2-9 July 1999 -- GOES TPW & LI

Atmospheric Moisture and Stability 2-9 July 1999 - Southwest Monsoon

Bob Rabin

NOAA/NSSL

and

CIMSS/Univ. Wisconsin-Madison

Animations of hourly Total Precipitable Water (TPW) and Lifted Index (LI), a measure of atmospheric stability, derived from GOES-8/10 sounder retrievals (Menzel et al., 1998) can be viewed by clicking on the desired day in the table below. The time period captures several convective systems east of the Rocky Mountains and the onset of monsoon conditions in the southwest U.S. Storms over southern Nevada produced flash flooding in the Las Vegas area on 8-9 July. The animations can be used to help visualize the source region for moisture and instability in relation to the Gulf of California.. In regard to the LI, it should be noted that negative values indicate conditional instability given that there is a forcing mechanism to initially lift air parcels to their 'level of free convection'. The amount of instability is inversely related to the value of the LI. Positive values indicate the lack of convective instability. Generally, the LI is inversely related to TPW. However unlike TPW, the LI has a distinct diurnal trend as it is linked to the temperature profile in the lower atmosphere. The images of TPW and LI were obtained from archives of real-time products at the Cooperative Institute for Meteorological Satellite Studies ( CIMSS ) at the University of Wisconsin-Madison.

To view hourly animations per day, just click on the X for the desired parameter and time in Table 1.

Table 1

Date	2 July	3 July	4 July	5 July	6 July	7 July	8 July	9 July
TPW	X	X	X	X	X	X	X	X
LI	X	X	X	X	X	X	X	X

The animations use a Java Applet written by Tom Whittaker at the Cooperative Institute for Meteorological Satellite Studies ( CIMSS ) at the University of Wisconsin-Madison.

To view an animation of TPW for the entire period (at 6 hr intervals) click here . If loading this loop is too long, it is possible to view animations for each half of this period: 2-5 July and 6-9 July .

To view animations of TPW with overlays from the ETA model, choose 2-5 July or 6-9 July . Note that each of these loops require 48 images to be downloaded which may take considerable time and requires sufficient computer memory. You can select overlays of geopotential height fields at 500 and 850 mb by clicking on the appropriate boxes. These are from model analyses at 00 and 12 UTC, and 6 hour forecasts at 06 and 18 UTC. (Heights are in geopotential meters above sea level and may be lower than the surface in mountanous areas). The contours in these overlays give an approximate direction of air flow at the mid and lower altitudes above the ground. At 500 mb, the flow is roughly along contours and from right to left when pointing from low to high geopotential height. At 850 mb, there can be an additional component of the flow from high to low heights. The flow at 850 mb may also vary on a small scale due to terrain and atmospheric features poorly resolved in the model.

To view an animation of Sea Surface Temperature (SST) for the entire period (at 3 hr intervals) click here . If loading this loop is too long, it is possible to view animations for each half of the period: 2-5 July and 6-9 July . These images show 3-hr averages of SST estimated from hourly GOES-10 data. Estimates were obtained from X. Wu at the CIMSS using the multi-spectral technique of Wu et al., (1999). Convective cloud cover is overlayed on the SST images for comparison purposes.

To view animations of SST with overlays from the ETA model, choose 2-5 July or 6-9 July .

A comparison between the SST, TPW and LI fields can be viewed using the "fade" functionality of Tom Whittaker's Java Applet. Images at 21 UTC are chosen because of their relative lack of cloud cover. After clicking on the desired day in Table 2, the comparison can be achieved by moving the slider with the mouse to fade between SST, TPW, and LI.

Table 2

Date	2 July	3 July	4 July	5 July	6 July	7 July	8 July	9 July
Fader	X	X	X	X	X	X	X	X

A comparison of GOES sounder and ETA model TPW are available from Table 3. Images are shown at 6 hour intervals. Note that model fields at 00 and 12 UTC are from the ETA analysis (0 hr forecast), 06 and 18 UTC images are from 6 hour forecasts made at 00 and 12 UTC respectively.

Table 3

Date	2 July	3 July	4 July	5 July	6 July	7 July	8 July	9 July
Time (UTC)	00 06 12 18	00 06 12 18	00 06 12 18	00 06 12 18	00 06 12 18	00 06 12 18	00 06 12 18	00 06 12 18

Early start of monsoon on 19 June 2000: Animations of GOES sounder TPW on 16 and 19 June show influx of moisture into Arizona from the Gulf of California region (produced by Scott Bachmeier of CIMSS). The imagery can be viewed from the "GOES Gallery at CIMSS".

References:

Menzel, W.P., F.C. Holt, T.J. Schmit, R.M. Aune, A.J. Schreiner, G.S. Wade, D.G. Gray, 1998: Application of GOES-8/9 soundings to weather forecasting and nowcasting. Bull. Amer. Meteor. Soc., 79, 2059-2078.

Wu, X., W.P. Menzel, G.S. Wade, 1999: Estimation of sea surface temperatures using GOES-8/9 radiance measurements. Bull. Amer. Meteor. Soc., 80, 1127-1138.