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Multiwavelength solar irradiance measurements between 400 and 900 nm were made on cloudless days in Tucson, Arizona, over a 30-month period between March 2010 and August 2012. They were analyzed to simultaneously retrieve aerosol optical depth (AOD) and ozone column abundance and to examine their monthly variation. These retrievals were compared with results from a similar study done at the same location between 1975 and 1977. The near tripling of population in Tucson over the past 35 years may have contributed to a 19% increase in the AOD, and the annual-mean ozone column abundance was found to be 11% lower than that inferred during the mid-1970s. [ABSTRACT FROM AUTHOR]

Previous analyses of the Earth's annual cycle and its trends have utilized surface temperature data sets. Here we introduce a new analysis of the global and hemispheric annual cycle using a satellite remote sensing derived data set during the period 1979-2009, as determined from the lower tropospheric (LT) channel of the MSU satellite. While the surface annual cycle is tied directly to the heating and cooling of the land areas, the tropospheric annual cycle involves additionally the gain or loss of heat between the surface and atmosphere. The peak in the global tropospheric temperature in the 30 year period occurs on 10 July and the minimum on 9 February in response to the larger land mass in the Northern Hemisphere. The actual dates of the hemispheric maxima and minima are a complex function of many variables which can change from year to year thereby altering these dates. Here we examine the time of occurrence of the global and hemispheric maxima and minima lower tropospheric temperatures, the values of the annual maxima and minima, and the slopes and significance of the changes in these metrics. The statistically significant trends are all relatively small. The values of the global annual maximum and minimum showed a small, but significant trend. Northern and Southern Hemisphere maxima and minima show a slight trend toward occurring later in the year. Most recent analyses of trends in the global annual cycle using observed surface data have indicated a trend toward earlier maxima and minima. [ABSTRACT FROM AUTHOR]

The global positioning system (GPS) radio occultation (RO) technique has demonstrated the ability to precisely probe earth’s atmosphere globally with high vertical resolution. However, the lowermost troposphere still presents some challenges for the technique. Over moist marine areas, especially in subtropical regions, a very large negative moisture gradient often exists across the thermal inversion capping the marine boundary layer (MBL), which frequently causes superrefraction (SR), or ducting. In the presence of SR, the reconstruction of refractivity from RO data becomes an ill-posed inverse problem. This study shows that one given RO bending angle profile is consistent with a continuum (an infinite number) of refractivity profiles. The standard Abel retrieval gives the minimum refractivity solution of the continuum and thus produces the largest negative bias, consistent with a negative bias often present in the retrieved refractivity profiles in the moist lower troposphere. By applying a simple linear parameterization of the refractivity structure within and just below the SR layer, an analytical relation between the Abel-retrieved refractivity and a continuum of solutions is derived. Combining the Abel retrieval and the analytical relation with some physical constraints, a novel approach is developed to reconstruct the vertical refractivity structure within and below the SR layer. Numerical simulation studies in this paper have demonstrated the great potential of the reconstruction method to provide a much-improved retrieval in the presence of SR, and the method should greatly enhance the ability to measure the MBL structure globally using the GPS RO technique. [ABSTRACT FROM AUTHOR]

This paper describes the details of a fast, linear, forward-inverse refractive index mapping operator that can be used for assimilation of occultation data of various kinds into NWP models. Basically, the mapping consists of the integration of the refractive index along finite straight lines, mimicking the observational geometry as well as the subsequent retrieval of a refractive index profile, assuming spherical symmetry. Line integrals are discretized such that the refractivity is evaluated along the horizontal at fixed levels that can be chosen to coincide with the pressure levels of an NWP model. Integration of the hydrostatic equation at a large number of locations is thereby avoided. The mapping operator is tested using an idealized model of a weather front with large horizontal gradients. Mapped refractivity profiles are compared with retrieved refractivity profiles obtained via accurate 3D ray tracing simulations of GPS radio occultation events with ray path tangent points near the weather front. The simulations indicate that the mapping is a good representation of occultation measurements, including the influence large horizontal gradients have on retrieved refractivity profiles. To further the results, a simple ad hoc modification is introduced to approximately account for the ray path bending near the tangent points. The forward-inverse mapping allows for the near cancellation of otherwise crude approximations—for example, straight-line propagation—and the general concept could perhaps be adapted for the development of fast and accurate observation operators for the assimilation of other types of remote sensing data. [ABSTRACT FROM AUTHOR]

The Global Positioning System/Meteorology (GPS/MET) project is an active satellite-to-satellite remote sensing experiment using the radio occultation technique. Due to the atmospheric index of refraction and gradient of the index of refraction, GPS signals propagate through the earth's atmosphere along a slightly curved path and with slightly retarded speeds. When these signals arrive at a receiver aboard a low earth orbit satellite, the receiver records an excess phase delay compared with the phase delay of a straight line propagation in a vacuum. Using the Abel integral equations, the phase delay rates with time can be converted into the atmospheric index of refraction profile; then, using the hydrostatic equation, the pressure and tem-perature profiles may be derived. This paper describes the principles of the GPS/MET occultation experiment and the detailed data analysis procedure. Data smoothing technique and error analysis are also discussed. Some GPS/MET intermediate and final retrieval results, such as ray bending angle and temperature and pressure profiles, are presented for illustration. Although random noise in the GPS/MET measurements leads to an uncertainty of ;0.1--0.3 K in the retrieved temperatures, comparisons of the GPS/MET retrieval results with radiosonde measurements, other remote sensing observations, and numerical analyses show that without the multipath corrections the GPS/MET temperature profiles accurate to within 1°--2°C can be obtained from ;5--7 to ;40 km above the ground. Despite the fact that a few outstanding problems in the GPS/MET data retrievals remain to be addressed, overall the GPS/MET occultation method has been demonstrated to be capable of producing accurate, all-weather, round-the-clock, global refractive index, density, pressure, and temperature profiles of the troposphere and stratosphere. [ABSTRACT FROM AUTHOR]