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Remotely sensed sea-surface temperature (SST) retrievals with a significant positive bias during the occurrence of upwelling phenomena along the southeastern coast of Brazil were reported in our companion paper. As a result, this paper proposes an automated bias correction algorithm to improve the MODIS long-wave multichannel SST (MCSST) retrievals during the abovementioned conditions in this region. In this paper, MODIS daytime SST data (SSTMODIS) and differences between brightness temperatures in MODIS channels 31 and 32 (BT31 − BT32) are analyzed simultaneously with hourly wind surface conditions, in situ SST at 0.3 and 10 m in depth (SSTbuoy03 and SSTbuoy10), and sensible and latent heat fluxes from the Cabo Frio buoy data (at 23° S, 42° W) during 2014. The obtained results show that some upwelling events present air temperature ($T_{\mathrm {air}}$) greater than SSTbuoy03 and low-atmospheric water vapor content. A simultaneous occurrence of these factors during upwelling conditions may lead to a warm-skin layer effect and may cause BT31 to be greater than SSTbuoy03 and BT31 − BT32 to be small (−0.18 °C ± 0.22 °C), affecting the MCSST performance. The proposed bias correction algorithm uses a least-squares curve between SSTbuoy03 and SSTMODIS retrievals when BT31 − BT32 ≤ 0.5 °C (i.e., dry atmospheric conditions). The bias correction algorithm has significantly improved the SSTMODIS bias (RMSE) from 1.43 °C to −0.2 °C (1.60 °C to 0.58 °C) when applied to 22 cloud-free pixels of MODIS during January–March of 2015. [ABSTRACT FROM AUTHOR]

In this paper, a simple algorithm is proposed to perform the nowcasting of rainfall in the tropical region. The algorithm applies global positioning system-derived precipitable water vapor (PWV) values and its second derivative for the short-term prediction of rainfall. The proposed algorithm incorporates the seasonal dependency of PWV values for the prediction of a rain event in the coming 5 min based on the past 30 min of PWV data. This proposed algorithm is based on the statistical study of four-year PWV and rainfall data from a station in Singapore and is validated using two-year independent data for the same station. The results show that the algorithm can achieve an average true detection rate and a false alarm rate of 87.7% and 38.6%, respectively. To analyze the applicability of the proposed algorithm, further validations are done using one-year data from one independent station from Singapore and two-year data from one station from Brazil. It is shown that the proposed algorithm performs well for both the independent stations. For the station from Brazil, the average true detection and false alarm rates are around 84.7% and 37%, respectively. All these observations suggest that the proposed algorithm is reliable and works well with a good detection rate. [ABSTRACT FROM AUTHOR]

A new tomographic method was developed with the main goal of mapping the ionosphere in the region of Brazil. The ionospheric background was estimated based on ionosonde and radio-occultation measurements to overcome the lack of data provided by climatological models in low-latitude regions. A new method of performing iterations of the conventional multiplicative algebraic reconstruction technique (MART) was also used in order to avoid nonilluminated cells and improve the spatial resolution. The quality assessment using independent ionosonde data during two weeks in 2013 showed a better performance of the proposed method in comparison to the international reference ionosphere, providing improvements of 31% for the F-layer peak height ${h}_{m}$ and 24% for the ionospheric peak of electron density ${N}_{m}$. The tomographic technique was also evaluated in the estimation of the total electron content (TEC) and in the single-frequency precise point positioning (PPP). Improvements of 59% in TEC and 31% in the single-frequency PPP were obtained in comparison to the results derived from global ionospheric maps. In addition, a better daily description of the ionosphere was obtained using the proposed method, where it was possible to detect the peak height increasing associated with the prereversal enhancement of the vertical plasma drift that occurs near sunset hours. The results reveal that the modified form of the MART tomographic technique can be considered a useful tool for technical and scientific communities involved in space weather, spatial geodesy, and telecommunications. [ABSTRACT FROM AUTHOR]