Climatologies of nighttime upper thermospheric winds measured by ground‐based Fabry‐Perot interferometers during geomagnetically quiet conditions: 1. Local time, latitudinal, seasonal, and solar cycle dependence

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94633/1/jgra18559.pd

DWM07 global empirical model of upper thermospheric storm-induced disturbance winds

We present a global empirical disturbance wind model (DWM07) that represents average geospace-storm-induced perturbations of upper thermospheric (200-600 km altitude) neutral winds. DWM07 depends on the following three parameters: magnetic latitude, magnetic local time, and the 3-h Kp geomagnetic activity index. The latitude and local time dependences are represented by vector spherical harmonic functions ( up to degree 10 in latitude and order 3 in local time), and the Kp dependence is represented by quadratic B-splines. DWM07 is the storm time thermospheric component of the new Horizontal Wind Model (HWM07), which is described in a companion paper. DWM07 is based on data from the Wind Imaging Interferometer on board the Upper Atmosphere Research Satellite, the Wind and Temperature Spectrometer on board Dynamics Explorer 2, and seven ground-based Fabry-Perot interferometers. The perturbation winds derived from the three data sets are in good mutual agreement under most conditions, and the model captures most of the climatological variations evident in the data

An empirical model of the Earth's horizontal wind fields: HWM07

The new Horizontal Wind Model (HWM07) provides a statistical representation of the horizontal wind fields of the Earth's atmosphere from the ground to the exosphere (0-500 km). It represents over 50 years of satellite, rocket, and ground-based wind measurements via a compact Fortran 90 subroutine. The computer model is a function of geographic location, altitude, day of the year, solar local time, and geomagnetic activity. It includes representations of the zonal mean circulation, stationary planetary waves, migrating tides, and the seasonal modulation thereof. HWM07 is composed of two components, a quiet time component for the background state described in this paper and a geomagnetic storm time component (DWM07) described in a companion paper

Organic matter from Artic sea ice loss alters bacterial community structure and function

Continuing losses of multi-year sea ice (MYI) across the Arctic are resulting in first-year ice (FYI) dominating the Arctic ice pack. Melting FYI provides a strong seasonal pulse of dissolved organic matter (DOM) into surface waters; however, the biological impact of this DOM input is unknown. Here we show that DOM additions cause significant and contrasting changes in under-ice bacterioplankton abundance, production and species composition. Utilization of DOM was influenced by molecular size, with 10-100 kDa and >100 kDa DOM fractions promoting rapid growth of particular taxa, while uptake of sulfur and nitrogen-rich low molecular weight organic compounds shifted bacterial community composition. These results demonstrate the ecological impacts of DOM released from melting FYI, with wideranging consequences for the cycling of organic matter across regions of the Arctic Ocean transitioning from multi-year to seasonal sea ice as the climate continues to warm

Climatology and storm time dependence ofnighttime thermospheric neutral winds over Millstone Hill

We use 630.0 nm nightglow Fabry-Perot measurements over Millstone Hill from 1989–1999 to study the climatology and storm time dependence of the midlatitude thermospheric winds. Our quiet time wind patterns are consistent with results from earlier studies. We determine the perturbation winds by subtracting from each measurement the corresponding quiet time averages. The climatological zonal disturbance winds are largely independent of season and solar flux and show large early night westward and small late-night eastward winds similar to disturbance ion drifts. The meridional perturbation winds vary strongly with season and solar flux. When the solar flux is low, the winter and equinox average meridional winds change from equatorward to poleward at ∼2200 LT, and the summer winds are equatorward throughout the night. The high solar flux meridional winds are poleward, with magnitudes increasing from dawn to dusk at all seasons. These disturbance winds patterns are in poor agreement with results from the empirical horizontal wind model, HWM-93. The zonal and meridional disturbance winds show very large variations relative to their average values. We have also studied the time-dependent response of the midlatitude thermospheric winds to enhanced magnetic activity. The early night westward winds build up to large amplitudes (about twice their climatological values) in ∼6 hours; the late-night eastward winds are smaller and reach their peak values ∼3 hours after the increase in magnetic activity. The storm time dependence of the meridional winds is considerably more complex than that of the zonal winds, and it varies with season and solar flux. Following enhanced magnetic activity, equatorward winds are observed at all local times and seasons, but the increase of their amplitudes with storm time is fastest in the late local time sector. Near midnight, and when the solar flux is low, the meridional winds reverse from equatorward to poleward ∼6–10 hours after the increase in magnetic activity. This reversal is fastest (slowest) during December (June) solstice. At later local times, and for high solar flux conditions, the variation of the meridional disturbance winds is season independent. The observed storm time dependence partly explains the large variability of the disturbance winds

