The outstanding tropical land climate characteristic over the past decades is rapid warming, with no significant large-scale precipitation trends. This warming is expected to continue but the effects ...on tropical vegetation are unknown. El Niño-related heat peaks may provide a test bed for a future hotter world. Here we analyse tropical land carbon cycle responses to the 2015/16 El Niño heat and drought anomalies using an atmospheric transport inversion. Based on the global atmospheric CO₂ and fossil fuel emission records, we find no obvious signs of anomalously large carbon release compared with earlier El Niño events, suggesting resilience of tropical vegetation. We find roughly equal net carbon release anomalies from Amazonia and tropical Africa, approximately 0.5 PgC each, and smaller carbon release anomalies from tropical East Asia and southern Africa. Atmospheric CO anomalies reveal substantial fire carbon release from tropical East Asia peaking in October 2015 while fires contribute only a minor amount to the Amazonian carbon flux anomaly. Anomalously large Amazonian carbon flux release is consistent with downregulation of primary productivity during peak negative near-surface water anomaly (October 2015 to March 2016) as diagnosed by solar-induced fluorescence. Finally, we find an unexpected anomalous positive flux to the atmosphere from tropical Africa early in 2016, coincident with substantial CO release.
This article is part of a discussion meeting issue 'The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications'.
A novel radiative transfer model for a scattering layer in a plane-parallel thermally emitting atmosphere is described. The model is designed for computing radiances in iterative remote-sensing ...methods where computational efficiency is of utmost importance. The model combines a single-scatter method with the standard Eddington’s second approximation technique, which is required for higher-order scattering. The single-scattering model uses tabulated scattering properties. The accuracy of the hybrid model, relative to an exact doubling-adding model, is compared with three other approximate methods (nonscattering, single-scattering, and Eddington). Brightness temperature errors for simulated ice and water clouds are shown for various particle size distributions in both microwave (1–50
cm
-1) and infrared (300–3000
cm
-1) parts of the spectrum. As indicated by a root-mean-square measure of brightness temperature error over outgoing directions, the hybrid model is a significant improvement over the standard Eddington model in the regions of the infrared where scattering is important. Computer source code (written in FORTRAN) for implementing the hybrid scattering model is available from the authors.
A novel microwave technique for simultaneously retrieving cirrus ice water path (IWP) and characteristic ice particle size is described. The retrieval algorithm exploits radiance measurements made at ...150 and 220 GHz by the airborne Millimeter-Wave Imaging Radiometer (MIR).
A novel microwave technique for simultaneously retrieving cirrus ice water path (IWP) and characteristic ice particle size is described. The retrieval algorithm exploits radiance measurements made at ...150 and 220 GHz by the airborne Millimeter-Wave Imaging Radiometer (MIR). Other MIR channels additionally are used to test for the presence of liquid clouds and precipitation, which otherwise would have a contaminating effect on the retrievals. Forward radiative transfer modeling was used to generate a two-dimensional retrieval table in which brightness-temperature depressions (relative to clear-sky values) for both microwave channels were recorded as functions of IWP and characteristic particle size for gamma distributions of ice particles. Retrieval errors due to particle shape, size distribution, clear-sky water vapor variability, cirrus-cloud altitude variability, and instrument noise were estimated using Monte Carlo analysis. Particle shape uncertainty is believed to be the dominant source of retrieval error. The technique is demonstrated using MIR data recorded on the National Aeronautics and Space Administration ER-2 aircraft during the Tropical Ocean and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment experiment in the tropical western Pacific Ocean in 1993. The retrieval technique with MIR data is suited only to high-IWP clouds with large ice particles, such as thick frontal cirrus and convective anvils. The general methodology, however, is applicable to higher frequencies that have greatly increased sensitivity to thinner cirrus.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Ferrimagnetic iron garnet crystals form the basis of magnetooptic magnetic field sensors which offer high sensitivity, broad-band frequency response, and compatibility with fiber optics. Recent ...developments at NIST promise still greater performance for these devices in the near term. Specifically, new designs for magnetic field sensors, electric current sensors, and novel experimental iron garnet compositions demonstrate the potential for significantly improving the performance of these devices.< >
The scattering properties of cirrus clouds at submillimeter-wave frequencies are analyzed and characterized in this paper. This study lays a theoretical foundation for using radiometric measurements ...to investigate and monitor cirrus properties from high-flying aircraft or satellite. The significance of this capability is that it would provide data on the global distribution of cloud ice mass that is currently required to validate climate models. At present, these needs remain unmet by existing and planned observational systems.
In this study the brightness temperature depression (ΔTb
) of upwelling radiation due to cirrus clouds is simulated at 150, 220, 340, 500, 630, and 880 GHz. The effects of a range of size distributions, eight ice particle shapes, and different atmospheric profiles are modeled. The atmospheric transmission is high enough in the submillimeter windows to allow upper-tropospheric sensing from space, but absorption by water vapor reduces the sensitivity to lower cirrus clouds in a simply predictable manner. It is shown that frequencies above 500 GHz have adequate sensitivity to measure cirrus cloud properties. For these higher frequencies, the ΔTb
is closely proportional to ice water path (IWP) for median mass equivalent sphere diameters (D
me) above 125μm. The differing sensitivity with frequency allows two channels to determine particle size.
A two-channel Bayesian algorithm is developed to assess retrieval accuracy with a Monte Carlo error analysis procedure. Particle shape, size distribution width, and receiver noise are considered as error sources. The rms errors for a nadir view with 630/880 GHz are less than 40% for IWP > 5 g m−2andD
me> 100μm, while using an oblique viewing angle of 73° results in the same accuracy down to an IWP of 1 g m−2(visible optical depth less than 0.1). The two-channel algorithm and error analysis methods are used to show how submillimeter radiometer and millimeter radar measurements may be combined.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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