Robert P. Lowe

Bio: Robert P. Lowe is an academic researcher from University of Western Ontario. The author has contributed to research in topics: Airglow & Mesopause. The author has an hindex of 24, co-authored 44 publications receiving 7484 citations.

Localization of the complex spectrum: the S transform

Abstract: The S transform, which is introduced in the present correspondence, is an extension of the ideas of the continuous wavelet transform (CWT) and is based on a moving and scalable localizing Gaussian window. It is shown to have some desirable characteristics that are absent in the continuous wavelet transform. The S transform is unique in that it provides frequency-dependent resolution while maintaining a direct relationship with the Fourier spectrum. These advantages of the S transform are due to the fact that the modulating sinusoids are fixed with respect to the time axis, whereas the localizing scalable Gaussian window dilates and translates.

Localisation of the complex spectrum : The S transform

Abstract: The S transform, an extension to the ideas of the Gabor transform and the Wavelet transform, is based on a moving and scalable localising Gaussian window and is shown here to have characteristics that are superior to either of the transforms. The S transform is fully convertible both forward and inverse from the time domain to the 2-D frequency translation (time) domain and to the familiar Fourier frequency domain. Parallel to the translation (time) axis, the S transform collapses as the Fourier transform. The amplitude frequency-time spectrum and the phase frequency-time spectrum are both useful in defining local spectral characteristics. The superior properties of the S transform are due to the fact that the modulating sinusoids are fixed with respect to the time axis while the localising scalable Gaussian window dilates and translates. As a result, the phase spectrum is absolute in the sense that it is always referred to the origin of the time axis, the fixed reference point. The real and imaginary spectrum can be localised independently with a resolution in time corresponding to the period of the basis functions in question. Changes in the absolute phase ofa constituent frequency can be followed along the time axis and useful information can be extracted. An analysis of a sum of two oppositely progressing chirp signals provides a spectacular example of the power of the S transform. Other examples of the applications of the Stransform to synthetic as well as real data are provided.

Atmospheric Chemistry Experiment (ACE): Mission overview.

Abstract: SCISAT-1, also known as the Atmospheric Chemistry Experiment (ACE), is a Canadian satellite mission for remote sensing of the Earth's atmosphere. It was launched into low Earth circular orbit (altitude 650 km, inclination 74°) on 12 Aug. 2003. The primary ACE instrument is a high spectral resolution (0.02 cm-1) Fourier Transform Spectrometer (FTS) operating from 2.2 to 13.3 μm (750-4400 cm-1). The satellite also features a dual spectrophotometer known as MAESTRO with wavelength coverage of 285-1030 nm and spectral resolution of 1-2 nm. A pair of filtered CMOS detector arrays records images of the Sun at 0.525 and 1.02 μm. Working primarily in solar occultation, the satellite provides altitude profile information (typically 10-100 km) for temperature, pressure, and the volume mixing ratios for several dozen molecules of atmospheric interest, as well as atmospheric extinction profiles over the latitudes 85°N to 85°S. This paper presents a mission overview and some of the first scientific results. Copyright 2005 by the American Geophysical Union.

WINDII, the wind imaging interferometer on the Upper Atmosphere Research Satellite

Abstract: The WIND imaging interferometer (WINDII) was launched on the Upper Atmosphere Research Satellite (UARS) on September 12, 1991. This joint project, sponsored by the Canadian Space Agency and the French Centre National d'Etudes Spatiales, in collaboration with NASA, has the responsibility of measuring the global wind pattern at the top of the altitude range covered by UARS. WINDII measures wind, temperature, and emission rate over the altitude range 80 to 300 km by using the visible region airglow emission from these altitudes as a target and employing optical Doppler interferometry to measure the small wavelength shifts of the narrow atomic and molecular airglow emission lines induced by the bulk velocity of the atmosphere carrying the emitting species. The instrument used is an all-glass field-widened achromatically and thermally compensated phase-stepping Michelson interferometer, along with a bare CCD detector that images the airglow limb through the interferometer. A sequence of phase-stepped images is processed to derive the wind velocity for two orthogonal view directions, yielding the vector horizontal wind. The process of data analysis, including the inversion of apparent quantities to vertical profiles, is described.

