and Height 900 mb
Advection 850 mb
Advection 500 mb
700 mb
300 mb
Precipitation
The following fields are selected diagnostic fields for the October case. They include, frontogenesis, divergence at 700 and 300 mb, temperature advection at 850 mb and 500 mb and model derived precipitation. In addition to the figures, some interpretation and explanation of the fields are also provided.
| Field | 00UTC 17 Oct | 06UTC 17 Oct | 12UTC 17 Oct | 18UTC 17 Oct | 00UTC 18 Oct |
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| Frontogenesis and Height 900 mb |
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| Temperature Advection 850 mb |
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| Temperature Advection 500 mb |
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| Divergence 700 mb |
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| Divergence 300 mb |
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| Model Derived 12 Hour Precipitation |
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Other diagnostic fields can be found associated with the laboratory exercises.
In these figures the white contours are 900mb heights in meters, the dashed yellow contours are 900 mb temperature every 5C, and the shaded regions are Miller Frontogenesis using theta and the observed winds calculated at the 900 mb level. The field is scaled by 1e10 so that a value of 20 on the figure is 2e-9 K per 100 km per 3 hours.
At 00 UTC 17 Oct, the low level cold front emminates from the low at the border of Colorado and Kansas and extends westward across northern New Mexico and Arizona. The warm front extens northeastward from western Kansas across Iowa and northern Wisconsin. The strongest frontogenesis lies on the cold side of the fronts with the maximum at the Colorado, Nebraska and Kansas borders near the center of low pressure. By 06 UTC the low center has deepened somewhat and the frontogenesis continues to be strongest nearest the low. By 12 UTC, the low center has deepened significantly and the thermal pattern shows a classical shape with a strong gradient associated with the surface cold front and a less strong gradient associated with the warm front. Now the regions of strongest frontogenesis are in two separate areas, one with each front. In between these areas near the low over Iowa, the low level front is strong (the gradient of temperature is quite strong), however the frontogenesis here is weak indicating the the temperature gradient is not increasing with time.
By 18 UTC, the most active region of frontogenesis is associated with the warm front over northern Minnesota and Southern Ontario, whereas the cold front is not strengthening at this time. At 00 UTC 18 October, the low center is at it's deepest and the cold front has undergone some rejuvenation with the temperature gradient strengthening .
In these figures, the white contours are height (at either 850 mb or 500 mb) and the shaded regions are temperature advection in units of degrees K per second (K/s) times 1e5. The green/blue shades are cold advection and the red/yellow shades are warm advection.
At 00 UTC 17 October, the strongest low level temperature advections (cold and warm) are associated with the portion of the cold front over Kansas. The region of cold advection is especially strong. Further north over Minnesota, ahead of the warm front, there is weaker warm air advection. At the 500 mb level at this time, the temperature advections are weaker, but not insignificant. There is a substantial region of cold advection over Nebraska and Colorada and a region of warm advection over northern Minnesota. Casually examining the differential temperature advection between 850 and 500 mb reveals regions where one might expect height rises or falls (based on the geopotential tendency equation, eqn. 6.23 of Holton, 1992). Cold advection decreases with height modestly over western Nebraska and to a lesser extent over western Kansas. The heights are slightly lower in this region at 06 UTC (see 500 mb heights for 06 UTC 17 October). The region of decreasing warm advection with height is over northeastern Kansas. However, the heights remain unchanged most likely due to positive vorticity advection counteracting the differential warm advection.
At 06 UTC 17 October, the low level temperature advection remains strong behind the cold frontal zone and the warm advection has strengthened slightly over northeastern Minnesota. Again there are regions where differential temperature advection contributes to changes in geopotential height (e.g., decreasing heights over western Kansas and Oklahoma due to differential cold advection).
By 12 UTC 17 October, the storm is in it's most active development stage and the low level temperature advections are correspondingly strong. The upper level temperature advections have also increased and there is a broad area of cold advection associated with the deepening trough. By this time, it appears that the differential temperature advections are having less of an effect on the deepening of the trough.
At 18 UTC 17 October and 00 UTC 18 October, the storm is mature and the low level temperature advections remain quite strong immediately behind the cold front and north of the warm front. The temperature advection pattern at the upper levels is not as well structured with several areas of modest cold and warm advections.
In these figures, values of horizontal divergence (s^-1) times 1e5 are plotted where the blue positive values are regions of divergence and the yellow negative values are regions of convergence. The infrared satellite image is included in the figures of low level divergence (700 mb) in order to facilitate comparison of low level convergence and cloudiness.