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Global (1 dB ABS) 
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North Polar (10 dB ABS) 
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South Polar (10 dB ABS) 
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Global 5 MHz 
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North Polar 5 MHz 
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South Polar 5 MHz 
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Global 10 MHz 
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North Polar 10 MHz 
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South Polar 10 MHz 
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Global 15 MHz 
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North Polar 15 MHz 
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South Polar 15 MHz 
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Global 20 MHz 
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North Polar 20 MHz 
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South Polar 20 MHz 
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Global 25 MHz 
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North Polar 25 MHz 
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South Polar 25 MHz 
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Global 30 MHz 
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North Polar 30 MHz 
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South Polar 30 MHz 
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The D-Region Absorption Product addresses the operational impact of the solar X-ray flux and SEP events on HF radio communication. Long-range communications using high frequency (HF) radio waves (3 - 30 MHz) depend on reflection of the signals in the ionosphere. Radio waves are typically reflected near the peak of the F2 layer (~300 km altitude), but along the path to the F2 peak and back the radio wave signal suffers attenuation due to absorption by the intervening ionosphere.
The D-Region Absorption Prediction model is used as guidance to understand the HF radio degradation and blackouts this can cause.
Conditions in the D-region of the ionosphere have a dramatic effect on high frequency (HF) communications and low frequency (LF) navigation systems. The global D-Region Absorption Predictions (D-RAP) depicts the D-region at high latitudes where it is driven by particles as well as low latitudes, where photons cause the prompt changes. This product merges all latitudes using appropriate displays, and is useful to customers from a broad base that includes emergency management, aviation and maritime users.
The D-Region Absorption Map is composed of four dynamic components: a global map of the highest frequency affected by absorption of 1 dB due to either solar X-ray flux or SEP events or a combination of both, an attenuation bar graph, status messages, and an estimated recovery clock. All of the components update continuously, driven by one-minute GOES X-ray flux data and by five-minute GOES proton flux data. To complement the global frequency map, polar projection maps of the highest frequency affected by absorption of 10 dB due to primarily to SEP events are also available by clicking on the North Pole and South Pole links. The Tabular Values link displays numeric values of the frequency map in 5-degree latitude and 15-degree longitude increments. A more complete discussion of the product can be found in the Global D-Region Absorption Prediction documentation.
D-Region Absorption Prediction, Release 2 (D-RAP) was transitioned into operations at SWPC in 2009. This release added the effect of energetic protons on radio waves propagating through the ionosphere's D-region (50 - 90 km). Release 1 included only the effects of solar X-Ray flares. Both effects are based on empirical relationships. A Model Validation report for Release 2 is available at: https://www.ngdc.noaa.gov/stp/drap/DRAP-V-Report1.pdf. Improvements to the web page presentation, bringing-it to the present form, were implemented in May 2011.
Current numerical data can be downloaded in ASCII text format at:
https://services.swpc.noaa.gov/text/drap_global_frequencies.txt
Archived data can be accessed at: https://www.ngdc.noaa.gov/stp/drap/index.html