Satellite-based monitoring and prediction of tropical cyclone intensity and movement

ABSTRACT. Capabilities of meteorological satellites have gone a long way in meeting requirements of synoptic analysis and forecasting of tropical cyclones. This paper shows the impact made by the satellite data in the intensity estimation and track prediction of tropical cyclones in the Indian Seas and also reviews the universally applied Dvorak algorithm for performing tropical cyclone intensity analysis. Extensive use of Dvorak's intensity estimation scheme has revealed many of its limitations and elements of subjectivity in the analysis of tropical cyclones over the Arabian Sea and the Bay of Bengal, which, like cyclones in other ocean basins, also exhibit wide structural variability as seen in the satellite imagery. Satellite-based cyclone tracking techniques include: (i) use of satellite-derived mean wind flow, (ii) animation of sequence of satellite images and extrapolation of the apparent motion of the cloud system and (iii) monitoring changes in the upper level moisture patterns in the water vapour absorption channel imagery. Satellite-based techniques on tropical cyclone intensity estimation and track prediction have led to very significant improvement in disaster warning and consequent saving of life and property.

Ultrathin and Simple Frequency Selective Rasorber Based on Ferrite Absorber with Embedded Epsilon-Near-Zero Tunneling Channels

An ultrathin and simple frequency-selective rasorber (FSR) with a passband located within a wide absorption band is proposed. The ultrawide absorption band is obtained by employing commercial magnetic materials in the absorption channel and the passband is realized using epsilon-near-zero (ENZ) tunneling waveguides. The attractively ultrathin and simple feature is achieved by utilizing tunneling effect at the cutoff frequency of metallic waveguides with arbitrary length, permitting the overall thickness shrink into to the same as that of the absorber.

Ultrathin and Simple Frequency Selective Rasorber Based on Ferrite Absorber with Embedded Epsilon-Near-Zero Tunneling Channels

An ultrathin and simple frequency-selective rasorber (FSR) with a passband located within a wide absorption band is proposed. The ultrawide absorption band is obtained by employing commercial magnetic materials in the absorption channel and the passband is realized using epsilon-near-zero (ENZ) tunneling waveguides. The attractively ultrathin and simple feature is achieved by utilizing tunneling effect at the cutoff frequency of metallic waveguides with arbitrary length, permitting the overall thickness shrink into to the same as that of the absorber.

Monitoring precipitation convective clouds with collocated hyperspectral infrared sounder and imager measurements

<p>Typically, DCCs are identified by 11 µm band brightness temperature (BT11) lower than a fixed BT threshold. Another method of combining the brightness temperature difference (BTD) between a water vapor absorption channel and a window channel to its measurement noise ratio (BNR) is adopted and applied to DCC identification. This BNR method improves the DCC detections over the legacy method because it is less contaminated with high clouds not thick and bright enough. BNR detects fewer DCCs than BT11, but with more confidence. </p><p>Using observations of the collocated Cross-track Infrared Sounder (CrIS) and the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (SNPP) from 2017 to 2018, the results show BNR has better performances than BT11 for identifying the DCC and monitoring reflective solar bands. When comparing to BT11, BNR has more robust and invariant time series of monthly reflectance for all RSBs. Because BNR affects more on the left tails (less reflective) of the histograms than the mode reflectance, the improvement is more significant on the mean values than the modes. This method can be applied to other imagers with collocated advanced infrared sounders for detecting DCCs and monitoring the calibration stabilities of RSBs. </p><p>Recently, the hyperspectral infrared atmospheric sounders onboard China’s next-generation FengYun satellites, i.e. the Geosynchronous Interferometric InfraRed Sounder (GIIRS) on the FengYun-4 geostationary satellite series and the Hyperspectral Infrared Atmospheric Sounder (HIRAS) on the FengYun-3 polar orbiting meteorological satellite series, are in operation. Flown onboard the same platforms, the collocated (consistent in time and space) infrared sounders and imagers, provide mount of match-up measurements for the study of methodology and process for synergistic use of both infrared sounder and imager for multiple applications. The findings will provide scientific evidences for further enhancements and applications of future FengYun satellites and its observing system.</p>

Quantification of uncertainties of water vapour column retrievals using future instruments

This study presents a quantification of uncertainties of total column water vapour retrievals based on simulated near-infrared measurements of upcoming instruments. The concepts of three scheduled spectrometers were taken into account: OLCI (Ocean and Land Color Instrument) on Sentinel-3, METimage on an EPS-SG (EUMETSAT Polar System – Second Generation) satellite and FCI (Flexible Combined Imager) on MTG (Meteosat Third Generation). Optimal estimation theory was used to estimate the error of a hypothetical total water vapour column retrieval for 27 different atmospheric cases. The errors range from 100% in very dry cases to 2% in humid cases with a very high surface albedo. Generally, the absolute uncertainties increase with higher water vapour column content due to H2O-saturation and decrease with a brighter surface albedo. Uncertainties increase with higher aerosol optical thickness, apart from very dark cases. Overall, the METimage channel setting enables the most accurate retrievals. The retrieval using the MTG-FCI build-up has the highest uncertainties apart from very bright cases. On the one hand, a retrieval using two absorption channels increases the accuracy, in some cases by one order of magnitude, in comparison to a retrieval using just one absorption channel. On the other hand, a retrieval using three absorption channels has no significant advantage over a two-absorption channel retrieval. Furthermore, the optimal position of the absorption channels was determined using the concept of the "information content". For a single channel retrieval, a channel at 900 or 915 nm has the highest mean information content over all cases. The second absorption channel is ideally weakly correlated with the first one, and therefore positioned at 935 nm, in a region with stronger water vapour absorption.