Climatology and latitudinal gradients of quiet-timethermospheric neutral winds over Millstone Hill from Fabry-Perot interferometermeasurements

Midlatitude nighttime thermospheric neutral winds are strongly dependent on season, solar activity, and latitude. We use an extensive database of wind measurements made during 1989–2001 by the Millstone Hill Fabry-Perot interferometer to study the detailed climatology of quiet time neutral winds near an altitude of 250 km. To facilitate the analysis of these data, we develop a local time, day-of-year, solar flux, and latitude-dependent empirical model, with the latitude dependence obtained by considering north looking and south looking observations separately. Our results show that the zonal winds are predominantly eastward after dusk and westward before dawn, with the strongest eastward winds occurring in the winter and with an east-to-west transition that occurs earliest in the summer. The zonal winds exhibit weak-to-moderate latitudinal gradients, with more westward values to the north. The zonal wind magnitudes decrease with increasing solar flux; the strongest trends occur during winter. The meridional winds are predominantly equatorward in all cases and exhibit strong latitudinal gradients, with larger values to the north. The maximum nighttime equatorward winds decrease with increasing solar flux, except during summer, when there is no significant solar activity variation. They are largest during the summer, except at solar minimum when a semiannual variation is observed and the peak winds occur during the equinoxes. Earlier studies of midlatitude wind measurements are generally consistent with our data, with our results providing a considerably more detailed description of the nighttime wind climatology at midlatitudes

Climatologies of nighttime upper thermospheric winds measured by ground-based Fabry-Perot interferometers during geomagnetically quiet conditions: 2. High-latitude circulation and interplanetary magnetic field dependence

We analyze upper thermospheric (∼250 km) nighttime horizontal neutral wind patterns, during geomagnetically quiet (Kp < 3) conditions, over the following locations: South Pole (90°S), Halley (76°S, 27°W), Millstone Hill (43°N, 72°W), Søndre Strømfjord (67°N, 51°W), and Thule (77°N, 68°W). We examine the wind patterns as a function of magnetic local time and latitude, solar cycle, day of year, and the dawn-dusk and north-south components of the interplanetary magnetic field (IMF B y and B z ). In magnetic coordinates, the quiet time high-latitude wind patterns are dominated by antisunward flow over the polar cap, with wind speeds that generally increase with increasing solar extreme ultraviolet (EUV) irradiation. The winds are generally stronger during equinox than during winter, particularly over the South Pole in the direction of eastern longitudes. IMF B y exerts a strong influence on the wind patterns, particularly in the midnight sector. During winter, B y positive winds around midnight in the northern (southern) hemisphere are directed more toward the dusk (dawn) sector, compared to corresponding B y negative winds; this behavior is consistent with the B y -dependence of statistical ionospheric convection patterns. The strength of the wind response to B y tends to increase with increasing solar EUV irradiation, roughly in proportion to the increased wind speeds. Quiet time B y effects are detectable at latitudes as low as that of Millstone Hill (magnetic latitude 53°N). Quiet time B z effects are negligible except over the magnetic polar cap station of Thule