Mesospheric Temperature Mapper Research Articles

Investigation of a “wall” wave event

A bright airglow event was observed at Maui, Hawaii, on the night of 11–12 August 2004 with multiple instruments including a Na wind/temperature lidar, an airglow imager, and a mesospheric temperature mapper. The characteristics of this event were investigated with measurements from these instruments. Analysis showed that this event was caused by a large‐amplitude, upward‐propagating gravity wave with a period of about 4–5 hours and a vertical wavelength of about 20 km, i.e., a “wall” wave. This wall wave induced dramatic changes in temperature (60 K), airglow intensity (doubled in the OH and tripled in the O2 emissions), and Na abundance (tripled). It experienced strong dissipation and induced large downward heat flux with values about an order of magnitude larger than the annual mean. The wave also carried large momentum flux (∼70 m2 s−2).

Terdiurnal wave signatures in the upper mesospheric temperature and their association with the wind fields at low latitudes (20°N)

A novel investigation of terdiurnal (8‐hour) oscillations in the mesosphere and lower‐thermosphere temperature and wind field over Maui, Hawaii (20.8°N, 156.2°W) has been performed. Coincident observations using a mesospheric temperature mapper and a meteor wind radar were obtained since May 2002 as part of the Maui Mesosphere and Lower Thermosphere (Maui MALT) program to investigate the seasonal structure and dynamics of the low‐latitude middle atmosphere. This study focuses on a 10‐day period in July 2002 when a persistent ∼8‐hour oscillation was identified in dual measurements of the OH (6,2) and O2 (0,1) nocturnal rotational temperatures sampled at nominal altitudes of 87 and 94 km, respectively. During the summer months, the semidiurnal and diurnal tidal temperature components are expected to be minimal, and these data are most suitable for investigating the terdiurnal wave component, which is usually much weaker. Our results show that the primary 8‐hour oscillation observed during this 10‐day period exhibited a mean amplitude ∼5.5 K and a well‐defined phase shift (∼1‐hour) between the OH and O2 temperatures (with the O2 oscillation always leading). The downward phase progression and inferred mean vertical wavelength of ∼63 km are most consistent with that expected for the terdiurnal tide. Coincident meteor radar measurements also show an intermittent 8‐hour periodicity in the wind data. In particular, a detailed comparison of the winds and temperatures over a 4‐day interval within this period suggests a significant correlation indicating a near in‐phase temperature relation with the meridional wind component and a near‐antiphase relation with the zonal wind component. Comparison of the OH and O2 8‐hour temperature amplitudes also shows strong evidence for highly variable wave dissipation, with amplitude growth factors ranging from 0.6 to 1.9 throughout this period.

Comparison of simultaneous Na lidar and mesospheric nightglow temperature measurements and the effects of tides on the emission layer heights

A detailed comparative study of two new mesospheric temperature data sets, measured by different remote‐sensing techniques, has been performed as part of a long‐term investigation of low‐latitude mesospheric dynamics. Coincident observations using the University of Illinois Na wind/temperature lidar and the Utah State University CEDAR Mesospheric Temperature Mapper (MTM) were conducted from the summit of Haleakala Crater, Maui, Hawaii (20.8°N, 156.2°W, ∼3000 m) as part of the Maui‐MALT program. High‐quality joint measurements were obtained during four lidar campaign periods, and 16 nights of data, spanning the interval January 2002 to October 2003, are presented here as example observations during each season. The Na lidar was coupled to the Air Force 3.7 m diameter steerable telescope providing exceptional quality temperature (and wind) data spanning the altitude range ∼80–105 km. At the same time the MTM sequentially sampled the NIR OH (6,2) Meinel band and the O2 (0,1) Atmospheric band nightglow emissions to determine the height‐weighted mesospheric temperature at two nominal altitudes within this region. Comparison of these two nocturnal data sets shows exceptionally good agreement on a point‐to‐point, as well as a nightly mean basis, especially when allowances were made for physically reasonable changes in height during the course of the night for each of the nightglow layers. This analysis yields mean nocturnal altitudes of 88.6 km with a nocturnal variability of ±3.0 km for the OH M (6,2) band emission layer and 94.4 km for the O2 (0,1) Atmospheric band mean altitude with a nocturnal variability of ±4.2 km. These results are in excellent accord with previous rocket, satellite and ground‐based observations and further establish the validity of these two complementary measurement techniques. Furthermore, analysis of the computed height changes inferred from this study indicates a systematic decrease in altitude of both emission layers by up to several kilometers, whenever the lidar data showed evidence of strong diurnal or semidiurnal tidal forcing. The apparent downward trend in altitude was found to track the phase of the prevailing tidal motion providing new evidence for the effects of tides (or long‐period gravity waves) on the height variability of the nightglow layers.

Characterization of the semi-annual-oscillation in mesospheric temperatures at low-latitudes

Abstract Novel measurements of the seasonal variability in mesospheric temperature at low-latitudes have been obtained from Maui, Hawaii (20.8°N, 156.2°W) during a 25-month period from October 2001 to January 2004. Independent observations of the OH (6, 2) Meinel band (peak height ∼87 km) and the O2 (0–1) atmospheric band emission (∼94 km) were made using the CEDAR Mesospheric Temperature Mapper. The data revealed a coherent oscillation in emission intensity and rotational temperature with a well-defined periodicity of 181 ± 7 days. The amplitude of this oscillation was determined to be ∼5–6 K in temperature and ∼8–9% in intensity for both the OH and O2 data sets. In addition, a strong asymmetry in the shape of the oscillation was also observed with the spring maximum significantly larger than the fall peak. These data provide new evidence in support of a semi-annual-oscillation in mesospheric temperature (and airglow emission intensities) and help quantify its seasonal characteristics.

