Space Weather Prediction Center

National Oceanic and Atmospheric Administration

D Region Absorption Predictions (D-RAP)

Global (1 dB ABS)

thumbnail of global absorption predictions at 1 dB

North Polar (10 dB ABS)

thumbnail of North global absorption predictions at 10 dB

South Polar (10 dB ABS)

thumbnail of South global absorption predictions at 10 dB

Global 5 MHz

thumbnail of global absorption predictions at 5 MHz

North Polar 5 MHz

thumbnail of North polar global absorption predictions at 5 MHz

South Polar 5 MHz

thumbnail of South polar global absorption predictions at 5 MHz

Global 10 MHz

thumbnail of global absorption predictions at 10 MHz

North Polar 10 MHz

thumbnail of North polar global absorption predictions at 10 MHz

South Polar 10 MHz

thumbnail of South polar global absorption predictions at 10 MHz

Global 15 MHz

thumbnail of global absorption predictions at 15 MHz

North Polar 15 MHz

thumbnail of North polar global absorption predictions at 15 MHz

South Polar 15 MHz

thumbnail of South polar global absorption predictions at 15 MHz

Global 20 MHz

thumbnail of global absorption predictions at 20 MHz

North Polar 20 MHz

thumbnail of North polar global absorption predictions at 20 MHz

South Polar 20 MHz

thumbnail of South polar global absorption predictions at 20 MHz

Global 25 MHz

thumbnail of global absorption predictions at 25 MHz

North Polar 25 MHz

thumbnail of North polar global absorption predictions at 25 MHz

South Polar 25 MHz

thumbnail of South polar global absorption predictions at 25 MHz

Global 30 MHz

thumbnail of global absorption predictions at 30 MHz

North Polar 30 MHz

thumbnail of North polar global absorption predictions at 30 MHz

South Polar 30 MHz

thumbnail of South polar global absorption predictions at 30 MHz

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.

HF Radio Communications

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