Nowcasting of tropical rain using dual frequency atmospheric brightness temperatures at Kolkata
01 Dec 2012-pp 1-4
TL;DR: In this article, the authors demonstrate that the use of brightness values of oxygen absorption lines in addition with the water vapor absorption lines can provide unique signature of heavy rain and demonstrate that using brightness values in combination with the oxygen absorption line can improve the performance of nowcasting of thunderstorm.
Abstract: Nowcasting of thunderstorm has important implication on minimizing the loss of properties and life Conventional approaches for such purpose using radiometer measured brightness temperature of only water vapor line usually tend to overestimate the occurrence probability In this paper, we demonstrate that use of brightness values of oxygen absorption lines in addition with the water vapor absorption lines can provide unique signature of heavy rain
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TL;DR: In this article, a microwave radiometer was used for nowcasting of heavy rain events at Kolkata (22.65°N, 88.45°E), a tropical location.
Abstract: Summary Nowcasting of heavy rain events using microwave radiometer has been carried out at Kolkata (22.65°N, 88.45°E), a tropical location. Microwave radiometer can produce the temperature and humidity profiles of the atmosphere with fairly good accuracy. Definite changes are observed in temperature and humidity profiles before and at the onset of heavy rain events. Concurrent changes in the brightness temperatures (BT) at 22 GHz and 58 GHz are found to be suitable to nowcast rain. The time derivatives of brightness temperatures at 22 GHz and 58 GHz are used as inputs to the proposed nowcasting model. In addition, the standard deviation of the product of these time derivatives is also considered. The model has been developed using the data of 2011 and validated for rain events of 2012–2013 showing a prediction efficiency of about 90% with alarm generated about 25 min in advance.
26 citations
Cites background from "Nowcasting of tropical rain using d..."
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TL;DR: In this article, a random forest based machine learning algorithm is tested for nowcasting of convective rain with a ground-based radiometer and the results indicate that the proposed model is very sensitive to the boundary layer instability as indicated by the variable importance measure.
Abstract: Automatic nowcasting of convective initiation and thunderstorms has potential applications in several sectors including aviation planning and disaster management. In this paper, random forest based machine learning algorithm is tested for nowcasting of convective rain with a ground based radiometer. Brightness temperatures measured at 14 frequencies (7 frequencies in 22–31 GHz band and 7 frequencies in 51–58 GHz bands) are utilized as the inputs of the model. The lower frequency band is associated to the water vapor absorption whereas the upper frequency band relates to the oxygen absorption and hence, provide information on the temperature and humidity of the atmosphere. Synthetic minority over-sampling technique is used to balance the data set and 10-fold cross validation is used to assess the performance of the model. Results indicate that random forest algorithm with fixed alarm generation time of 30 min and 60 min performs quite well (probability of detection of all types of weather condition ∼90%) with low false alarms. It is, however, also observed that reducing the alarm generation time improves the threat score significantly and also decreases false alarms. The proposed model is found to be very sensitive to the boundary layer instability as indicated by the variable importance measure. The study shows the suitability of a random forest algorithm for nowcasting application utilizing a large number of input parameters from diverse sources and can be utilized in other forecasting problems.
21 citations
References
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TL;DR: In this paper, the authors reviewed the status of forecasting convective precipitation for time periods less than a few hours (nowcasting), and developed techniques for nowcasting thunderstorm location were developed in the 1960s and 1970s by extrapolating radar echoes.
Abstract: This paper reviews the status of forecasting convective precipitation for time periods less than a few hours (nowcasting). Techniques for nowcasting thunderstorm location were developed in the 1960s and 1970s by extrapolating radar echoes. The accuracy of these forecasts generally decreases very rapidly during the first 30 min because of the very short lifetime of individual convective cells. Fortunately more organized features like squall lines and supercells can be successfully extrapolated for longer time periods. Physical processes that dictate the initiation and dissipation of convective storms are not necessarily observable in the past history of a particular echo development; rather, they are often controlled by boundary layer convergence features, environmental vertical wind shear, and buoyancy. Thus, successful forecasts of storm initiation depend on accurate specification of the initial thermodynamic and kinematic fields with particular attention to convergence lines. For these reasons ...
336 citations
"Nowcasting of tropical rain using d..." refers background in this paper
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TL;DR: In this article, a theory appears to be in place to predict humidity in the free troposphere if winds are known at large scales, providing a crucial link between small-scale behavior and large-scale mass and energy constraints.
