Fig 4 - uploaded by Keith A. Brewster
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Maximum dual-Doppler crossing angles (color, degrees, scale at right) for the eight planned CASA Xband radar network (40 km range rings).
Context in source publication
Context 1
... the planned X-band network alone ( Figure 4 and the second column of or more radars, and 28% of the coverage area having coverage from three or more radars. 45% of the dual-Doppler area has 30° or better crossing angles allowing for excellent wind retrieval using dual-Doppler or 3DVAR methods. ...
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Citations
... Several regional analysis studies have combined 3DVAR with IAU [16][17][18][19][20][21]. [19] reported on an NWP experiment using 3DVAR with IAU applied to a heavy rainfall event. ...
... Furthermore, the length of the IAU time window should be adjusted, because a shorter time window can reduce the shock; therefore, the computa-tional cost will be lower, which is beneficial for real-time processing. In this study, the analysis increments were equally distributed in the IAU time window, but in [20], the analysis increments showed a time weighted distribution in the IAU time window. Therefore, the division method of analysis increments should also be adjusted. ...
... (18)(19)(20)(21) and second half (21-24 LST) of the period were lower, at 2.3 m s −1 and 2.9 m s −1 , respectively. ...
This study reports preliminary results from the three-dimensional variational method (3DVAR) with incremental analysis updates (IAU) of the surface wind field, which is suitable for real-time processing. In this study, 3DVAR with IAU was calculated for the case of a tornadic storm using 500-m horizontal grid spacing with updates every 10 min, for 6 h. Radial velocity observations by eight X-band multi-parameter Doppler radars and three Doppler lidars around the Tokyo Metropolitan area, Japan, were used for the analysis. In this study, three types of analyses were performed between 1800 to 2400 LST (local standard time: UTC + 9 h) 6 September 2015. The first used only 3DVAR (3DVAR), the second used 3DVAR with IAU (3DVAR+IAU), and the third analysis did not use data assimilation (CNTL). 3DVAR+IAU showed the best accuracy of the three analyses, and 3DVAR alone showed the worst accuracy, even though the background was updated every 10 min. Sharp spike signals were observed in the time series of wind speed at 10 m AGL, analyzed by 3DVAR, strongly suggesting that a “shock” was caused by dynamic imbalance due to the instantaneous addition of analysis increments to the background wind components. The spike signal was not shown in 3DVAR+IAU analysis, therefore, we suggest that the IAU method reduces the shock caused by the addition of analysis increments. This study provides useful information on the most suitable DA method for the real-time analysis of surface wind fields.
This paper describes tests of the recently developed
Incremental Analysis Updating with
Variable-Dependent Timing (IAU-VDT) assimilation
method that is now being used in the real-time
1-km grid scale NWP forecasts. The IAU-VDT allows the timing of the
introduction of analysis increments to differ for
each variable. Real time analysis and forecasting
products from the 26 Dec 2015 tornadoes in the
Dallas-Fort Worth metro area are presented as sample results.
