Quantitative relation between PMSE and ice mass density

Radar reflectivities associated with Polar Mesosphere Summer Echoes (PMSE) are compared with measurements of ice mass density in the mesopause region. The 54.5 MHz radar Moveable Atmospheric Radar for Antarctica (MARA), located at the Wasa/Aboa station in Antarctica (73° S, 13° W) provided PMSE measurements in December 2007 and January 2008. Ice mass density was measured by the Solar Occultation for Ice Experiment (SOFIE). The radar operated continuously during this period but only measurements close to local midnight are used for comparison, to coincide with the local time of the measurements of ice mass density. The radar location is at high geographic latitude but low geomagnetic latitude (61°) and the measurements were made during a period of very low solar activity. As a result, background electron densities can be modelled based on solar illumination alone. We find a close correlation between the time and height variations of radar reflectivity and ice mass density, at all PMSE heights, from 80 km up to 95 km. A quantitative expression relating radar reflectivities to ice mass density is found, including an empirical dependence on background electron density. Using this relation, we can use PMSE reflectivities as a proxy for ice mass density, and estimate the daily variation of ice mass density from the daily variation of PMSE reflectivities. According to this proxy, ice mass density is maximum around 05:00–07:00 LT, with lower values around local noon, in the afternoon and in the evening. This is consistent with the small number of previously published measurements and model predictions of the daily variation of noctilucent (mesospheric) clouds and in contrast to the daily variation of PMSE, which has a broad daytime maximum, extending from 05:00 LT to 15:00 LT, and an evening-midnight minimum

Observations of aerosol by the HALOE Experiment onboard UARS: A preliminary validation

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94744/1/grl6692.pd

HALOE Algorithm Improvements for Upper Tropospheric Sounding

This report details the ongoing efforts by GATS, Inc., in conjunction with Hampton University and University of Wyoming, in NASA's Mission to Planet Earth UARS Science Investigator Program entitled "HALOE Algorithm Improvements for Upper Tropospheric Soundings." The goal of this effort is to develop and implement major inversion and processing improvements that will extend HALOE measurements further into the troposphere. In particular, O3, H2O, and CH4 retrievals may be extended into the middle troposphere, and NO, HCl and possibly HF into the upper troposphere. Key areas of research being carried out to accomplish this include: pointing/tracking analysis; cloud identification and modeling; simultaneous multichannel retrieval capability; forward model improvements; high vertical-resolution gas filter channel retrievals; a refined temperature retrieval; robust error analyses; long-term trend reliability studies; and data validation. The current (first-year) effort concentrates on the pointer/tracker correction algorithms, cloud filtering and validation, and multi-channel retrieval development. However, these areas are all highly coupled, so progress in one area benefits from and sometimes depends on work in others

Persistence of upper stratospheric wintertime tracer variability into the Arctic spring and summer

Using data from the Aeronomy of Ice in the Mesosphere (AIM) and Aura satellites, we have categorized the interannual variability of winter- and springtime upper stratospheric methane (CH4). We further show the effects of this variability on the chemistry of the upper stratosphere throughout the following summer. Years with strong wintertime mesospheric descent followed by dynamically quiet springs, such as 2009, lead to the lowest summertime CH4. Years with relatively weak wintertime descent, but strong springtime planetary wave activity, such as 2011, have the highest summertime CH4. By sampling the Aura Microwave Limb Sounder (MLS) according to the occultation pattern of the AIM Solar Occultation for Ice Experiment (SOFIE), we show that summertime upper stratospheric chlorine monoxide (ClO) almost perfectly anticorrelates with the CH4. This is consistent with the reaction of atomic chlorine with CH4 to form the reservoir species, hydrochloric acid (HCl). The summertime ClO for years with strong, uninterrupted mesospheric descent is about 50 % greater than in years with strong horizontal transport and mixing of high CH4 air from lower latitudes. Small, but persistent effects on ozone are also seen such that between 1 and 2 hPa, ozone is about 4–5 % higher in summer for the years with the highest CH4 relative to the lowest. This is consistent with the role of the chlorine catalytic cycle on ozone. These dependencies may offer a means to monitor dynamical effects on the high-latitude upper stratosphere using summertime ClO measurements as a proxy. Additionally, these chlorine-controlled ozone decreases, which are seen to maximize after years with strong uninterrupted wintertime descent, represent a new mechanism by which mesospheric descent can affect polar ozone. Finally, given that the effects on ozone appear to persist much of the rest of the year, the consideration of winter/spring dynamical variability may also be relevant in studies of ozone trends

Version 1.3 AIM SOFIE Measured Methane (CH4): Validation and Seasonal Climatology

