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�SAILing with SPLASH:�Updates to the 2023 Sublimation of Snow Campaign�

Daniel Hogan,

University of Washington Department of Civil & Environmental Engineering

SAIL/SPLASH Bi-Weekly Meeting

August 22, 2022

Photo Credit: Michael Gallagher (2022)

�

Good morning everyone and thank you for the introduction,

My name is Daniel Hogan, I’m a PhD student at the University of Washington working under Professor Jessica Lundquist. Today I will be presenting on our upcoming sublimation of snow campaign in Gothic, Colorado along with some analysis on this past winter’s SAIL and SPLASH data that will inform our upcoming campaign. I’m proud to represent many of those directly associated with this project, including my advisor Jessica Lundquist and Ethan Gutmann from NCAR, and those assisting with this project including Gijs de Boer, Tilden Meyers, Christopher Cox, John Kochendorfer and Michael Gallagher from SPLASH and Daniel Feldman from SAIL. All assisted with data availability and answering questions. The presentation itself and any mistakes within are my own. With that, let me begin.

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Accurate snow models are imperative to estimate seasonal water availability
Gaps persist between snowfall and river output

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Background & Motivation

Courtesy of USGS

Courtesy of NCRS

Colorado Basin	Snowpack % of Normal	River Discharge % of Normal
2020	111%	66%
2021	80%	47%

2020 Colorado River Basin Discharge

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

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The Transition from Snow to Water Vapor

Sublimation is a large source of uncertainty in snow models (Slater et al. 2001, Xia et al. 2017)

Driven by surface fluxes and blowing snow

Estimates vary widely from 1-50% of seasonal snowfall (Mott 2018)

Difficult to measure in complex terrain, need seasonal measurements

Blowing snow

Sublimation

Water Vapor

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

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Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

Sublimation has Mass and Energy Components

Snow Mass Balance

Snow Surface Energy Balance

mass transfer

of water vapor

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Measurements For Quantifying Sublimation

Snow Mass Balance

Snow Surface Energy Balance

Terrestrial Lidar Scans (TLS)

Snow scales to weigh snow

Snow surface temp

Radiometers

Flux towers

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

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2023 Sublimation of Snow Campaign: Location is Vital

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

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SOS Campaign Setup: October 2022 Deployment

10 m

20 m

10 m

Snow scale

10 m

Primary Wind Direction

Tall towers will observe how shear and submesoscale motions inject intermittent turbulence
Multiple towers detect horizontal variability of turbulence and direction of wave propagation.
Terrestrial laser scanners (TLS) to measure blowing snow density and redistribution.
Snow scales to weigh change in snow water equivalent through time.

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

Our setup at the site will include 3 10-meter towers and 1 20-meter tower, situated in a triangular pattern as depicted on this slide. These towers will have sonic anemometers affixed at multiple levels to measure the profile of turbulent fluxes.

The tall towers will observe how shear and sub-mesoscale motions above the stable boundary layer inject intermittent turbulence.

The multiple towers are intended to try to detect the horizontal variability of turbulence and wave propagation.

Terrestrial lidar scanners affixed to each tower will measure snow surface redistribution through time.

Lastly, snow scales at the base of each tower will weigh the changes in snow water equivalent.

However, a perfect location to study sublimation does not mean it is a perfect location to keep sensitive scientific equipment.

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Snow & Mountains Challenge Sublimation Measurements

Strong Stability Over Snow Dampens Turbulence

More Stable

Less stable

Courtesy of Winter ‘21-’22 SAIL MET and surface temperature measurements

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

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Winter 21’ – ’22 Conditions

Example Strong Near-Surface Inversion on 3 January 2022

Median Inversion Depth: 40 meters

Da

Courtesy of SAIL radiosonde measurements

700 hPa

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

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Winter 21’ – ’22 Conditions

Sunny Conditions Persist (Unlike Seattle…)

90.0%

74.7%

89.1%

86.8%

84.0%

64.2%

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

Courtesy of SAIL Total Sky Imager

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Winter 21’ – ’22 Conditions

Energy is Available to Power Sublimation During Daytime

Away from surface

Towards surface

Solar energy available to sublimate snow

Energy away from

surface at night

Energy away from

surface at night

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

Courtesy of SPLASH RADSYS measurements

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Winter 21’ – ’22 Conditions

Occurrences of Near Surface Inversion

Median Inversion Depth: 40 meters

83.6%

16.4%

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

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Winter 21’ – ’22 Conditions

Blowing Snow Conditions

Adapted from Déry and Taylor (1996)

61.4%

74.4%

57.9%

53.9%

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

10-meter wind speed

2 m/s

Saltation begins

5 m/s

Blowing snow begins

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Winter 21’ – ’22 Conditions

Strong Vapor Pressure Deficits Promote Sublimation/Deposition

Sublimation

Deposition

(surface hoar)

Courtesy of SAIL met station and surface temperature measurements

Stable

Unstable

Transfer coefficient varies with stability

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

Evaporation

Wind and the vapor pressure deficit, or VPD can be connected to the mass transfer of water vapor through the relationship on the upper left. In the case of snow, the air near the snow surface is considered saturated. Looking at the VPD against the 2-meter to surface temperature difference over the winter (as shown on the right), we can find periods when VPD values conducive to sublimation or condensation occur. Sublimation occurs with negative VPD values since the vapor pressure gradient is away from the surface and the temperature difference is positive. Condensation in the form of surface hoar occur with positive VPD values and when the temperature difference is large and positive. These conditions most likely during nights when the surface can get very cold due to radiative cooling.

