An official website of the United States government
We use reanalysis data and satellite remote sensing of cloud properties to examine how meteorological conditions alter the surface energy balance to cause surface melt that is detectable in satellite passive microwave imagery over West Antarctica. This analysis can detect each of the three primary mechanisms for inducing surface melt at a specific location: thermal blanketing involving sensible heat flux and/or longwave heating by optically thick cloud cover, all-wave radiative enhancement by optically thin cloud cover, and föhn winds. We examine case studies over Pine Island and Thwaites Glaciers, which are of interest for ice shelf and ice sheet stability, and over Siple Dome, which is more readily accessible for field work. During January 2015 over Siple Dome we identified a melt event whose origin is an all-wave radiative enhancement by optically thin clouds. During December 2011 over Pine Island and Thwaites Glaciers, we identified a melt event caused mainly by thermal blanketing from optically thick clouds. Over Siple Dome, those same 2011 synoptic conditions yielded a thermal blanketing-driven melt event that was initiated by an impulse of sensible heat flux then prolonged by cloud longwave heating. In contrast, a late-summer thermal blanketing period over Pine Island and Thwaites Glaciers during February 2013 showed surface melt initiated by cloud longwave heating then prolonged by enhanced sensible heat flux. At a location on the Ross Ice Shelf adjacent to the Transantarctic mountains we identified a December 2011 föhn wind case with additional support from automatic weather station data. One limitation thus far with this type of analysis involves uncertainties in the cloud optical properties. Nevertheless, with improvements this type of analysis can enable quantitative prediction of atmospheric stress on the vulnerable Antarctic ice shelves in a steadily warming climate.
more »
« less
Greenland Surface Melt Dominated by Solar and Sensible Heating
Abstract The Greenland Ice Sheet is the primary source of global Barystatic sea‐level rise, and at least half of its recent mass‐loss acceleration is caused by surface meltwater runoff. Previous studies on surface melt have examined various thermodynamic and dynamic drivers, yet their contributions are not compared using unified observations. We use decade‐long in‐situ measurements from automatic weather stations throughout the ablation zone to assess energy components and identify the leading physical processes in this area. Large melt events exceeding 3σcontribute only ∼2% to total surface melt since 2007. The day‐to‐day variability of all melt is dominated by sensible heat exchange (31 ± 7%) and shortwave radiation (28 ± 5%). Sensible and solar heating correlate with the occurrence of dry and fast gravity‐driven winds. These katabatic winds increase sensible heating of the surface mainly by enhancing vertical mixing that reduces the temperature inversion. The concomitant low humidity and clear skies yield increased solar heating.
more »
« less
- Award ID(s):
- 1633631
- PAR ID:
- 10374744
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 48
- Issue:
- 7
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract This study examines the annual cycle of the Surface Energy Budget (SEB) in the Beaufort‐Chukchi seas, focusing on the autumn transition. Shipboard measurements from NASA's Salinity and Stratification at the Sea Ice Edge (SASSIE) experiment (8 September–2 October 2022) and satellite flux analysis for the entire 2022 were utilized to provide a comprehensive perspective of the SEB's seasonal dynamics. An important finding is the alignment of SEB’s autumnal transition with the September 22 equinox, marking the onset of prolonged Arctic darkness. This transition involved a shift from the summertime radiative heating to cooling conditions, characterized by outgoing longwave radiation surpassing incoming solar radiation and a notable increase in synoptic turbulent latent and sensible heat flux variability. The increased turbulent heat fluxes after the equinox were associated with increased occurrences of short‐duration cold air outbreaks. These outbreaks seem to originate from cold mesoscale surface winds transitioning from cooling landmasses or ice caps to the warmer seas, driven by differential cooling rates between land/ice and ocean as solar irradiance declined. Turbulent heat losses, outpacing longwave emission by more than fivefold, accelerated ocean surface cooling in the subsequent 2 months, leading to the complete freeze‐up of the Beaufort‐Chukchi seas by late November. These findings underscore the substantial influence of astronomical seasons on the SEB, emphasizing their crucial role in Arctic climate dynamics.more » « less
-
