Mid-latitude Flights Research Articles

Constraints on the Optical Depth to Reionization from Balloon-borne Cosmic Microwave Background Measurements

We assess the uncertainty with which a balloon-borne experiment, nominally called Tau Surveyor (τS), can measure the optical depth to reionization σ(τ) with given realistic constraints of instrument noise and foreground emissions. Using a τS fiducial design with six frequency bands between 150 and 380 GHz, with white and uniform map noise of 7 μK arcmin, achievable with a single midlatitude flight, and including Planck's 30 and 44 GHz data, we assess the error σ(τ) obtained with three foreground models and as a function of sky fraction f sky between 40% and 54%. We carry out the analysis using both parametric and blind foreground separation techniques. We compare the σ(τ) values to those obtained with low-frequency and high-frequency versions of the experiment called τS-lf and τS-hf, which have only four and up to eight frequency bands with narrower and wider frequency coverage, respectively. We find that with τS, the lowest constraint is σ(τ) = 0.0034, obtained for one of the foreground models with f sky = 54%. σ(τ) is larger, in some cases by more than a factor of 2, for smaller sky fractions, with τS-lf, or as a function of foreground model. The τS-hf configuration does not lead to significantly tighter constraints. The exclusion of the 30 and 44 GHz data, which give information about synchrotron emission, leads to significant τ misestimates. Decreasing noise by an ambitious factor of 10, while keeping f sky = 40%, gives σ(τ) = 0.0031. The combination of σ(τ) = 0.0034, baryon acoustic oscillation data from DESI, and future cosmic microwave background B-mode lensing data from the CMB-S3/CMB-S4 experiments could give σ(∑m ν ) = 17 meV.

Flight safety implications of the extreme solar proton event of 23 February 1956

There is considerable speculation about the effects at aircraft altitudes resulting from extreme solar proton events. The ground level event (GLE) of 23 February 1956 (GLE 5), remains the largest solar proton event of the neutron monitor era in terms of its influence on count rates at monitors near sea level. During this GLE the count rate was increased by as much as 4760% (15-min average) at the Leeds monitor relative to the count rate from galactic cosmic radiation (GCR). Two modern models of the event cumulative solar proton spectrum for this event, a 6-parameter fit in energy and a 4-parameter Band fit in rigidity, are compared with 1-h of GCR at solar minimum. While effective doses calculated with CARI-7A for both models at low geomagnetic cutoff rigidities are indeed high when compared with GCR and can exceed recommended exposure limits, both GLE spectra exhibit a much stronger dependence on cutoff rigidity than GCR, and a larger fraction of the dose from neutrons. At locations with cutoff rigidities above 4.2 and 6.4 GV, respectively, the GLE effective doses are smaller than the GCR hourly dose. At locations with cutoff rigidities above about 4 GV, GCR was the dominant source of exposure in 10 h or less at all altitudes examined. This suggests that if a similar event occurs in the future, low- and mid-latitude flights at modern jet flight altitudes could be well-protected by Earth’s magnetic field.

Measuring Reionization, Neutrino Mass, and Cosmic Inflation with BFORE

BFORE is a NASA high-altitude ultra-long-duration balloon mission proposed to measure the cosmic microwave background (CMB) across half the sky during a 28-day mid-latitude flight launched from Wanaka, New Zealand. With the unique access to large angular scales and high frequencies provided by the balloon platform, BFORE will significantly improve measurements of the optical depth to reionization tau, breaking parameter degeneracies needed for a measurement of neutrino mass with the CMB. The large angular scale data will enable BFORE to hunt for the large-scale gravitational wave B-mode signal, as well as the degree-scale signal, each at the r~0.01 level. The balloon platform allows BFORE to map Galactic dust foregrounds at frequencies where they dominate, in order to robustly separate them from CMB signals measured by BFORE, in addition to complementing data from ground-based telescopes. The combination of frequencies will also lead to velocity measurements for thousands of galaxy clusters, as well as probing how star-forming galaxies populate dark matter halos. The mission will be the first near-space use of TES multichroic detectors (150/217 GHz and 280/353 GHz bands) using highly-multiplexed mSQUID microwave readout, raising the technical readiness level of both technologies.

Aviation effects on already-existing cirrus clouds.

Determining the effects of the formation of contrails within natural cirrus clouds has proven to be challenging. Quantifying any such effects is necessary if we are to properly account for the influence of aviation on climate. Here we quantify the effect of aircraft on the optical thickness of already-existing cirrus clouds by matching actual aircraft flight tracks to satellite lidar measurements. We show that there is a systematic, statistically significant increase in normalized cirrus cloud optical thickness inside mid-latitude flight tracks compared with adjacent areas immediately outside the tracks.

