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E. R. Kursinski, S. Syndergaard, D. Flittner, D. Feng, G. Hajj, B. Herman, D. Ward, and T. Yunck

Abstract

A new remote sensing concept extrapolated from the GPS occultation concept is presented in which the signal frequencies are chosen to determine atmospheric water, temperature, and the geopotential of atmospheric pressure surfaces. Using frequencies near the 22- and 183-GHz water lines allows not only the speed of light to be derived as a GPS occultation but also derivation of profiles of absorption caused by atmospheric water. Given the additional water information, moisture and temperature as well as the geopotential of pressure surfaces can be separated and solved for. Error covariance results indicate that the accuracies of individual water profiles will be 0.5%–3% extending from roughly 1–75-km altitude. Temperature accuracies of individual profiles will be sub-Kelvin from ∼1- to 70-km altitude depending on latitude and season. Accuracies of geopotential heights of pressure will be 10–20 m from the surface to 60-km altitude. These errors are random such that climatological averages derived from this data will be significantly more accurate. Owing to the limb-viewing geometry, the along-track resolution is comparable to the 200–300 km of the GPS occultation observations, but the shorter 22- and 183-GHz wavelengths improve the diffraction-limited vertical resolution to 100–300 m. The technique can be also used to determine profiles of other atmospheric constituents such as upper-tropospheric and stratospheric ozone by using frequencies near strong lines of that constituent. The combined dynamic range, accuracy, vertical resolution, and ability to penetrate clouds far surpass that of any present or planned satellite sensors. A constellation of such sensors would provide an all-weather, global remote sensing capability including full sampling of the diurnal cycle for process studies related to water, climate research, and weather prediction in general.

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Erik Nilsson, Hans Bergström, Anna Rutgersson, Eva Podgrajsek, Marcus B. Wallin, Gunnar Bergström, Ebba Dellwik, Sebastian Landwehr, and Brian Ward

Abstract

Global oceans are an important sink of atmospheric carbon dioxide (CO2). Therefore, understanding the air–sea flux of CO2 is a vital part in describing the global carbon balance. Eddy covariance (EC) measurements are often used to study CO2 fluxes from both land and ocean. Values of CO2 are usually measured with infrared absorption sensors, which at the same time measure water vapor. Studies have shown that the presence of water vapor fluctuations in the sampling air potentially results in erroneous CO2 flux measurements resulting from the cross sensitivity of the sensor. Here measured CO2 fluxes from both enclosed-path Li-Cor 7200 sensors and open-path Li-Cor 7500 instruments from an inland measurement site are compared with a marine site. Also, new quality control criteria based on a relative signal strength indicator (RSSI) are introduced. The sampling gas in one of the Li-Cor 7200 instruments was dried by means of a multitube diffusion dryer so that the water vapor fluxes were close to zero. With this setup the effect that cross sensitivity of the CO2 signal to water vapor can have on the CO2 fluxes was investigated. The dryer had no significant effect on the CO2 fluxes. The study tested the hypothesis that the cross-sensitivity effect is caused by hygroscopic particles such as sea salt by spraying a saline solution on the windows of the Li-Cor 7200 instruments during the inland field test. The results confirm earlier findings that sea salt contamination can affect CO2 fluxes significantly and that drying the sampling air for the gas analyzer is an effective method for reducing this signal contamination.

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G. Reverdin, S. Morisset, H. Bellenger, J. Boutin, N. Martin, P. Blouch, J. Rolland, F. Gaillard, P. Bouruet-Aubertot, and B. Ward

Abstract

This study describes how the hull temperature (Ttop) measurements from multisensor surface velocity program (SVP) drifters can be combined with other measurements to provide quantitative information on near-surface vertical temperature stratification during large daily cycles. First, Ttop is compared to the temperature measured at 17 -cm depth from a float tethered to the SVP drifter. These 2007–12 SVP drifters present a larger daily cycle by 1%–3% for 1°–2°C daily cycle amplitudes, with a maximum difference close to the local noon. The difference could result from flow around the SVP drifter in the presence of temperature stratification in the top 20 cm of the water column but also from a small influence of internal drifter temperature on Ttop. The largest differences were found for small drifters (Technocean) for very large daily cycles, as expected from their shallower measurements. The vertical stratification is estimated by comparing these hull data with the deeper T or conductivity C measurements from Sea-Bird sensors 25 (Pacific Gyre) to 45 cm (MetOcean) below the top temperature sensor. The largest stratification is usually found near local noon and early afternoon. For a daily cycle amplitude of 1°C, these differences with the upper level are in the range of 3%–5% of the daily cycle for the Pacific Gyre drifters and 6%–10% for MetOcean drifters with the largest values occurring when the midday sun elevation is lowest. The relative differences increase for larger daily cycles, and the vertical profiles become less linear. These estimated stratifications are well above the uncertainty on Ttop.

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