Quantification of uncertainties of water vapour column retrievals using future instruments

This study presents a quantification of uncertainties of water vapour retrievals based on near infrared measurements of upcoming instruments. The concepts of three scheduled spectrometer were taken into account: OLCI (Ocean and Land Color Instrument) on Sentinel-3, METimage on MetOp (Meteorological Operational Satellite) and FCI (Flexible Combined Imager) on MTG (Meteosat Third Generation). Optimal estimation theory was used to estimate the error of an hypothetical total water vapour column retrieval for 27 different atmospheric cases. The errors range from 100% in very dry cases to 2% in humid cases with a very high surface albedo. Generally the absolute uncertainties increase with higher water vapour column content due to H2O-saturation and decrease with a brighter surface albedo. Uncertainties increase with higher aerosol optical thickness, apart from very dark cases. Overall the METimage channel setting enables the most accurate retrievals. The retrieval using the MTG-FCI buildup has the highest uncertainties apart from very bright cases. A retrieval using two absorption channels increases the accuracy, in some cases by one order of magnitude, in comparison to a retrieval using just one absorption channel. On the other hand, a retrieval using three absorption channels has no significant advantage over a two-absorption channel retrieval. Furthermore, the optimal position of the absorption channels was determined using the concept of the "information content". For a single channel retrieval a channel at 900 or 915 nm has the highest mean information contents over all cases. The second absorption channel is ideally weakly correlated with the first one, thus positioned at 935 nm, in a region with stronger water vapour absorption.

A MODIS Dual Spectral Rain Algorithm

The Moderate Resolution Imaging Spectroradiometer (MODIS) dual spectral rain algorithm (MODRA) is developed for rain retrievals over the northern midlatitudes. The reflectance of the MODIS water vapor absorption channel at 1.38 μm (R1.38 μm) has a potential to represent the cloud-top height displayed by the brightness temperature (TB) of the MODIS channel at 11 μm, because of an excellent negative relationship (correlation coefficient ≤−0.9) between R1.38 μm and TB11 μm for optically thick clouds with reflectance (R0.65 μm) greater than 0.75. With a training rainfall dataset from the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) aboard the same Aqua satellite platform, two MODIS channels (R1.38 μm and R0.65 μm) are applied to form multiregression curves to estimate daytime rainfall. Results demonstrate that the instantaneous rain rates from MODRA, independent AMSR-E rainfall products, and surface rain gauge measurements are consistent. This study explores a new way to estimate rainfall from MODIS water vapor and cloud channels. The resulting technique could be applied to other similar satellite instruments for rain retrievals.

Calibration of Sun Radiometer–Based Atmospheric Water Vapor Retrievals Using GPS Meteorology

A study of the validation and calibration process for integrated water vapor (IWV) measurements derived from sun radiometry at the 940-nm solar absorption channel employed in the Aerosol Robotic Network (AERONET) Aerosol Canada (AEROCAN) is presented. The sun radiometer data are compared with GPS meteorology records used as a reference. Three Canadian sites from different climatic regimes covering the period 2000–04 are considered. The observations from five different sun radiometers (IWV-SUN) were processed using the initial AERONET IWV retrieval procedure (V1) whereas GPS-derived IWV (IWV-GPS) was retrieved using “GPSpace” software developed by the Geodetic Survey division of Natural Resources Canada. A sensitivity study is carried out to highlight the influence of both central wavelength and signal amplitude on the 940-nm filter characteristics, which are instrument dependent and can drift due to aging. The comparison between IWV-SUN (V1) and IWV-GPS shows an average rmse of 0.23 ± 0.11 g cm−2 (22%) and a mean bias of −0.09 ± 0.16 g cm−2 (9%). Furthermore, it is shown that the use of GPS for determining the 940-nm channel calibration constants for the solar radiometers improves IWV retrievals (rmse reduced by about 35% and bias by a factor of 3–10) without any knowledge of the 940-nm filter characteristics. These results are discussed within the context of the new AERONET IWV processing procedure (V2), which accounts for solar 940-nm region filter characteristics. The GPS receiver technique appears to be a powerful calibration tool because of its continuous observation capability, its robustness, and its operational simplicity.

Laser Induced Synthesis: Condensation of Acrylonitrile on Carvone

Laser irradiation of R(–) carvone in solution in acrylonitrile within the absorption band of its n−π* transition (≃350 nm) leads to the formation of cyclobutanic adducts, together with traces of camphocarvone.The carvone transformation is complete and appears with high quantum efficiency. The quantum yield for intermolecular reaction is intensity dependent (13–30%). This is ascribed to the fact that the reaction takes place via both a one and a two-photon absorption channel, the second being even more efficient.