Time filter

Source Type

Flora Vista, NM, United States

Kahler S.W.,Air Force Research Lab | Ling A.,Atmospheric Environmental Research
Space Weather | Year: 2015

The forecasting of solar energetic particle (SEP) event probabilities at Earth has been based primarily on the estimates of magnetic free energy in active regions and on the observations of peak fluxes and fluences of large (≥ M2) solar X-ray flares. These forecasts are typically issued for the next 24 h or with no definite expiration time, which can be deficient for time-critical operations when no SEP event appears following a large X-ray flare. It is therefore important to decrease the event probability forecast with time as a SEP event fails to appear. We use the NOAA listing of major (≥10 pfu) SEP events from 1976 to 2014 to plot the delay times from X-ray peaks to SEP threshold onsets as a function of solar source longitude. An algorithm is derived to decrease the SEP event probabilities with time when no event is observed to reach the 10 pfu threshold. In addition, we use known SEP event size distributions to modify probability forecasts when SEP intensity increases occur below the 10 pfu event threshold. An algorithm to provide a dynamic SEP event forecast, Pd, for both situations of SEP intensities following a large flare is derived. ©2015. American Geophysical Union. All Rights Reserved. Source

Cliver E.W.,Air Force Research Lab | Ling A.G.,Atmospheric Environmental Research | Belov A.,IZMIRAN | Yashiro S.,NASA | Yashiro S.,Catholic University of America
Astrophysical Journal Letters | Year: 2012

We suggest that the flatter size distribution of solar energetic proton (SEP) events relative to that of flare soft X-ray (SXR) events is primarily due to the fact that SEP flares are an energetic subset of all flares. Flares associated with gradual SEP events are characteristically accompanied by fast (≥1000kms-1) coronal mass ejections (CMEs) that drive coronal/interplanetary shock waves. For the 1996-2005 interval, the slopes (α values) of power-law size distributions of the peak 1-8 Å fluxes of SXR flares associated with (a) >10MeV SEP events (with peak fluxes ≥1prcm-2s-1sr-1) and (b) fast CMEs were 1.3-1.4 compared to 1.2 for the peak proton fluxes of >10MeV SEP events and 2 for the peak 1-8 Å fluxes of all SXR flares. The difference of 0.15 between the slopes of the distributions of SEP events and SEP SXR flares is consistent with the observed variation of SEP event peak flux with SXR peak flux. © 2012 The American Astronomical Society. All rights reserved. Source

Cliver E.W.,Air Force Research Lab | Tylka A.J.,NASA | Dietrich W.F.,Praxis Inc. | Ling A.G.,Atmospheric Environmental Research
Astrophysical Journal | Year: 2014

We explore requirements for a solar particle event (SPE) and flare capable of producing the cosmogenic nuclide event of 775 A.D., and review solar circumstances at that time. A solar source for 775 would require a >1 GV spectrum ∼45 times stronger than that of the intense high-energy SPE of 1956 February 23. This implies a >30 MeV proton fluence (F30) of ∼8 × 1010 proton cm-2, ∼10 times larger than that of the strongest 3 month interval of SPE activity in the modern era. This inferred F30 value for the 775 SPE is inconsistent with the occurrence probability distribution for >30 MeV solar proton events. The best guess value for the soft X-ray classification (total energy) of an associated flare is ∼X230 (∼9 × 1033 erg). For comparison, the flares on 2003 November 4 and 1859 September 1 had observed/inferred values of ∼X35 (∼1033 erg) and ∼X45 (∼2 × 1033 erg), respectively. The estimated size of the source active region for a ∼1034 erg flare is ∼2.5 times that of the largest region yet recorded. The 775 event occurred during a period of relatively low solar activity, with a peak smoothed amplitude about half that of the second half of the 20th century. The ∼1945-1995 interval, the most active of the last ∼2000 yr, failed to witness a SPE comparable to that required for the proposed solar event in 775. These considerations challenge a recent suggestion that the 775 event is likely of solar origin. © 2014. The American Astronomical Society. All rights reserved. Source

Cliver E.W.,Air Force Research Lab | Petrie G.J.D.,U.S. National Solar Observatory | Ling A.G.,Atmospheric Environmental Research
Astrophysical Journal | Year: 2012

We compared time profiles of changes of the unsigned photospheric magnetic flux in active regions with those of their associated soft X-ray (SXR) bursts for a sample of 75 ≥ M5 flares well observed by Global Oscillation Network Group longitudinal magnetographs. Sixty-six of these events had stepwise changes in the spatially integrated unsigned flux during the SXR flares. In superposed epoch plots for these 66 events, there is a sharp increase in the unsigned magnetic flux coincident with the onset of the flare impulsive phase while the end of the stepwise change corresponds to the time of peak SXR emission. We substantiated this result with a histogram-based comparison of the timing of flux steps (onset, midpoint of step, and end) for representative points in the flaring regions with their associated SXR event time markers (flare onset, onset of impulsive phase, time of peak logarithmic derivative, maximum). On an individual event basis, the principal part of the stepwise magnetic flux change occurred during the main rise phase of the SXR burst (impulsive phase onset to SXR peak) for 60% of the 66 cases. We find a close timing agreement between magnetic flux steps and >100keV emission for the three largest hard X-ray (>100keV) bursts in our sample. These results identify the abrupt changes in photospheric magnetic fields as an impulsive phase phenomenon and indicate that the coronal magnetic field changes that drive flares are rapidly transmitted to the photosphere. © 2012. The American Astronomical Society. All rights reserved. Source

Wecht K.J.,Harvard University | Jacob D.J.,Harvard University | Wofsy S.C.,Harvard University | Kort E.A.,Harvard University | And 6 more authors.
Atmospheric Chemistry and Physics | Year: 2012

We validate satellite methane observations from the Tropospheric Emission Spectrometer (TES) with 151 aircraft vertical profiles over the Pacific from the HIAPER Pole-to-Pole Observation (HIPPO) program. We find that a collocation window of ±750 km and ±24 h does not introduce significant error in comparing TES and aircraft profiles. We validate both the TES standard product (V004) and an experimental product with two pieces of information in the vertical (V005). We determine a V004 mean bias of 65.8 ppb and random instrument error of 43.3 ppb. For V005 we determine a mean bias of 42.3 ppb and random instrument error of 26.5 ppb in the upper troposphere, and mean biases (random instrument errors) in the lower troposphere of 28.8 (28.7) and 16.9 (28.9) ppb at high and low latitudes respectively. Even when V005 cannot retrieve two pieces of information it still performs better than V004. An observation system simulation experiment (OSSE) with the GEOS-Chem chemical transport model (CTM) and its adjoint shows that TES V004 has only limited value for constraining methane sources. Our successful validation of V005 encourages its production as a standard retrieval to replace V004. © 2012 Author(s). Source

Discover hidden collaborations