Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign

Abstract: In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ∼6.5 × 109 M ⊙. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87’s spectrum. We can exclude that the simultaneous γ-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the γ-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded

The 2015 Hurricane Season in the North Atlantic: An Analysis of Environmental Conditions

The 2015 North Atlantic hurricane season was particularly inactive, this inactivity occurring in the presence of a near-record El Niño, the strongest since 1997. When analyzing large-scale environmental conditions utilizing NCEP/NCAR Reanalysis 2, we show that the Caribbean was particularly inactive under very strong wind shear and positive Omega conditions. While conditions generally were not conducive in the North Atlantic, there were conducive conditions present at specific times and specific locations, and these tended to be when and where we saw tropical cyclone activity. Vorticity in particular showed large intraseasonal variability with the location of the positive vorticity relating to storms such as Ana in May, Claudette in July, multiple storms in August and September, and Joaquin in October. We assess how the active and inactive periods observed during the 2015 hurricane season were related to this month to month atmospheric variability

The 2015 Hurricane Season in the North Atlantic: An Analysis of Environmental Conditions

The 2015 North Atlantic hurricane season was particularly inactive, this inactivity occurring in the presence of a near-record El Niño, the strongest since 1997. When analyzing large-scale environmental conditions utilizing NCEP/NCAR Reanalysis 2, we show that the Caribbean was particularly inactive under very strong wind shear and positive Omega conditions. While conditions generally were not conducive in the North Atlantic, there were conducive conditions present at specific times and specific locations, and these tended to be when and where we saw tropical cyclone activity. Vorticity in particular showed large intraseasonal variability with the location of the positive vorticity relating to storms such as Ana in May, Claudette in July, multiple storms in August and September, and Joaquin in October. We assess how the active and inactive periods observed during the 2015 hurricane season were related to this month to month atmospheric variability

The 2016 North Atlantic Hurricane Season: A Season of Extremes

The 2016 North Atlantic hurricane season had an early start with a rare and powerful storm for January impacting the Azores at hurricane force. Likewise, the end of season heralded Otto which was record breaking in location and intensity being a high‐end Category 2 storm at landfall over southern central America in late November. We show that high precipitable water, positive relative vorticity, and low sea level pressure allowed for conducive conditions. During the season, few storms occurred in the main development region. While some environmental conditions were conducive for formation there (such as precipitable water, relative vorticity, and shear), the midlevel relative humidity was too low there for most of the season, presenting very dry conditions in that level of the atmosphere. We further find that the October peak in the accumulated cyclone energy was related to environmentally conducive conditions with positive relative humidity, precipitable water, relative humidity, and low values of sea level pressure. Overall 2016 was notable for a series of extremes, some rarely, and a few never before observed in the Atlantic basin, a potential harbinger of seasons to come in the face of ongoing global climate change

The 2009 Hurricane Season In the Eastern North Pacific Basin: An Analysis of Environmental Conditions

Despite the presence of an intensifying El Niño event, the 2009 eastern North Pacific hurricane season was near normal when considering overall hurricane activity. This is in contrast to the relative lull in activity observed between 1998 and 2008. Previous research has noted that the eastern North Pacific should be subdivided into two development regions, the western development region (WDR; 10°–20°N, 116°W–180°) and the eastern development region (EDR; 10°–20°N, North American coastline to 115.9°W), when examining interannual hurricane variability. In 2009, the EDR saw below average numbers of tropical cyclones of all intensities, while the WDR saw near-normal activity. However, activity in both regions varied sharply from month to month with periods of high activity in August and October and lower activity in July and September. This monthly variability was also observed in primary environmental forcing factors such as total precipitable water, tropospheric vertical wind shear, and low-level relative vorticity, particularly for the WDR. This variability was obscured by simply examining seasonal means. It is shown that for the 2009 season, large-scale environmental factors forced by the El Niño event and two cycles of the Madden–Julian oscillation contributed strongly to the observed patterns of cyclone activity across the basin

The Inactive 2009 Hurricane Season In the North Atlantic Basin: An Analysis of Environmental Conditions

The 2009 North Atlantic hurricane season was below normal when considering overall hurricane activity; however, activity was seen to vary sharply from month to month. All activity in 2009 occurred from August through early November with the highest activity in August, less activity in September and October, and only one tropical cyclone in November. Therefore, the 2009 hurricane season had a late start with no storms occurring in June and July. For the 2009 season, it is shown that large scale environmental factors forced by the El Niño event, such as increased vertical wind shear across the Caribbean and decreased mid-tropospheric relative humidity in the Main Development Region (10° N to 20° N and 20° W to 60° W), contributed strongly to the observed patterns of tropical cyclone activity across the basin. Lastly, the activity in the Atlantic in 2009 is compared to that in the Eastern North Pacific Western Development Region (10° N to 20° N and 116° W to 180°), and the potential for long-range seasonal forecasting of Atlantic tropical cyclones is noted