El Niño and Length of Day

This figure shows Length of Day (LOD) determined from VLBI measurements after removing a) tidal terms; b) seasonal terms and c) long-term drift and compares the LOD with the monthly El Niño-Southern Oscillation Index. The effect of El Niño is clearly visible in the LOD. During an El Niño, the solid Earth slows down, and the days get longer as more angular momentum goes into the atmosphere. The effect is small, with a maximum slow down of 800 microseconds/day.

VLBI2010 Simulations

The GSFC VLBI group has done simulations for a 32-site network and then for a sequence of subset networks of 24, 16, and 8 sites. Figure 1 below shows the 32-site network along with the 8-site network subset. Figure 2 shows that Earth Orientation Parameter (X-pole, Y-pole, and UT1) precision generally improves with increasing network size. (The decrease in UT1 precision for the 24-site network needs more investigation, but it is believed to be caused by the observation scheduling algorithm and the particular choice of 8 additional site locations relative to the 16-site network locations.) Precision is plotted relative to the 8-site network precision. The plot shows that there is about a factor of two improvement in going from 8 sites to 32 sites.

Source Monitoring Project

VLBI observes radio signals from quasars ("sources"). Since the start of February, 2004, 302 sources have been observed more frequently as part of an effort to build a history of observations so that source quality can be monitored. This graph demonstrates the success of the effort. It shows the number of sources which have been observed in zero sessions (red line), one session (blue line) or two or more sessions (green line). Over time, as more sources are observed, the number of sources in the red and blue categories drop as sources move into the green category. This graph shows data from September 2003 through July 2005, but the monitoring effort is still continuing.

UT1 Uncertainty Improvement

Global Site Velocities

The arrows show the total motion of the Earth at selected VLBI observing sites. The total motion at a site is the motion of the underlying plate added to the motion at the site itself. The reference frame is the NUVEL1A-NNR (No-Net-Rotation) frame. The jagged lines mark the boundaries between plates. The Earth deforms at boundaries where plates are moving in different directions (such as the United States' west coast, Alaska and Japan). Please note that this plot covers 360 degrees of longitude, so the left and right edges of the plot are actually next to each other, and the two Antarctica sites are moving towards each other.

Mutual Visibility

This plot shows the mutual visibility of Kokee (green curve on the left), NyAlesund (red curve in the center) and Wettzell (purple curve on the right). Sources are plotted as squares. A source must be inside the curve corresponding to a station to be visible at that station. VLBI observations require that a source be visible at two or more stations simultaneously. It is interesting to note that all of the sources which are simultaneously observable by Kokee and Wettzell are also observable by NyAlesund.

The projection is an equal area projection of the whole sky, centered on the North Pole. The concentric rings are lines of constant declination, ranging from 60 degrees north (the innermost circle) to 90 degrees south (the outermost circle). This circle corresponds to the single point at the South Pole. Source positions are for a particular epoch. Sources rotate around the North Pole once per sidereal day.