Single‐particle measurements of midlatitude black carbon and light‐scattering aerosols from the boundary layer to the lower stratosphere

A single‐particle soot photometer (SP2) was flown on a NASA WB‐57F high‐altitude research aircraft in November 2004 from Houston, Texas. The SP2 uses laser‐induced incandescence to detect individual black carbon (BC) particles in an air sample in the mass range of ∼3–300 fg (∼0.15–0.7 μm volume equivalent diameter). Scattered light is used to size the remaining non‐BC aerosols in the range of ∼0.17–0.7 μm diameter. We present profiles of both aerosol types from the boundary layer to the lower stratosphere from two midlatitude flights. Results for total aerosol amounts in the size range detected by the SP2 are in good agreement with typical particle spectrometer measurements in the same region. All ambient incandescing particles were identified as BC because their incandescence properties matched those of laboratory‐generated BC aerosol. Approximately 40% of these BC particles showed evidence of internal mixing (e.g., coating). Throughout profiles between 5 and 18.7 km, BC particles were less than a few percent of total aerosol number, and black carbon aerosol (BCA) mass mixing ratio showed a constant gradient with altitude above 5 km. SP2 data was compared to results from the ECHAM4/MADE and LmDzT‐INCA global aerosol models. The comparison will help resolve the important systematic differences in model aerosol processes that determine BCA loadings. Further intercomparisons of models and measurements as presented here will improve the accuracy of the radiative forcing contribution from BCA.

The applicability of model based aircraft radiation dose estimates

The monthly cosmic radiation modulation parameters provided to compute radiation dose on aircraft flights do not account for short-term temporal variations such as Forbush decreases or high-speed solar wind flows. The currently available radiation dose models also do not account for changes in geomagnetic conditions when the geomagnetic cutoff may be significantly lower than the average predicted by use of the international geomagnetic reference field models. We utilize on-board aircraft radiation dosimeter data acquired during the major solar-terrestrial disturbances of October/November 2003 to demonstrate these effects along with the increased dose due to the ground-level event of 29 October 2003 on a mid-latitude flight path.

Transport into the northern hemisphere lowermost stratosphere revealed by in situ tracer measurements

The Lightweight Airborne Chromatograph Experiment (LACE) has made in situ measurements of several long‐lived trace gases in the upper troposphere and lower to middle stratosphere as part of the Observations of the Middle Stratosphere (OMS) balloon program. The tracers measured by LACE include several photolytic species (CFC‐11, CFC‐12, and halon‐1211) as well as SF6. LACE measurements of these long‐lived tracers as well as nearly simultaneous measurements of water vapor and CO2 are used to investigate transport into the lowermost stratosphere, a region where few in situ measurements exist. The measured photolytic species and water vapor are used in a simple mass balance calculation to estimate the mixture of tropospheric and overworld (θ>380 K) air in the lowermost stratosphere. In the northern midlatitudes during September 1996, most of the air in the lowermost stratosphere sampled at the flight location (34.5°N) was transported quasi‐isentropically from the troposphere. Measurements from both a May 1998 midlatitude flight and a June 1997 high‐latitude flight (64.5°N) revealed the air sampled in the lowermost stratosphere to be dominated by downward advection from the overworld. Atmospheric SF6 and CO2 can uniquely reveal timescales and spatial scales of transport due to these species' large growth rates and subsequent latitudinal surface and free tropospheric gradients. Measurements in the lowermost stratosphere from the September northern midlatitude flight coupled with surface measurements of these species revealed a transport timescale of no more than 1.5 months from the surface to the lowermost stratosphere. The SF6 and CO2 mixing ratios were also consistent with mostly Northern Hemisphere tropospheric air in the lowermost stratosphere. These results point out the usefulness of high‐resolution in situ measurements of long‐lived tracers to help determine timescales and spatial scales of transport in the region of the upper troposphere and lowermost stratosphere.

Space shuttle data and atmospheric models

Atmospheric density data obtained during the reentry of 22 Shuttle flights have been analyzed and compared with models. It was found that the density values from two flights that reentered through high latitudes were quite different from the values obtained from low and mid latitude flights. Data from a December high latitude flight agreed with models, although as low as 60% of the U.S. Standard Atmosphere, but the data from an October flight were as much as 25% below the October models, although 57% of the U.S. Standard. The difference was possibly due to the effects of particle precipitation. Data from the mid and low latitude flights, in general, agreed well with the models, with a mean deviation of −2.3% at 50km and −11% at 85km. The maximum variability at these altitudes was 8% and 22%, respectively. Most flights showed evidence of gravity waves above 70km, with largest amplitudes in summer, and little activity in the winter or at high latitudes. Data from three flights that reentered at a constant latitude of 27°N are close to the models near 50km, but are generally lower at higher altitudes and exhibit major variability above 70km, probably due to storm and convective activity. The results from three high inclination flights that reentered over the southern tropics agree with the models at 50km altitude, but at higher altitudes all the data are below the models. The conclusion is that the models for latitudes between 20°N and 20°S need to be revised.

The measurement of atomic oxygen in the mesosphere and lower thermosphere

A discussion of the laboratory calibration, calibration simulation, and accuracy of a resonance fluorescence instrument for measuring oxygen atoms is given. The discussion demonstrates that a sensor can be calibrated with good accuracy to obtain in situ measurements of the oxygen density in the mesosphere/lower thermosphere. Oxygen data are reported from six rocket flights. These data represent four midlatitude flights and two auroral flights. There are two night and two day profiles for the midlatitude experiments. The maximum densities found from these sets of data in the 90–100 km regions are between 1.5 × 10 11 cm −3 and 3.5 × 10 11 cm −3. Agreement with the MSIS-86 model predictions is obtained for altitudes above 120 km for midlatitude flights. The auroral data are less than the model prediction by about a factor of 2. The data show structure that is probably indicative of gravity wave effects of a nominal 5 km vertical wavelength.