New RTS Weather Station Web Site Products
By Brian Morrison, ATSC Senior Systems Scientist
August 5, 2009
Over the last few months we have added three new products to the RTS Weather Station web site. Here is a brief description of each one:
1. Kwajalein All-Sky Video
A vertically pointing All-Sky Video camera system was installed at the Kwajalein Weather Station in November of 2008 to support our Distributed Operations. This is a system custom-built by ATSC and is based on an original design by T.E. Pickering at the Multiple Mirror Telescope (MMT) Observatory in Tucson, Arizona (http://skycam.mmto.arizona.edu). This is a unique, relatively low-cost, system which uses an amateur astronomy CCD video imaging camera and an auto-iris fish-eye lens to allow safe operations in all lighting conditions, even direct sunlight. Software is used to automatically adjust imaging and exposure characteristics at night based on mean image pixel values to provide useful cloud images. At night when skies are relatively clear you may see many small white specks - those that are moving are stars or planets, the ones that are not are due to noise in the CCD because of our warm environment. Pictures are produced approximately every minute. When displayed as an animated sequence of images, cloud motions, types, and their evolution can often be discerned. A one-hour sequence of images can be seen on our web site and this is updated approximately every 15 minutes. A small rod at the top of each image is aligned towards the north, so any clouds moving from the top to the bottom are coming out of the north. Because the camera looks directly up, east and west appear reversed: east is on the left side of each image and west is on the right. So, any clouds moving from left to right are coming out of the east. When there are multiple cloud layers overhead, interpretation can be complicated. But, that is part of the fun in watching the animations! See the latest image here.
2. Seven-day Time Series of Weather Radar Activity
The Kwajalein Polarimetric S-band Weather Radar (KPOL) continuously monitors the location and development of precipitating weather systems around Kwajalein 24 hours a day. On fair weather days, there is generally little activity and the coverage of precipitation “echoes” in the area monitored by the radar is small. Conversely, on very active and rainy days, this coverage can be significant. Kwajalein Weather Station meteorologists sometimes find it helpful to look at a time series of this echo coverage over several days to look for sudden changes in the overall weather pattern and diurnal (day vs night) patterns. The 7-day time series on our web site is updated approximately every 20 minutes. The echo coverage is derived from a 1-km altitude Constant Altitude Plan Position Indicator (CAPPI) radar product and only echoes within a 100-km box centered on Kwajalein are counted. The green line shows the approximate coverage of echoes within this box that represent generally light intensity rainfall, while the red line includes all echoes detected on the radar from light to heavy rainfall. The y-axis on the plot is the percentage of echo coverage within the 100-km box and its scale will change depending upon the maximum coverage value over the entire 7-day time series. See the latest image here.
3. MTSAT Hovmöller Plot
Hovmöller diagrams are a classical way of plotting meteorological time series data to highlight the role of waves in the atmosphere. The axes of a Hovmöller diagram are usually longitude along the x-axis, time along the y-axis, and then the value of a meteorological field shown as a contour plot. This provides a useful way to view time varying phenomena at a given latitude. It is particularly useful in the deep oceanic tropics where disturbances at low latitudes often move from east to west in the tropical easterly wind flow. Because of the lack of "conventional" meteorological data over much of the Pacific Ocean, we are highly dependent upon satellite data to identify and track the weak disturbances that develop, move, and decay in the tropics. We use geostationary and polar orbiting meteorological satellite data at the RTS Weather Station in many different ways, and can manipulate and combine them with other data using our Man-computer Interactive Data Access System (McIDAS) developed at the University of Wisconsin Space Sciences and Engineering Center. In our Hovmöller plots, we use McIDAS to put 6 strips of visible wavelength satellite imagery from the Japanese MTSAT-1R satellite between 4 and 12N latitude every 24 hours together in a running 6-day series. This can be a useful tool to identify and track some disturbances in the tropical easterly flow as they approach and move through the Marshall Islands. We update this product once a day every afternoon. See the latest plot here.