Precipitable water plume in the Gulf of Mexico

April 7th, 2008 |

GOES-12 10.7µm IR image

An AWIPS image of the GOES-12 10.7 µm “IR window” channel (above) showed a large cluster of convection that developed in the vicinity an inverted surface trough axis over the Gulf of Mexico on 07 April 2008.

GOES-12 6.5 µm water vapor images (Animated GIF)

An animation of AWIPS images of the GOES-12 6.5 µm “water vapor channel” (above) suggested that much of the middle to upper troposphere was quite dry (yellow to orange colors) over the Gulf of Mexico region on that particular day.

POES AMSU total precipitable water (Animated GIF)

However, AWIPS images of the POES AMSU total precipitable water (above) and the DMSP SSM/I total precipitable water (below) revealed that a plume of significant moisture was moving northward into the central Gulf of Mexico during 06-07 April, providing a necessary ingredient for the development of the convection.

DMSP SSM/I total precipitable water (Animated GIF)

A comparison of the GOES water vapor channel image with total precipitable water products from the GOES sounder, POES AMSU, and DMSP SSM/I (below) demonstrates how misleading it would be to simply interpret the GOES vapor image alone and conclude that the entire Gulf of Mexico region was generally “very dry” (aside from the cluster of convection that had developed). The bulk of the precipitable water plume existed at lower levels of the atmosphere, below the layer that was being sensed by the GOES imager water vapor channel (which, according to the GOES water vapor weighting function plot for Brownsville, Texas at 12 UTC on 07 April was centered around 500 hPa).

GOES + POES imagery (Animated GIF)

An animation of hourly composites of the CIMSS MIMIC total precipitable water product (below) showed the evolution of the moist plume as it emerged into the southwestern Gulf of Mexico and then moved northeastward into the central Gulf during the 06-07 April period. The MIMIC product blends microwave total precipitable water data from the DMSP SSM/I and the Aqua AMSR-E polar orbiting instruments, and advects the blended moisture fields using lower-tropospheric mean layer wind derived from the GFS model.

MIMIC total precipitable water (Animated GIF)

Convergence of the Brazil Current and the Malvinas/Falkland Current

April 7th, 2008 |

AVHRR sea surface temperature (Google Maps)

[Hat-tip to Amato Evan at CIMSS for pointing out this very interesting AVHRR sea surface temperature imagery] AVHRR sea surface temperature (SST) data (above, viewed using Google Earth) revealed the striking convergence of the Brazil Current and the Malvinas/Falkland Current off the east coast of South America on 07 April 2008. The Brazil Current transports warm subtropical water (SST values of 22º to 28ºC, yellow to orange colors) southward, while the Malvinas/Falkland Current transports cold Antarctic water (SST values of 6º to 12ºC, cyan to dark blue colors) northward. These two ocean currents are seen to converge several hundred kilometers off the coast of Argentina — the exact location of this Brazil/Malvinas convergence zone changes with the seasons.

An animation of daily AVHRR SST images from 01 to 07 April (below) shows subtle variations in the position of the Brazil and Malvinas ocean currents, as well as interesting eddy structures in the vicinity of the Brazil-Malvinas Confluence. Note the appearance of a well-defined “comma cloud” associated with a strong cyclone off the coast on 06 April (recall that winds flow clockwise around a cyclone in the Southern Hemisphere).

AVHRR sea surface temperature images (Animated GIF)

The colder waters of the Malvinas Current are rich in nutrients which support the growth of marine plant life, which then attracts large numbers of fish to feed — therefore, the commercial fishing industry is very interested in satellite data that accurately depict the location of such cold ocean currents.

Reference: Convergence Zones – Where the Action Is (NASA Goddard Space Flight Center)