Mission Plan :

NOAA42 will conduct a research mission in the East Pacific for the HFP-IFEX Genesis Stage Experiment, Objectives #1 (Precipitation Mode) and #2 (Pouch). The initial plan calls for a square spiral pattern (Fig. 1), with a width of 3x3 degrees on the outer square and 1x1 degree in the inner square. Dropsondes will be released at each of the corners of the two squares, as well as 2 equally spaced sondes (every 1 degree) on the northern, western, and southern edges of the outer square. The pattern will be flown at 12 kft pressure to accommodate the IWRAP data collection. We will attempt to do include TDR analyses on the way in and out, fairly close to the starting and ending points of the square-spiral pattern. The square spiral will be flown counterclockwise.

Figure 2. IR satellite image of Invest EP96 at 0900 UTC 28 September

Figure 3. IR satellite image of Invest EP96 overlaid with the 0845 UTC 28 September 850-200 hPa, deep-layer CIMSS shear magnitude

EP96 is certainly looking healthier this morning, especially considering a large convective burst has developed just southeast of the apparent broad surface / low-level circulation center (Fig. 2) (between 9-12°N / 94-96°W) While that surface circulation is likely still quite broad, increasing convective/stratiform activity close to that region could allow it to consolidate some today. The mesoscale convective system (MCS) currently located to the south and east certainly could be influential in terms of developing a mid-tropospheric convective vortex (MCV), which could subsequently be a focal point for surface spin up. NHC has given EP96 a 70/90% chance of formation in 2/5 days, which is consistent of having increased convective coverage, a clear circulation at low-levels, and optimistic global model forecasts. The only hindrance at the moment seems to be a high shear zone bordering the disturbance on the north side (Fig. 3). This has caused a significant shear gradient over the area of the disturbance. This would certainly suggest that the 3 kt analyzed for the SHIPS deep layer shear is likely not indicative of the actual environmental shear magnitude, and what the disturbance is actually experiencing. This could result in a separation of any midlevel circulation from the low-level, and perhaps result in the intrusion or production of dry air from subsidence over the low or surface circulation, causing stabilization and inhibited convective development in the area that needs it the most for genesis.

We have moved the initially planned square spiral pattern 1 degree west to accommodate the slower speed of the disturbance than the models suggested yesterday, centering it at 11°N/98°W. This will hopefully capture the surface circulation we observed yesterday again, as well as any MCVs within the precipitation region.

Figure 4. Actual flight track for mission 20180928H1. Flight-level winds (barbs) and wind speeds (shaded, kt) indicated.

Mission Summary :

The actual track of the mission is shown in Fig. 4, with wind information at flight level (FL), extrapolated sea level pressure (SLP), and SFMR surface wind speed and rain rate shown in Fig. 5. The transit to the IP of the outer square (northeast corner) was about 2 hr. On our way in, we passed just north of the MCS we observed on satellite that developed east of the apparent broad circulation overnight (Figs. 2, 6). We reached the IP near 12.5°N / 96.5°W at 1504 UTC (Sonde #1) and began our westbound trek on the northern side of the outer square. We dropped both intermediate sondes along the leg at 12.5°N at 1516 (WP #2) and 1529 (WP #3) UTC (Sondes #2, #3). There was some scattered deep convection (Fig. 6) to our north on the leg, which was allowing us to get TDR returns, helping to produce a better analysis (Fig. 7, Fig. 8). Sondes showed 30 kt easterly winds higher up towards flight level, with a bit of weaker easterly winds towards the surface (Fig. 9). We arrived at WP #4 near 12.5°N/99.5°W, the northwest end point of the westbound leg at 1543 UTC (Sonde #4; IR Sonde #1). This was an IR sonde drop and the release was delayed a few minutes until we were able to see the ocean below. Once dropped we had passed the original turnpoint, so we had to maneuver back to the original north to south line.

Figure 5. Time series of flight-level wind speed (green, kt), SFMR surface wind speed (blue, kt), and SFMR rain rate (red, mm/hr) for mission 20180928H1, as well as the extrapolated surface pressure (mb) (bottom, teal, mb) and altitude of the aircraft (bottom, black, m).

