Near-surface winds over the south Pacific Ocean

June 14th, 2021 |

SAR Winds over the South Pacific, latitude/longitudes as indicated, at 0544 UTC on 14 June 2021 (click to enlarge)

Synthetic Aperture Radar (SAR) winds from RCM1 (RADARSAT Constellation Mission 1) over the south Pacific Ocean, from this site, show a gradient in wind speeds between 165 W and 168 W. Are there other ways to view this type of wind change over the open ocean?

GOES-17 Derived Motion wind vectors, below, showing 0500 UTC wind speeds between 950 and 800 mb (a different level than the near-surface winds from the SAR data), from Real Earth, below, do not clearly show the difference in winds over this same domain.

GOES-17 Enhanced window infrared (10.3 µm, Band 13) and 950-800 mb winds, 0500 UTC on 14 June 2021 (click to enlarge).  Note that the latitude lines shown are 19.5, 22 and 24.5 South.  The cold cloud top feature near the edge of this scene is also apparent at the beginning of the animation below.

GOES-17 Shortwave infrared imagery from the same time in that region, below, shows consistent westward motion at low levels (it’s hard to distinguish from this animation if the low-level wind speeds change across the domain; the cloud motions are all similar) with eastward motion aloft (that, is: considerable shear!)

GOES-17 3.9 µm imagery over the South Pacific, latitudes/longitude lines shown, from 0500 to 0600 UTC on 14 June 2021 (Click to enlarge)

SAR winds can give information over the open ocean that is difficult to find in other places.

Offshore islands as barriers to fog

June 7th, 2021 |

GOES-16 True-Color imagery, 1301-2101 UTC on 7 June 2021 (Click to animate)

Moist air that moves from the mainland USA to over the north Atlantic will often induce fog formation over those cold shelf waters.  This is a common occurrence (see this blog post, for a recent example) GOES-16 True-color imagery, above, from 1301-2101 UTC on 7 June 2021, shows the northeastward progress of a fog bank. Note how Block Island, Martha’s Vineyard and Nantucket all served as barriers to the fog.  Such behavior is most likely when a strong inversion is in place.  The closest upper air sounding, Upton NY, over eastern Long Island, below, from this site, did show a very strong surface inversion at 1200 UTC as well as brisk southwesterly winds in the lower levels of the atmosphere. The strong inversion would also allow the bow wake to form upwind of the islands, as observed. (The inversion at Upton persisted through the day! 00Z 8 June sounding is here)

Fog does not penetrate far inland along the coast. Solar heating over land will induce vertical mixing that evaporates any fog over land. A similar event occurred on 8 June.

Upton, NY, rawinsonde, 1200 UTC on 7 June 2021 (click to enlarge)

SAR winds over Lake Superior (part II)

June 3rd, 2021 |

SAR Wind Speeds from RCM3 over Lake Superior at 1152 UTC on 3 June 2021 (Click to enlarge)

This past CIMSS Blog Post showed a region of very strong bowing winds diagnosed by Synthetic Aperture Radar (SAR) data and associated with a convective complex over Lake Superior before sunset on 25 May 2021.   On 3 June 2021, shortly after sunrise (SAR overpasses over the Great Lakes typically occur around 0000 and 1200 UTC), SAR winds from RCM3 (RADARSat Constellation Mission 3) (as shown at this website), showed isolated patches over northern Lake Superior of very strong winds — in excess of 25 m/s! (SAR wind imagery is from this website)

GOES-16 visible imagery (0.64 µm), below, from 1120 – 1200 UTC, visualized using CSPP Geosphere, shows the modest convection associated with these winds.

GOES-16 visible (0.64 µm) imagery, 1120-1200 UTC on 3 June 2021 (Click to enlarge)

Standing waves upstream of Nova Scotia

May 26th, 2021 |

GOES-16 Visible (Band 2, 0.64 µm) imagery, 1441 – 2126 UTC on 26 May 2021 (Click to animate)

GOES-16 visible imagery above (click to animate) shows the development of standing waves upwind of southwestern Nova Scotia. These winds developed in a region of low-level southwesterly (i.e., onshore) flow, as shown in the 1806 UTC image below that includes surface observations.  Higher clouds are moving from a more westerly direction, suggesting veering and warm-air advection.

Note the very warm temperatures over interior Nova Scotia in the image below.  This suggests a strong inversion such as is necessary to trap energy that is then manifest as the standing waves.  Indeed, the Yarmouth, NS sounding at 1200 UTC shows surface temperatures near 12 C with temperatures closer to 20 C between 900 and 950 mb;  that works out to be a potential temperature difference of 16.5 K across the inversion.

GOES-16 Band 2 Visible (0.64 µm) imagery at 1806 UTC along with 1800 UTC METAR observations. (Click to enlarge)

(Thanks to Richard DiMaio, Lewis University, for bringing this event to our attention!)