The V1.3 methane (CH4) measured by the Aeronomy of Ice in the Mesosphere (AIM) Solar Occultation for Ice Experiment (SOFIE) instrument is validated in the vertical range of ~25–70 km. The random error for SOFIE CH4 is ~0.1–1% up to ~50 km and degrades to ~9% at ∼ 70 km. The systematic error remains at ~4% throughout the stratosphere and lower mesosphere. Comparisons with CH4 data taken by the SCISAT Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) and the Envisat Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) show an agreement within ~15% in the altitude range ~30–60 km. Below ~25 km SOFIE CH4 is systematically higher (≥20%), while above ~65 km it is lower by a similar percentage. The sign change from the positive to negative bias occurs between ~55 km and ~60 km (or ~40 km and ~45 km) in the Northern (or Southern) Hemisphere. Methane, H2O, and 2CH4 + H2O yearly differences from their values in 2009 are examined using SOFIE and MIPAS CH4 and the Aura Microwave Limb Sounder (MLS) measured H2O. It is concluded that 2CH4 + H2O is conserved with altitude up to an upper limit between ~35 km and ~50 km depending on the season. In summer this altitude is higher. In the Northern Hemisphere the difference relative to 2009 is the largest in late spring and the established difference prevails throughout summer and fall, suggesting that summer and fall are dynamically quiet. In both hemispheres during winter there are disturbances (with a period of ~1 month) that travel downward throughout the stratosphere with a speed similar to the winter descent. ©2016. American Geophysical Union

On the relative roles of dynamics and chemistry governing the abundance and diurnal variation of low latitude thermospheric nitric oxide

We use data from two NASA satellites, the Thermosphere Ionosphere Energetics and Dynamics (TIMED) and the Aeronomy of Ice in the Mesosphere (AIM) satellites in conjunction with model simulations from the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM) to elucidate the key dynamical and chemical factors governing the abundance and diurnal variation of nitric oxide (NO) at near solar minimum conditions and low latitudes. This analysis was enabled by the recent orbital precession of the AIM satellite which caused the solar occultation pattern measured by the Solar Occultation for Ice Experiment (SOFIE) to migrate down to low and mid latitudes for specific periods of time. We use a month of NO data collected in January 2017 to compare with two versions of the TIME-GCM, one driven solely by climatological tides and analysis-derived planetary waves at the lower boundary and free running at all other altitudes, while the other is constrained by a high-altitude analysis from the Navy Global Environmental Model (NAVGEM)up to the mesopause. We also compare SOFIE data with a NO climatology from the Nitric Oxide Empirical Model (NOEM). Both SOFIE and NOEM yield peak NO abundances of around 4×107cm−3; however, the SOFIE profile peaks about 6-8 km lower than NOEM. We show that this difference is likely a local time effect; SOFIE being a dawn measurement and NOEM representing late morning/near noon. The constrained version of TIME-GCM exhibits a low altitude dawn peak while the model that is forced solely at the lower boundary and free running above does not. We attribute this difference due to a phase change in the semi-diurnal tide in the NAVGEM-constrained model causing descent of high NO mixing ratio air near dawn. This phase difference between the two models arises due to differences in the mesospheric zonal mean zonal winds. Regarding the absolute NO abundance, all versions of the TIME-GCM overestimate this. Tuning the model to yield calculated atomic oxygen in agreement with TIMED data helps, but is insufficient. Further, the TIME-GCM underestimates the electron density [e-] as compared with the International Reference Ionosphere empirical model. This suggests a potential conflict with the requirements of NO modeling and [e-] modeling since one solution typically used to increase model [e-] is to increase the solar soft X ray flux which would, in this case, worsen the NO model/data discrepancy

NRLMSIS 2.1: An Empirical Model of Nitric Oxide Incorporated Into MSIS

We have developed an empirical model of nitric oxide (NO) number density at altitudes from similar to 73 km to the exobase, as a function of altitude, latitude, day of year, solar zenith angle, solar activity, and geomagnetic activity. The model is part of the NRLMSIS (R) 2.1 empirical model of atmospheric temperature and species densities; this upgrade to NRLMSIS 2.0 consists solely of the addition of NO. MSIS 2.1 assimilates observations from six space-based instruments: UARS/HALOE, SNOE, Envisat/MIPAS, ACE/FTS, Odin/SMR, and AIM/SOFIE. We additionally evaluated the new model against independent extant NO data sets. In this paper, we describe the formulation and fitting of the model, examine biases between the data sets and model and among the data sets, compare with another empirical NO model (NOEM), and discuss scientific aspects of our analysis