First near‐global retrievals of OH rotational temperatures from satellite‐based Meinel band emission measurements

For the first time near‐global retrievals of mesopause OH rotational temperatures from satellite‐borne Meinel band emission measurements are presented. The measurements of the OH (3‐1) Meinel band near 1.5 micron were performed with the SCIAMACHY instrument on the European Space Agency's environmental satellite Envisat. The derived OH (3‐1) rotational temperatures are shown to be in reasonable agreement with the CIRA (1986) atmosphere temperatures for the seasons and latitudes considered. The derived temperatures are in good agreement with ground‐based measurements of the OH rotational temperature performed with a CEDAR Mesospheric Temperature Mapper (MTM) at Maui, Hawaii (21°N/204°E), with the GRound based Infrared P‐branch Spectrometer I (GRIPS‐I) at Hohenpeißenberg (47°N/11°E) and with GRIPS‐II at Wuppertal (51°N/7°E). The SCIAMACHY limb nighttime observations provide a unique data set of near‐global OH rotational temperature to study seasonal and geographical variations, dynamical processes and possibly long‐term temperature trends, if an extended data set becomes available in the future.

Effects of a large mesospheric temperature enhancement on the hydroxyl rotational temperature as observed from the ground

The rotational temperature obtained from the rotational population distribution in the bands of the hydroxyl airglow has been shown to be a suitable proxy for the temperature at a height of 87 km [She and Lowe, 1998]. In this paper we examine in detail simultaneous observations on November 2–3, 1997, at Fort Collins, Colorado (41°N, 105°W), with both a sodium temperature lidar and the Coupling, Energetics, and Dynamics of Atmospheric Regions (CEDAR) OH mesospheric temperature mapper during which significant differences between the hydroxyl and lidar temperatures occur. The large differences are associated with a major temperature enhancement in the region of the peak of the hydroxyl emission. We model the effect on the shape of the emission rate profile of the hydroxyl airglow caused by the large temperature enhancement observed on this night by the lidar. As a result of the temperature sensitivity of the processes that give rise to the airglow, the profile shows major distortions from its normal shape. These distortions in turn lead to hydroxyl rotational temperatures that differ significantly from the 87‐km lidar observations. The mean rotational temperature deduced in this way agrees well with the observed values. Such deviations in the temperature are expected to be rare, occurring only when a large temperature enhancement occurs near the peak of the airglow emission profile.

Large amplitude perturbations in mesospheric OH Meinel and 87‐Km Na lidar temperatures around the autumnal equinox

Two high‐precision CEDAR instruments, an OH Mesospheric Temperature Mapper (MTM) and a Na Temperature Lidar, have been used to investigate seasonal variability in the mid‐latitude temperature at ∼87 km altitude over the western USA. Here we report the observation of a large perturbation in mesospheric temperature that occurs shortly after the autumnal equinox in close association with the penetration of planetary‐wave energy from the troposphere into the mesosphere. This perturbation has been observed on three occasions and exhibits a departure of up to ∼25–30 K from the nominal seasonal trend during a disturbed period of ∼2 weeks. Such behavior represents a dramatic transient departure from the seasonal trend expected on the basis of current empirical models. These novel results coupled with a recent TIME‐GCM modeling study [Liu et al., 2000] provide important insight into the role of planetary waves in mesospheric variability during the equinox periods.

Comparison of terdiurnal tidal oscillations in mesospheric OH rotational temperature and Na lidar temperature measurements at mid-latitudes for fall/spring conditions

Results from two different instrumental techniques, an Na Wind/Temperature Lidar and an OH Mesospheric Temperature Mapper, have been combined to investigate the occurrence and properties of the mid-latitude terdiurnal (8-hr) tide at near mesopause altitudes (80–105 km). High-resolution Na lidar measurements were taken throughout the diurnal and annual cycle (1996–98) at Urbana, Illinois (40°N, 88°W) to characterize the seasonal behavior of the 24, 12, 8 and 6-hr tides. Complementary measurements using a recently developed CCD imager capable of mapping OH temperature (at ∼87 km altitude) were made from Bear Lake Observatory, Utah (41.9°N, 111.6°W) and Ft. Collins, Colorado (40.6°N, 105°W) within the same time period. The “mean day” lidar data for the spring and fall periods investigated here each indicate an average amplitude variation of ∼2–5 K over the depth of the OH layer but distinct phases of <1-hr LST and ∼7-hr LST, respectively, for the 8-hr component. The Temperature Mapper data are in excellent agreement with these findings but in addition have shown that the amplitude of this tidal component can vary by as much as an order of magnitude (1.5–15 K) on a night-by-night basis resulting in an apparent 8-hr dominance of the nocturnal variation during investigated portions of the spring and fall seasons with little or no diurnal and semi-diurnal variability evident. Reports of terdiurnal tidal measurements in the mid-latitude nightglow emissions are exceptionally rare and have yet to be modeled. These innovative joint measurements pave the way for new research in this important area.