Figure 6. IR satellite image of Invest EP96 at 1500 UTC 28 September

On the southbound line along 99.5°W (between 12.5° and 9.5°N) on the west side of the outer square, we dropped intermediate sondes at 1558 (WP #5) and 1611 (WP #6) UTC. Along this line we observed shallow to moderately deep congestus with some isolated deeper congestus (Fig. 6). Surprisingly the sondes at WP #5 and WP #6 observed easterlies at the surface (Fig. 9) (expected to see some westerly or northerly component if the square was centered on the surface circulation), witch would not be consistent with having the low-level circulation there. The sonde at the southwest point of the outer square (WP #7, Sonde #7) did, however, have a weak (5 kt) westerly wind at the surface (Fig. 9). This suggests that we did pass through a possible surface circulation, thought it was difficult to know whether it was associated with the coherent, broad circulation we were expecting to see. We reached WP #7 at 1624 UTC (IR Sonde #2) near 9.5°N/99.5°W. Sky conditions were mostly clear in this region, with little in the way of congestus buildup. We also observed a wind shift at flight level in this southwest side (Fig. 4), indicative of possibly an elongated trough or circulation, or an MCV (though MCV not likely considering the region has been mostly absent of precipitation).

Figure 7: Composite reflectivity and winds at (left) 2 km, as well as (right) windspeed at 2 km (shaded) and streamlines at 2 (black) and 5 km (grey)

The next leg was west to east along 9.5°N (between 99.5° and 96.5°W), bordering the southern side of the outer square. We dropped both intermediate sondes at 1638 (WP #8) and 1651 (WP #9) UTC (Sondes #8 and #9). Up to 15 kt southerly winds were observed in these sondes at the surface (Fig. 9) up to flight level (Figs. 7, 8), consistent with the cloud motion in low-levels observed in the visible satellite. As we reached WP #10 near 9.5°N/96.5°W around 1706 UTC on the southeast side of the outer square, we were approaching the large MCS. We were able to drop our third IR sonde (Sonde #10; IR Sonde #3) in decent conditions below the aircraft (just scattered clouds), and turned northbound for our last south to north leg (between 9.5° and 11.5°N) to complete the outer square. The IR sonde at WP #10 appeared to have a questionable fall rate, so we dropped a backup sonde (regular RD94) at 1711 UTC (Sonde #11). Once we got more north, we entered a stratiform rain region (Fig. 7). Given that a new convective line had developed near the northeast point of our inner square (near 11.5°N / 97.5°) (Fig. 10), we opted to extend the northbound leg some in order to deviate safely around that line to its north. We dropped both sondes on the northbound leg at 1719 UTC (WP#11, Sonde #12) and 1733 UTC (WP #12, Sonde #13). As expected, these sondes had mostly southerly winds over their depth to the surface (Fig. 9). On this track we also observed another wind shift at flight level; from westerly to easterly (Figs. 4, and 7, 8 right panels). This would certainly suggest a midlevel circulation (MCV) within the stratiform rain region we were flying through. The TDR analysis, in fact, shows a very distinct, coherent MCV in the stratiform rain region to the east of the aircraft position (Fig. 7)

Figure 8: Composite winds at (left) 0.5 and (right) 4 km

We flew through the new convection forming near the northeast point of our inner square near 11.5°/97.5°W (and on the western edge of the older MCS), dropping a sonde at WP #13 at 1749 UTC (Sonde #13). We had decent turbulence in the convective line, most notably one we got through the leading edge (Fig. 10). We reached the northwest corner of the inner square (WP# 14) near 11.5°N/98.5°W at 1803 UTC (Sonde #14; IR Sonde #4) and dropped an IR sonde, given that it was clear below the aircraft. This sonde reported 1006.3 mb surface pressure, the lowest observed so far (Fig. 9). We turned south and reached the southwest corner of the inner square (WP #15) at 1816 UTC (Sonde #16) near 10.5°N/98.5°W, where we saw the clearest conditions of the whole pattern (Fig. 10). The southerly surface winds for the two western sondes of the inner square (Fig. 9) would suggest that any existing surface circulation would have moved west of our inner square at the time we flew it. We then turned east and arrived at the southeast corner (WP# 16) at 1829 UTC (Sonde #17) near 10.5°N/97.5°W. We finally turned northward and returned to the northeastern-most point of the inner square (WP #17) at 1843 UTC near 11.5°N/97.5°W. We decided to drop another sonde at this location to get some time evolution from the one we dropped about an hour earlier at 1748 UTC.