I do want to highlight that this plot does not necessarily stipulate that deposition is necessarily outweighing sublimation, but these conditions are mostly driven by the temperature difference creating a situation where the saturated vapor pressure at the surface is less than the vapor pressure of the air due to the large differences in temperature between the surface and overlying air

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Winter 21’ – ’22 Conditions

Strong Vapor Pressure Deficits Promote Sublimation/Deposition

Sublimation

Deposition

(surface hoar)

Courtesy of SAIL met station and surface temperature measurements

Stable

Unstable

Transfer coefficient varies with stability

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

Evaporation

Wind and the vapor pressure deficit, or VPD can be connected to the mass transfer of water vapor through the relationship on the upper left. In the case of snow, the air near the snow surface is considered saturated. Looking at the VPD against the 2-meter to surface temperature difference over the winter (as shown on the right), we can find periods when VPD values conducive to sublimation or condensation occur. Sublimation occurs with negative VPD values since the vapor pressure gradient is away from the surface and the temperature difference is positive. Condensation in the form of surface hoar occur with positive VPD values and when the temperature difference is large and positive. These conditions most likely during nights when the surface can get very cold due to radiative cooling.

I do want to highlight that this plot does not necessarily stipulate that deposition is necessarily outweighing sublimation on a seasonal basis, but these conditions are mostly driven by the temperature difference creating a situation where the saturated vapor pressure at the surface is less than the vapor pressure of the air due to the large differences in temperature between the surface and overlying air. This can dampen the estimated sublimation rate using this method, which I will show a bit later

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Winter 21’ – ’22 Conditions

Strong Vapor Pressure Deficits Promote Sublimation/Deposition

Sublimation

Deposition

(surface hoar)

Courtesy of SAIL met station and surface temperature measurements

Stable

Unstable

Transfer coefficient varies with stability

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

Evaporation

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SOS Campaign Hypotheses

Valley wind fields

(measured by SAIL)

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

wind

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Turbulence Regimes

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

Threshold wind speed

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Winter 21’ – ’22 Conditions

Turbulence Regimes

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

To see if these same regimes appear at our site, I plotted turbulent intensity and wind speed over a storm event, a quiescent period and a windy, non-snowy period this past winter. All three plots showed the regime pattern, with turbulent intensity rising quickly after reaching a threshold windspeed. The santa slammer snow event at the end of 2021 had characteristics fit the shear-driven and top-down turbulent regimes. However, with a small mean VPD, not much sublimation would be expected. The quiescent period had weak winds and little time in the shear-driven turbulence regime, but there were periods consistent with the top-down regime. Combined with the strong mean VPD, this period could have had stable surface driven sublimation. The final period is one where shear driven turbulence dominated. With a decently strong vapor gradient and consistent winds above the blowing snow threshold, blowing snow sublimation would be expected.

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Sublimation Estimation

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

Method 1: Eddy Covariance

Data from SAIL ECOR and SPLASH ASFS

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Sublimation Estimation

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

Method 2: Bulk Aerodynamic

Data from SAIL surface temperature measurements and met stations

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Sublimation Estimation

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

Method 3: Penman-Monteith

(Mahrt 2005,

Knowles et al. 2012,

Stigter et al. 2018)

Values from SAIL surface radiation measurements and met stations

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Sublimation Estimation

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

Method 1: Eddy Covariance

Method 2: Bulk Aerodynamic

Method 3: Penman-Monteith

(Mahrt 2005,

Knowles et al. 2012,

Stigter et al. 2018)

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Instrument Locations Around the Watershed

Sublimation & Turbulence

Background & Motivation

SOS Approach

Summary

Avery Picnic

Gothic Townsite

Kettle Ponds

Winter ’21-’22 Conditions

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Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

Seasonal Daily Sublimation Rates – Bulk Aerodynamic Method

Takeaways:

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Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

Seasonal Daily Sublimation Rates – Bulk Aerodynamic Method

Takeaways:

Increases in sublimation rate prior to storm periods

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Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

Seasonal Daily Sublimation Rates – Bulk Aerodynamic Method

Takeaways:

Increases in sublimation rate prior to storm periods
Large sublimation rates correspond to non-stormy wind events

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Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

Seasonal Daily Sublimation Rates – Bulk Aerodynamic Method

Takeaways:

Increases in sublimation rate prior to storm periods
Large sublimation rates correspond to non-stormy wind events
Signals are similar but magnitudes differ between locations

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Jan

Feb

Mar

Apr

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

May

SAIL Bulk Method: 13 mm

SPLASH Bulk Method: 20 mm

Missing Data

Estimated Sublimation Total Jan-May 2022

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Jan

Feb

Mar

Apr

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

May

SAIL Bulk Method: 13 mm

SPLASH Bulk Method: 20 mm

SPLASH Avery Picnic EC: 10 mm

SPLASH Kettle Ponds EC: 11.5 mm

Missing Data

Estimated Sublimation Total Jan-May 2022

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Jan

Feb

Mar

Apr

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

May

SAIL Bulk Method: 13 mm

SPLASH Bulk Method: 20 mm

SPLASH Avery Picnic EC: 10 mm

SPLASH Kettle Ponds EC: 11.5 mm

SAIL Gothic EC: 31 mm*

SAIL Kettle Ponds EC: 14 mm*

Missing Data

*Missing early season data

*Large data gaps

Estimated Sublimation Total Jan-May 2022

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Jan

Feb

Mar

Apr

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

May

SAIL Bulk Method: 13 mm

SPLASH Bulk Method: 20 mm

SPLASH Avery Picnic EC: 10 mm

SPLASH Kettle Ponds EC: 11.5 mm

SAIL Gothic EC: 31 mm*

SAIL Kettle Ponds EC: 14 mm*

Penman Monteith: 41 mm**

Missing Data

**Sensitive to net radiation > 0

*Missing early season data

*Large data gaps

Estimated Sublimation Total Jan-May 2022

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Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

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Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

Sublimation

Deposition

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Sublimation Rates in Different Conditions

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

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Sublimation Rates in Different Conditions

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

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Sublimation Rates in Different Conditions

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

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Sublimation Rates in Different Conditions

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

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Sublimation Rates in Different Conditions

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

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Sublimation Rates in Different Conditions

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

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Sublimation Rates in Different Conditions

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

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Sublimation Rates in Different Conditions

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

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Answering this SOS to help fill the gap between snowfall and water availability

Conditions conducive to sublimation persist throughout the winter

Direction and timing of sublimation match well between locations/methods

- But magnitudes vary widely

Sublimation & Turbulence

Background & Motivation

SOS Approach

Winter ’21-’22 Conditions

Summary

Energy available to sublimate

Blowing snow conditions

Strong vapor pressure gradients

Turbulence generated multiple ways

Contact me: dlhogan@uw.edu

Over this presentation, I detailed our setup for the sublimation of snow campaign and explained why the Gothic, CO site is an ideal location for us to study sublimation in different conditions: energy is available, stable and blowing snow conditions occur, strong VPD gradients persist, and turbulence is generated in multiple ways. Sublimation was calculated using a few different methods from the data available and showed general correlation in timing and direction of sublimation events. However, the magnitudes of sublimation Using data we acquire next winter, we seek to better understand the drivers of sublimation, the seasonal snow mass balance and the snow energy budget. Hopefully, we can answer this “SOS” call and begin to fill the gap that exists between mountain snowpack and water availability.

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Questions?

Niwot Ridge Blowing Snow (courtesy of Cassie Lumbrazo)

Surface hoar at Mt. Rainier (taken by me on 3/6)

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Liston, G. E., and M. Sturm, 1998: A snow-transport model for complex terrain. Journal of Glaciology, 44, 498–516, https://doi.org/10.3189/S0022143000002021.

Mott, R., V. Vionnet, and T. Grünewald, 2018: The Seasonal Snow Cover Dynamics: Review on Wind-Driven Coupling Processes. Frontiers in Earth Science, 6.

Pomeroy, J. W., and D. M. Gray, 1990: Saltation of snow. Water Resources Research, 26, 1583–1594,

Slater, A. G., and Coauthors, 2001: The Representation of Snow in Land Surface Schemes: Results from PILPS 2(d). Journal of Hydrometeorology, 2, 7–25, https://doi.org/10.1175/1525-7541(2001)002<0007:TROSIL>2.0.CO;2.

Sun, J., L. Mahrt, R. M. Banta, and Y. L. Pichugina, 2012: Turbulence Regimes and Turbulence Intermittency in the Stable Boundary Layer during CASES-99. Journal of the Atmospheric Sciences, 69, 338–351, https://doi.org/10.1175/JAS-D-11-082.1.

Xia, Y., D. Mocko, M. Huang, B. Li, M. Rodell, K. E. Mitchell, X. Cai, and M. B. Ek, 2017: Comparison and Assessment of Three Advanced Land Surface Models in Simulating Terrestrial Water Storage Components over the United States. Journal of Hydrometeorology, 18, 625–649, https://doi.org/10.1175/JHM-D-16-0112.1.

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References