Review of mesospheric temperature trends

Abstract: In recent times it has become increasingly clear that releases of trace gases from human activity have a potential for causing change in the upper atmosphere. However, our knowledge of systematic changes and trends in the temperature of the mesosphere and lower thermosphere is relatively limited compared to the Earths lower atmosphere, and not much effort has been made to synthesize these results so far. In this article, a comprehensive review of long-term trends in the temperature of the region from 50 to 100 km is made on the basis of the available up-to-date understanding of measurements and model calculations. An objective evaluation of the available data sets is attempted, and important uncertainly factors are discussed. Some natural variability factors, which are likely to play a role in modulating temperature trends, are also briefly touched upon. There are a growing number of experimental results centered on, or consistent with, zero temperature trend in the mesopause region (80–100 km). The most reliable data sets show no significant trend but an uncertainty of at least 2 K/decade. On the other hand, a majority of studies indicate negative trends in the lower and middle mesosphere with an amplitude of a few degrees (2–3 K) per decade. In tropical latitudes the cooling trend increases in the upper mesosphere. The most recent general circulation models indicate increased cooling closer to both poles in the middle mesosphere and a decrease in cooling toward the summer pole in the upper mesosphere. Quantitatively, the simulated cooling trend in the middle mesosphere produced only by CO 2 increase is usually below the observed level. However, including other greenhouse gases and taking into account a “thermal shrinking” of the upper atmosphere result in a cooling of a few degrees per decade. This is close to the lower limit of the observed nonzero trends. In the mesopause region, recent model simulations produce trends, usually below 1 K/decade, that appear to be consistent with most observations in this region

The HITRAN 2008 molecular spectroscopic database

Abstract: This paper describes the contents of the 2016 edition of the HITRAN molecular spectroscopic compilation. The new edition replaces the previous HITRAN edition of 2012 and its updates during the intervening years. The HITRAN molecular absorption compilation is composed of five major components: the traditional line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, infrared absorption cross-sections for molecules not yet amenable to representation in a line-by-line form, collision-induced absorption data, aerosol indices of refraction, and general tables such as partition sums that apply globally to the data. The new HITRAN is greatly extended in terms of accuracy, spectral coverage, additional absorption phenomena, added line-shape formalisms, and validity. Moreover, molecules, isotopologues, and perturbing gases have been added that address the issues of atmospheres beyond the Earth. Of considerable note, experimental IR cross-sections for almost 300 additional molecules important in different areas of atmospheric science have been added to the database. The compilation can be accessed through www.hitran.org. Most of the HITRAN data have now been cast into an underlying relational database structure that offers many advantages over the long-standing sequential text-based structure. The new structure empowers the user in many ways. It enables the incorporation of an extended set of fundamental parameters per transition, sophisticated line-shape formalisms, easy user-defined output formats, and very convenient searching, filtering, and plotting of data. A powerful application programming interface making use of structured query language (SQL) features for higher-level applications of HITRAN is also provided.

Tropical tropopause layer

Abstract: [1] Observations of temperature, winds, and atmospheric trace gases suggest that the transition from troposphere to stratosphere occurs in a layer, rather than at a sharp “tropopause.” In the tropics, this layer is often called the “tropical tropopause layer” (TTL). We present an overview of observations in the TTL and discuss the radiative, dynamical, and chemical processes that lead to its time-varying, three-dimensional structure. We present a synthesis definition with a bottom at 150 hPa, 355 K, 14 km (pressure, potential temperature, and altitude) and a top at 70 hPa, 425 K, 18.5 km. Laterally, the TTL is bounded by the position of the subtropical jets. We highlight recent progress in understanding of the TTL but emphasize that a number of processes, notably deep, possibly overshooting convection, remain not well understood. The TTL acts in many ways as a “gate” to the stratosphere, and understanding all relevant processes is of great importance for reliable predictions of future stratospheric ozone and climate.

The Total Carbon Column Observing Network

Abstract: A global network of ground-based Fourier transform spectrometers has been founded to remotely measure column abundances of CO_2, CO, CH_4, N_(2)O and other molecules that absorb in the near-infrared. These measurements are directly comparable with the near-infrared total column measurements from space-based instruments. With stringent requirements on the instrumentation, acquisition procedures, data processing and calibration, the Total Carbon Column Observing Network (TCCON) achieves an accuracy and precision in total column measurements that is unprecedented for remotesensing observations (better than 0.25% for CO_2). This has enabled carbon-cycle science investigations using the TCCON dataset, and allows the TCCON to provide a link between satellite measurements and the extensive ground-based in situ network.

Simulation of secular trends in the middle atmosphere, 1950–2003

Abstract: [1] We have used the Whole Atmosphere Community Climate Model to produce a small (three-member) ensemble of simulations of the period 1950–2003. Comparison of model results against available observations shows that for the most part, the model is able to reproduce well the observed trends in zonal mean temperature and ozone, both as regards their magnitude and their distribution in latitude and altitude. Calculated trends in water vapor, on the other hand, are not at all consistent with observations from either the HALOE satellite instrument or the Boulder, Colorado, hygrosonde data set. We show that such lack of agreement is actually to be expected because water vapor has various sources of low-frequency variability (heating due to volcanic eruptions, the quasi-biennial oscillation and El Nino–Southern Oscillation) that can confound the determination of secular trends. The simulations also reveal the presence of other interesting behavior, such as the lack of any significant temperature trend near the mesopause, a decrease in the stratospheric age of air, and the rare occurrence of an extremely disturbed Southern Hemisphere winter.