Tropical land carbon cycle responses to 2015/16 El Niño as recorded by atmospheric greenhouse gas and remote sensing data

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’.

Monitoring emissions from the 2015 Indonesian fires using CO satellite data

Southeast Asia, in particular Indonesia, has periodically struggled with intense fire events. These events convert substantial amounts of carbon stored as peat to atmospheric carbon dioxide (CO₂) and significantly affect atmospheric composition on a regional to global scale. During the recent 2015 El Niño event, peat fires led to strong enhancements of carbon monoxide (CO), an air pollutant and well-known tracer for biomass burning. These enhancements were clearly observed from space by the Infrared Atmospheric Sounding Interferometer (IASI) and the Measurements of Pollution in the Troposphere (MOPITT) instruments. We use these satellite observations to estimate CO fire emissions within an inverse modelling framework. We find that the derived CO emissions for each sub-region of Indonesia and Papua are substantially different from emission inventories, highlighting uncertainties in bottom-up estimates. CO fire emissions based on either MOPITT or IASI have a similar spatial pattern and evolution in time, and a 10% uncertainty based on a set of sensitivity tests we performed. Thus, CO satellite data have a high potential to complement existing operational fire emission estimates based on satellite observations of fire counts, fire radiative power and burned area, in better constraining fire occurrence and the associated conversion of peat carbon to atmospheric CO₂ A total carbon release to the atmosphere of 0.35-0.60 Pg C can be estimated based on our results.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'.

Carbon monoxide total column retrievals by use of the measurements of pollution in the troposphere airborne test radiometer

The Measurements of Pollution in the Troposphere (MOPITT) Airborne Test Radiometer (MATR) uses gas correlation filter radiometry from high-altitude aircraft to measure tropospheric carbon monoxide. This radiometer is used in support of the ongoing validation campaign for the MOPITT instrument aboard the Earth Observation System Terra satellite. A recent study of MATR CO retrievals that used data from the autumn of 2001 in the western United States is presented. Retrievals of the CO total column were performed and compared to in situ sampling with less than 10% retrieval error. Effects that influence retrieval, such as instrument sensitivity, retrieval sensitivity, and the bias between observations and the radiative transfer model, are discussed. Comparisons of MATR and MOPITT retrievals show promising consistency. A preliminary interpretation of MATR results is also presented.

Fiber-optic Faraday-effect magnetic-field sensor based on flux concentrators

The principles and performance of a fiber-optic Faraday-effect magnetic-field sensor designed around an yttrium-iron-garnet (YIG) sensing element and two flux concentrators are described. The system design exploits the technique of polarization-rotated reflection in which a single polarization-maintaining optical fiber links the sensor head to the optical source and detection system. In the sensing head, ferrite flux concentrators are magnetically coupled to the YIG sensing element to achieve maximum sensitivity. The system exhibits a noise equivalent field of 6 pT/√Hz and a 3-dB bandwidth of~10 MHz.

Domain effects in Faraday effect sensors based on iron garnets

Domain-induced diffraction effects produced by two iron garnet thick films and two bulk crystals are compared. The thick films, characterized by a serpentine magnetic domain structure, produced nonlinear response functions; this is in qualitative agreement with a one-dimensional diffraction model. Bulk iron garnet crystals, which exhibited a complex three-dimensional domain structure, produced qualitatively similar effects that diminished with increasing crystal length. Differential signal processing resulted in a linear signal for the thick films and a primarily sinusoidal response for the bulk crystals.

Temperature dependence of the Verdet constant in several diamagnetic glasses

Measured temperature dependences of the Verdet constants of SiO(2), SF-57, and BK-7 are approximately 10(-4)/K within 3-20% of Becquerel formula estimates.

Determination of optical constants by angle scanning reflectometry

Reflectance measurements made on an Fe film over a wide range of angles of incidence are curve-fitted to extract the optical constants n and k. Problems with surface oxide layers are eliminated by making the reflectance measurements through the substrate. The experimental uncertainties of n and k are determined by a rigorous x(2) analysis. The experimentally determined optical constants are found to be considerably larger than values found in the literature.

Jones matrix analysis of incident angle effects in magnetooptic storage media

A ray-tracing technique employing Jones matrices was used to model the polarization state of the reflected wavefront as a function of numerical aperture for the various types of magnetooptic media. The average reflectance and MO signal for differential readout were calculated for different numerical apertures by integrating over the wavefront. Quadrilayer structures which are designed to maximize the readout SNR are most affected by incident angle effects.

Effects of incident angle on readout in magnetooptic storage media

The effects of incident angle on the readout SNR of a magnetooptic storage system employing the differential detection system were theoretically investigated. The most important parameters which depend on incident angle were found to be the Kerr reflectance and the phase difference between the two components of the reflected wave. In particular, the phase difference was found to depend strongly on incident angle for structures which are strongly antireflective.

Optical probing of magnetic inert layers

The thickness of a magnetic inert layer on top of a ferrite head sample was measured by probing the longitudinal Kerr effect as a function of the angle of incidence of a laser beam. Our computerized measuring system used a simple single-detector setup to derive polarization information from a Kerr-reflected beam as the incident angle was scanned. The results were analyzed using a general theory of reflection from magnetic stratified media. The experimental results indicate that the possible inert-layer thickness values are given by (50 +/- 10) + 60 x N nm, where the order N equals 0, 1, 2, 3, or 4.