during summer 2002

International audienceA preliminary study of the impact of the north-central Pacific circulation in the subtropical stratosphere on ozone variability locally observed by lidar is presented. The results from the upper tropospheric and stratospheric ozone measurements of the Jet Propulsion Laboratory lidars located at Mauna Loa Observatory (MLO), Hawaii, and Table Mountain Facility (TMF), California, during summer 2002 were compared to isentropic potential vorticity (IPV) advected on 54 levels from 320 to 1500 K by the high-resolution model MIMOSA. The correlation between ozone measured by lidar, and the origin of the 10-day backward trajectories of the air parcels sampled, was also investigated. Near the tropopause, strong positive correlation between ozone mixing ratio and IPV was observed at both MLO and TMF lidar sites. The largest fluctuations were centered near 350 K and are associated with the meridional displacement of the tropopause by Rossby waves north or south of the observing sites. These large displacements were occasionally accompanied by Rossby wave breaking (RWB), as was identified several times during the summer in the vicinity of the Hawaiian Islands. Using IPV maps, a case study of the 13 July event is briefly presented. This event appears to be typical of breaking events previously investigated at midlatitudes, including the southward intrusion of high-PV air originating in the high-latitude lower stratosphere. This time the intrusion was observed to extend deep in the subtropics. Strong positive ozone anomalies were simultaneously measured by the MLO lidar. Positive correlation between ozone and the equivalent latitude averaged along the parcels' trajectories was seen up to 475 K in the stratosphere. At and above 750 K, negative correlation was calculated for both TMF and MLO. For TMF the altitude dependence of the correlation is similar to that already observed for summer and winter midlatitudes For MLO the observed negative correlation was found to be the result of opposite seasonal and interannual tendencies in ozone and equivalent latitude throughout the summer. All other correlations are associated with a higher intraseasonal variability of both ozone and the parcels' origin, as compared to their seasonal tendencies