Many of the classic images associated with this time of year include strong winds. The cozy cottage engulfed in whipping winds. A family gathering made warmer by the whistling conditions outside. The wind is an important character in our holiday season, but not everyone knows its back-story nor its impact on the natural world around us.
The origin of this season’s wind is linked to two weather phenomena: cold fronts and Nor’easters. A cold front is the leading edge of a temperature drop off. Since cold air is denser than warm air, the pressure difference between the high pressure cold air and low pressure warm air causes the shifting winds. Nor’easters are coastal low pressure zones off the Mid-Atlantic and New England coast. They are largest in the late fall and winter because of the increasing difference in oceanic and terrestrial temperatures, and result in strong, northeastern winds.
As the blustering winds travel up and down the Hudson River Estuary, the wind speeds are recorded by the HRECOS meteorological stations. As expected, the HRECOS data show a significant* difference among seasonal wind speeds. The average wind speed increases from summer to fall and from fall to winter. The HRECOS data also show that the HRECOS stations experience significantly** different wind speeds. A comparison of all the readings recorded in 2009 reveals that the average wind speeds increase from north to south. Wind speeds at Schodack Island (131 miles from the NY Harbor) are lower than those at Norrie Point (85 miles from the NY Harbor) which are lower than those at Piermont Pier (25 miles from the NY Harbor). The one exception is the weather station in the Tivoli Bays (98 miles from the NY Harbor) which reports the lowest wind speeds because it is protected by the bay structure.
The winds have a significant impact on Hudson River conditions. The force of the air movement influences water level in the estuary. In extreme cases, this can result in a blow out tide, an unusually low tide, as was described in the HRECOS story: Interpreting ‘A Day in the Life of the Hudson River’ Using Real-Time Data.
On a more local level, the winds significantly*** influence the dissolved oxygen concentrations in the river. It is not a 1:1 relationship; dissolved oxygen concentrations do not increase for every increase in wind speed. However, plotting the distribution of dissolved oxygen concentrations at different wind speeds, reveals an increase in the mean of the distribution, indicating that the higher dissolved oxygen values are more likely when the wind speeds are higher. This is true for every station and every season.
The wind may be an unseen character in this holiday season, but it plays a significant role in manipulating the conditions of the Hudson River. The HRECOS instruments at all stations except for those in Tivoli Bays will continue monitoring the river's conditions throughout the winter months. To observe the impact of this season's wintry gales, select "Current Conditions" in the menu to the left.
* Seasonal wind speeds were compared using analysis of variance
(ANOVA). To satisfy the balanced design requirement, observations were
aligned by sequential order and missing observations were deleted
across all seasons. For all comparisons, p<0.001.
** Wind speeds at different HRECOS stations were compared using analysis of variance (ANOVA). To satisfy the balanced design requirement, observations were aligned by date and missing observations were deleted across all stations. For all comparisons, p<0.001.
*** A Chi Squared Test for Independence was used to assess the impact of wind speed on dissolved oxygen. For all comparisons, p<0.001.