METEOR-20240911#
Summary#
RV Meteor began its activities early this morning, collecting our wayward drift buoy from 8.13N, 35.83W at 6 AM LT in the pouring rain, 20-30 kt southwesterly winds, and moderate seas. We were just south of a confluence zone and southwest-northeast elongated trough axis associated with then Invest 93L, which was classified as Tropical Depression 7 in the afternoon (thus indicating TC formation). We then headed back west towards our next target, one of the gliders, fighting against the winds and current and getting battered by 2 m waves across our beam. The seas were an unwelcome reprise of our early days after departing Mindelo. By midday the wind had slackened a bit and the seas were calmer, allowing us to deploy the rubber boat to successfuly retrieve the first of our three gliders at 8.21N, 36.5W. Following this, it was a race to the WNW to try to find the next glider and WireWalker before we lost daylight. We were able to retrieve the next glider from 8.50N, 37.18W around dinnertime, and the WireWalker from 8.52N, 37.28W about an hour later!
We also had our usual daily briefing and science discussion at 10:20 LT, in which Michael Bell presented about polarimetric radar applications. In our AP period (after polarimetric, or “post-Praia”) after SEA-POL was repaired, we are transmitting and receiving horizontally and vertically oriented waves simultaneously. Differences between the horizontal and vertical waves are related to the shape, orientation, and number of hydrometeor targets. Thus, the additional polarimetric variables beyond reflectivity can help us retrieve more information about the microphysical structure of the hydrometeors and their type, as well as constrain the reflectivity-rainfall relationship.
Zdr, or differential reflectivity, is the difference between the horizontal and vertical reflectivities. It is zero for spherical droplets, positive for horizontally-oriented droplets (raindrops, which flatten as they fall), and negative for vertically-oriented droplets like ice crystals. Larger values of Zdr indicate large drops. \(\rho_{hv}\) is the correlation coefficient between the horizontal and vertical pulses. The linear Zdr ratio is 1 for spherical targets and less than 1 for a non-uniform mixture of rain and snow. We also use it as a quality control metric to remove non-meteorological echos, which have a correlation coefficient of much less than 1. Thus, the quality of even our regular reflectivity retrievals is improved with polarimetric data. Kdp, or specific differential phase, depends strongly on the number concentration and is a good meaure of rain rate above a certain threshold. Finally, Ldr, or linear depolarization ratio can also be measured by dual-polarimetric radars, but this is most relevant for vertically pointing radars, like the W-band cloud radar on board. SEA-POL can’t measure Ldr in its current configuration because we are sending and receiving the horizontal and vertical pulses simultaneously.
For the SEA-POL retrievals on board Meteor, we will use the polarimetric data to perform high-quality rainfall retrievals and hydrometeor identification. We will also use disdrometer and polarimetric retrievals from the AP period to constrain the reflectivity-rainfall relationship from the BP (before polarimetric/Praia) period. Michael also discussed some of his science objectives, which recognize that the size, number and habit of hydrometeors is determined by the energetics of cloud systems and their surrounding environment. He is working on a new metric of precipitation kinetic energy called the “temprian” that can be estimated from polarimetric moments measured by SEA-POL. Combining the temprian with reflectivity will allow us to recover the drop size distribution.
Remarks#
Meteor is in the UTC-2 time zone.
Radiosondes were launched on the normal 3-hourly schedule.
STRINQS has ceased operations.
Plans#
12.09 - 16.09: Recover the last glider near the Pirata buoy at 8N, 38W, then head west towards 10N, 47W
Events#
Time (Local) |
Comment |
|---|---|
08:13 - 06:23 |
Retrieved drift buoy |
10:20 |
Meeting led by D. Klocke, science presentation by M. Bell |
11:45 - 11:55 |
Retrieved glider |
17:15 - 17:24 |
Retrieved glider |
18:18 - 19:02 |
Retrieved drift buoy with WireWalker |