Abstract
There is pressing demand for knowledge improvement of the integrated water vapor (IWV) distribution in regions affected by heat islands that are associated with extreme rainfall events such as in the metropolitan area of Rio de Janeiro (MARJ). This work assessed the suitability and evaluation of the spatiotemporal distribution of Global Navigation Satellite Systems (GNSS) IWV from the cooperation of the International GNSS Monitoring and Assessment System (iGMAS) and the National Observatory (Observatório Nacional, ON) of Brazil, from the Brazilian Network for Continuous Monitoring (RBMC), and IWV products from Moderate Resolution Imaging Spectroradiometer (MODIS) and radiosonde, jointly with surface meteorological data, in two sectors of the state of Rio de Janeiro from February 2015–August 2018. High variability of the near surface air temperature (T) and relative humidity (RH) were observed among eight meteorological sites. The mean T differences between sites, up to 4.4 °C, led to mean differences as high as 3.1 K for weighted mean temperature (Tm) and hence 0.83 mm for IWV differences. Local grid points of MODIS IWV estimates had relatively good agreement with the GNSS-derived IWV, with mean differences from –2.4–1.1 mm for the daytime passages of the satellites TERRA and AQUA and underestimation from –9 mm to –3 mm during nighttime overpasses. A contrasting behavior was found in the radiosonde IWV estimates compared with the estimates from GNSS. There were dry biases of 1.4 mm (3.7% lower than expected) by radiosonde IWV during the daytime, considering that all other estimates were unbiased and the differences between IWVGNSS and IWVRADS were consistent. Based on the IWV comparisons between radiosonde and GNSS at nighttime, the atmosphere over the radiosonde site is about 1.2 mm and 2.3 mm wetter than that over the RBMC RIOD and iGMAS RDJN stations, respectively. The atmosphere over the site RIOD was 1.2 mm wetter than over that of RDJN for all three-hour means. These results showed that there were important variabilities in the meteorological conditions and in the distribution of water vapor in the MERJ. The data from the iGMAS RDJN station were feasible, together with those from the RBMC, MODIS, and radiosonde data, to investigate IWV in the region with occurrence of heat islands and peculiar physiographic and meteorological characteristics. This work recommends the magnification of the GNSS network in the state of Rio de Janeiro with the use of data from complete meteorological station collocated near every GNSS receiver, aiming to improve local IWV estimates and serving as additional support for operational numerical assimilation, weather forecast, and nowcast of extreme rainfall and flooding events.
Highlights
The development of satellite navigation systems has become an essential infrastructure for many countries, and not solely for military proposes
Field experiments and observations over long periods using Global Navigation Satellite Systems (GNSS) meteorology have been conducted in some places in the Subtropics and in the Tropics, such as the intensive campaigns in Amazonia to observe the evolution of deep convection by Adams et al [11,12,13,14] and the use of multisensors to intercompare integrated water vapor (IWV) estimates by Sapucci et al [15]
A robust control experiment could provide accurate explanations of the differences between ZTDRDJN and ZTDONRJ, whether they were primary related to instrumental errors or they were due to different receiver brand and model, hardware, phase center variations, strategies used, and/or multipath effect, such as those indicated in Jarlemark et al [60], King et al [61], and Ning et al [62,63]
Summary
The development of satellite navigation systems has become an essential infrastructure for many countries, and not solely for military proposes The advances in this area have received extensive documentation since the establishment of the Global Navigation Satellite Systems (GNSS) in the last decade of the 20th century. Several investigations have performed accurate measurements with high spatial and temporal resolution of water vapor in the troposphere, such as the studies using near real-time GPS sensing by Rocken et al [6], water vapor tomography with GPS network to improve moisture field forecast by Song et al [7], accurate multisensor estimates of water vapor [8], and validations of GNSS IWV against radiosonde and Moderate-Resolution Imaging Spectroradiometer (MODIS) data [9,10]. Field experiments and observations over long periods using GNSS meteorology have been conducted in some places in the Subtropics and in the Tropics, such as the intensive campaigns in Amazonia to observe the evolution of deep convection by Adams et al [11,12,13,14] and the use of multisensors to intercompare IWV estimates by Sapucci et al [15]
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