Abstract: [1] Recent progress is reviewed in the understanding of convective interaction with water vapor and changes associated with water vapor in warmer climates. Progress includes new observing techniques (including isotopic methods) that are helping to illuminate moisture‐convection interaction, better observed humidity trends, new modeling approaches, and clearer expectations as to the hydrological consequences of increased specific humidity in a warmer climate. A theory appears to be in place to predict humidity in the free troposphere if winds are known at large scales, providing a crucial link between small‐scale behavior and large‐scale mass and energy constraints. This, along with observations, supports the anticipated water vapor feedback on climate, though key uncertainties remain connected to atmospheric dynamics and the hydrological consequences of a moister atmosphere. More work is called for to understand how circulations on all scales are governed and what role water vapor plays. Suggestions are given for future research.
334 citations
"Nowcasting of tropical rain using d..." refers background or methods in this paper
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TL;DR: In this article, a ground-based, 14-channel microwave radiometer (7 oxygen channels and 7 water vapour channels) has been in use at the Hong Kong International Airport since May 2008.
Abstract: Low-level windshear, which refers to sustained changes of headwind of 15 knots (7.7 m/s) or more over a distance of several hundred metres to about 4 km, could be hazardous to the aircraft flying close to the ground. This paper presents the preliminary results in the application of a radiometer in the alerting of lowlevel windshear. A ground-based, 14-channel microwave radiometer (7 oxygen channels and 7 water vapour channels) has been in use at the Hong Kong International Airport since May 2008. The radiometer data were mostly collected in clear and cloudy weather conditions without significant rainfall. Two approaches to the alerting of windshear have been studied, namely, the calculation of Brunt-Vaisala frequency and the standard deviation of the brightness temperature measured by a microwave radiometer at the 60 GHz oxygen absorption complex. The former tries to represent the stability of the boundary layer of the atmosphere (terrain-induced windshear tends to occur in stable boundary layer) and the latter tries to correlate the wind fluctuations with the temperature fluctuations. The performance of the windshear alerting rules so developed is studied by the relative operating characteristics (ROC) curve balancing the hit rate of pilot windshear reports and the alert duration. It turns out that the Brunt-Vaisala frequency does not show much skill in the alerting. On the other hand, the brightness temperature fluctuations are found to have skills in capturing the windshear. By combining the alerts from brightness temperature fluctuations with the existing alerts issued by the Doppler Light Detection And Ranging (LIDAR) system, it may be possible to fully automate the issuance windshear alerts for a runway corridor of the Hong Kong International Airport (HKIA) without the need of subjective windshear warnings issued by the aviation weather forecasters, at least for terrain-induced windshear. The probability of detection (POD) for pilot windshear report reaches 89 % with the percentage of time on alert of 20 %. The POD is only less than that for the existing overall windshear alerting service (machined generated windshear alerts plus windshear warnings issued by the aviation weather forecasters) by about 4 %.
25 citations
"Nowcasting of tropical rain using d..." refers background in this paper
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Journal Article•
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TL;DR: In this article, the predictability of precipitation occurrences and the estimation of rainfall intensity were investigated by using the brightness temperature (TB) of the ground-based microwave radiometers (MWR).
Abstract: Ground-based microwave radiometers (MWR) provide continuous thermodynamic (temperature, water vapor, and cloud liquid) soundings in the clear and cloudy weather conditions. These profiles can be determined by observing the intensity of the atmospheric radiation at selected frequencies. The MWR used in this study is TP/WVP-3000A, which measures the intensity of radiation at 8 water vapor channels (22-30 ㎓) and 14 oxygen channels (51-59 ㎓) to obtain thermodynamic profiles at National Center for Intensive Observation of severe weather (NCIO) located at Haenam, Korea. In this study, the predictability of precipitation occurrences and the estimation of rainfall intensity were investigated by using the brightness temperature (TB) of the MWR. The averaged differences of TBs in 2 hours before raining were calculated and compared with those of period unrelated with rain. In 2 hours before raining, the pronounced increase of TB was observed in water vapor channels (22-30 ㎓), while TBs in 54-59 ㎓ as oxygen channels were almost remaining constant except for the great increase of TB at 51-52 ㎓ related to cloud liquid water. Performance for forecasts of precipitation occurrences using the preceding increases of TBs at 22.2 ㎓, 30.0 ㎓, and 51.2 ㎓ was improved and better than the 3-hour operational (routine) forecasts. The estimation of rainfall intensity was examined by two simple estimative methods using the linear and the nonlinear regression analyses between rainfall intensity and TBs. Rainfall intensity was estimated by the calculated regression curves of TBs from MWR and compared with observed one by an Optical Rain Gauge (ORG) at the Haenam NCIO. As a result of the verification on forecasting performances, both the linear and the logarithmic regression methods between the observed and the estimated rainfall intensity showed substantially high in Equitable Threat Scores (ETSs) and correlation coefficients.
23 citations
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