Abstract A quasi‐27‐day wave (Q27DW) caused by the rotational period of solar radiation is commonly observed in the atmospheric dynamics. In the present study, we report an enhancement of a Q27DW during recurrent geomagnetic storms in the autumn of 2018 based on the zonal wind observations in the mesosphere and lower thermosphere (MLT) region over Beijing (BJ, 40.3°N, 116.2°E). According to our analysis, the solar radiation and the seasonal variation are not important in exciting the observed Q27DW. A 27‐day oscillation exists in both solar wind data andKpindex during the recurrent geomagnetic storms. The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature and ozone data also reveal a Q27DW signature at 97 km. Using the long‐term observation of BJ meteor radar, two more cases are found during springtime in 2010 and 2018 under the solar quiet condition. Our results indicate that the recurrent geomagnetic storms due to high‐speed solar winds can modulate the temperature and ozone in the MLT region, which is responsible for generating a Q27DW in the MLT zonal winds over BJ. This study suggests that the variation of planetary waves in the MLT neutral winds at mid‐latitude is likely associated with the recurrent geomagnetic storms and high‐speed solar winds.more » « less
-
Abstract In conditions of low winds and high insolation, near-surface stratification develops in the ocean that is typically referred to as a diurnal warm layer (DWL). These layers can have a substantial effect on sea surface temperature and air–sea fluxes yet are rarely accounted for in modern global models due to their small vertical scale. Here, we present collocated measurements of vertical temperature and turbulence structures in large DWLs made from a Lagrangian float featuring a robotic lead screw temperature/salinity (T/S) profiler and pulse-to-pulse coherent ADCP as well as a comprehensive suite of meteorological observations above the ocean surface, yielding novel observations of the response of large DWLs to variability in wind and solar forcing at subhourly time scales. Comparison between the observations and a hierarchy of upper-ocean models reveals the importance of an accurate solar heating parameterization and suggests a modification to the critical bulk Richardson number used by default in theK-profile parameterization. Comparison to a simple scaling for DWL evolution highlights its potential as a means of incorporating DWL effects into global-scale modeling, and a new extension to the scaling is developed to remedy its inaccuracy in cases of wind decrease. None of the models tested are able to reproduce the observed response to sudden insolation loss on one of the stations. Significance StatementThis study presents measurements of warm layers of water that can develop on the ocean surface on a calm, sunny day. These layers are widespread in the ocean and change the relationship between the ocean and the atmosphere, but they are hard to include in large models because they are so shallow. By comparing first-of-their-kind observations of these warm layers made by our drifting buoy with several types of physical models, we improve our understanding of them and chart a realistic path toward their inclusion in global models.more » « less
-
Abstract We present measurements of the equatorial topside ionosphere above Jicamarca made during extremely low solar flux conditions during the deep solar minimum of 2019–2020. Measurements were made in October, 2019, February, 2020, and September, 2020. The main features observed are a large and extended decrease in noontime temperatures unlike that seen in studies at moderate solar flux levels, predawn ionospheric heating as early as 0300 LT, large day‐to‐day variability in the O+/H+transition height, and negligible helium ion concentration at all altitudes. Data from the Ion Velocity Meter (IVM) instrument onboard the Ionospheric Connection Explorer (ICON) and the Topside Ionospheric Plasma Monitor (SSIES) onboard the Defense Meteorological Satellite Program (DMSP) satellites are used to assess agreement with ISR data and assist with the analysis of the predawn heating phenomena. We also analyze the data in light of the SAMI2‐PE model which shows less agreement with the data than at higher solar flux. The main areas of discrepancy with the data are outlined, such as the absence of significant predawn heating, less pronounced decreases in noontime temperatures, and much higher O+fractions at high altitudes, particularly in September. Finally, a sensitivity analysis of the model to various forcing agents such as neutral winds, plasma drifts, solar flux, and heat flow is performed. A discussion is presented on bridging the discrepancies in future model runs. Novel techniques of clutter removal and noise power bias correction are introduced and described in the appendices.more » « less