Figure 9: Surface winds from each dropsonde during 20180928H1

Figure 10. Visible satellite image of Invest EP96 at 1800 UTC 28 September

We exited the storm to the east, passing through the large stratiform rain region associated with the convective system we observed throughout the time on station (and that developed much before our arrival). The TDR analyses showed a coherent midlevel circulation in this region earlier on our south to north pass of the outer square (Figs. 7, 8), and this pass would allow us to get some time evolution of that feature. The TDR analysis on the outbound leg, did in fact shown the MCV again. Overall this MCS was very persistent, even developing new convection on its western edge, that we passed through on the eastern edge of inner square. As we left, convection continued to grow on the eastern, northern, and western sides of the disturbance, with the southern side having the least convective development. There were decent southerly and easterly winds, and if the circulation can become more coherent (and maybe aligned?) in the low and mid-levels, the storm could soon develop. It does, however, appear to have to overcome some dry air within the broad surface trough or circulation, which could be impacted by the apparent westerly shear.

Mission Evaluation / Problems :

Overall, this was a very interesting mission during the potential genesis of EP96. Through the square spiral pattern we were able to observe what appeared to be a surface circulation or trough axis west of the main convective area, on the eastern side of the surface circulation or trough and edge of our pattern. The surface wind shift occurred in the west and southwest portion of the outer square (Fig. 9). When we returned to that region to fly the inner square, winds were predominantly southerly, suggesting that the surface circulation or trough had moved off to the west of our position (Fig. 9). We also observed a couple of distinct wind shifts at flight level. One was located in that same southwest portion of the outer square, while the other was observed on the eastern edge of the pattern in the stratiform precipitation region (Fig. 4). The TDR analyses (Figs. 7, 8), as well as flight level winds (Fig. 4), indicated a coherent MCV in that MCS. The MCS remained rather persistent during our time on station, with some new development on the west side of the MCS, along the eastern portion of our pattern. On the transit home we went through quite a bit of stratiform precipitation, and kept the TDR running to perhaps observe some time evolution of the MCV. It seems likely that the MCV was very coherent, and long lasting, considering it very clearly shows up in the composite TDR analyses (Figs. 7, 8). The question is: could this be a focal point for surface spinup within the apparently broad surface circulation or trough?

Overall, it does appear that some westerly vertical wind shear could be impacting the disturbance, keeping the greatest deep convection coverage predominantly to the east of any surface circulation/trough. Throughout all levels, though, there were likely multiple centers (particularly within the midtroposphere), which makes this mission more difficult to analyze. We did observe quite a bit of moderately deep and deep congestus development on the north and west sides of the pattern, too, indicating that generally the environment is fairly unstable in the low to middle troposphere, and favorable for further convective development. That said, we observed some fairly thermodynamically stable air within the square (perhaps near the center of the surface circulation/trough axis) that was void of any convection of depth. Perhaps some subsidence aloft, not observed by these shallower sondes, would suggest that dry air and stability could be preventing additional convective growth and coverage in that region.

The lowest MSLP we observed from a dropsonde was 1006.3 mb, with 40 kt easterly winds on our inbound to the northeast point, and 20-30 kt southerlies feeding into the MCS on the south and into the eastern portion of the pattern. NHC has increased the probability of formation in 48 hours to 80%, and keeping the probability 90% in 5 days. It may need to move away from that high shear region and gradient, apparently present during today’s mission (Fig. 3) to get promote further development. If it does, we may see more coverage of convection tomorrow and, possibly, the official genesis (at least TD) of EP96.

The only issue on the flight was that the wing pod, operational SFMR was not working (issue that cropped in the first mission of the sequence). The LIPF (2nd, research) SFMR in the belly was being used in its place. Otherwise the pattern was flown with very little deviations. Generally when deviations did occur they were done early to keep with smooth turns to help maintain the quality of the TDR analyses.

Jon Zawislak
Oct. 4, 2018

Flight track

Temperature and Moisture

Wind and Atlitude

Flight track

Altitude, Pressure, Rain Rate, and Wind

Flight Director's log | Flight Director's manifest | NetCDF data | serial data 1 second data
LPS log | Radar log | Drop log

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