skip to main content


This content will become publicly available on December 1, 2024

Title: Extreme seasonal water-level changes and hydraulic modeling of deep, high-altitude, glacial-carved, Himalayan lakes
Abstract

Himalayan lakes represent critical water resources, culturally important waterbodies, and potential hazards. Some of these lakes experience dramatic water-level changes, responding to seasonal monsoon rains and post-monsoonal draining. To address the paucity of direct observations of hydrology in retreating mountain glacial systems, we describe a field program in a series of high altitude lakes in Sagarmatha National Park, adjacent to Ngozumba, the largest glacier in Nepal. In situ observations find extreme (>12 m) seasonal water-level changes in a 60-m deep lateral-moraine-dammed lake (lacking surface outflow), during a 16-month period, equivalent to a 5$$\times 10^6$$×106m$$^3$$3volume change annually. The water column thermal structure was also monitored over the same period. A hydraulic model is constructed, validated against observed water levels, and used to estimate hydraulic conductivities of the moraine soils damming the lake and improves our understanding of this complex hydrological system. Our findings indicate that lake level compared to the damming glacier surface height is the key criterion for large lake fluctuations, while lakes lying below the glacier surface, regulated by surface outflow, possess only minor seasonal water-level fluctuations. Thus, lakes adjacent to glaciers may exhibit very different filling/draining dynamics based on presence/absence of surface outflows and elevation relative to retreating glaciers, and consequently may have very different fates in the next few decades as the climate warms.

 
more » « less
Award ID(s):
1910824
NSF-PAR ID:
10501844
Author(s) / Creator(s):
; ; ; ; ;
Publisher / Repository:
Nature Publishing Group
Date Published:
Journal Name:
Scientific Reports
Volume:
13
Issue:
1
ISSN:
2045-2322
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    The electricE1 and magneticM1 dipole responses of the$$N=Z$$N=Znucleus$$^{24}$$24Mg were investigated in an inelastic photon scattering experiment. The 13.0 MeV electrons, which were used to produce the unpolarised bremsstrahlung in the entrance channel of the$$^{24}$$24Mg($$\gamma ,\gamma ^{\prime }$$γ,γ) reaction, were delivered by the ELBE accelerator of the Helmholtz-Zentrum Dresden-Rossendorf. The collimated bremsstrahlung photons excited one$$J^{\pi }=1^-$$Jπ=1-, four$$J^{\pi }=1^+$$Jπ=1+, and six$$J^{\pi }=2^+$$Jπ=2+states in$$^{24}$$24Mg. De-excitation$$\gamma $$γrays were detected using the four high-purity germanium detectors of the$$\gamma $$γELBE setup, which is dedicated to nuclear resonance fluorescence experiments. In the energy region up to 13.0 MeV a total$$B(M1)\uparrow = 2.7(3)~\mu _N^2$$B(M1)=2.7(3)μN2is observed, but this$$N=Z$$N=Znucleus exhibits only marginalE1 strength of less than$$\sum B(E1)\uparrow \le 0.61 \times 10^{-3}$$B(E1)0.61×10-3 e$$^2 \, $$2fm$$^2$$2. The$$B(\varPi 1, 1^{\pi }_i \rightarrow 2^+_1)/B(\varPi 1, 1^{\pi }_i \rightarrow 0^+_{gs})$$B(Π1,1iπ21+)/B(Π1,1iπ0gs+)branching ratios in combination with the expected results from the Alaga rules demonstrate thatKis a good approximative quantum number for$$^{24}$$24Mg. The use of the known$$\rho ^2(E0, 0^+_2 \rightarrow 0^+_{gs})$$ρ2(E0,02+0gs+)strength and the measured$$B(M1, 1^+ \rightarrow 0^+_2)/B(M1, 1^+ \rightarrow 0^+_{gs})$$B(M1,1+02+)/B(M1,1+0gs+)branching ratio of the 10.712 MeV$$1^+$$1+level allows, in a two-state mixing model, an extraction of the difference$$\varDelta \beta _2^2$$Δβ22between the prolate ground-state structure and shape-coexisting superdeformed structure built upon the 6432-keV$$0^+_2$$02+level.

     
    more » « less
  2. Abstract

    We present a proof of concept for a spectrally selective thermal mid-IR source based on nanopatterned graphene (NPG) with a typical mobility of CVD-grown graphene (up to 3000$$\hbox {cm}^2\,\hbox {V}^{-1}\,\hbox {s}^{-1}$$cm2V-1s-1), ensuring scalability to large areas. For that, we solve the electrostatic problem of a conducting hyperboloid with an elliptical wormhole in the presence of anin-planeelectric field. The localized surface plasmons (LSPs) on the NPG sheet, partially hybridized with graphene phonons and surface phonons of the neighboring materials, allow for the control and tuning of the thermal emission spectrum in the wavelength regime from$$\lambda =3$$λ=3to 12$$\upmu$$μm by adjusting the size of and distance between the circular holes in a hexagonal or square lattice structure. Most importantly, the LSPs along with an optical cavity increase the emittance of graphene from about 2.3% for pristine graphene to 80% for NPG, thereby outperforming state-of-the-art pristine graphene light sources operating in the near-infrared by at least a factor of 100. According to our COMSOL calculations, a maximum emission power per area of$$11\times 10^3$$11×103W/$$\hbox {m}^2$$m2at$$T=2000$$T=2000K for a bias voltage of$$V=23$$V=23V is achieved by controlling the temperature of the hot electrons through the Joule heating. By generalizing Planck’s theory to any grey body and deriving the completely general nonlocal fluctuation-dissipation theorem with nonlocal response of surface plasmons in the random phase approximation, we show that the coherence length of the graphene plasmons and the thermally emitted photons can be as large as 13$$\upmu$$μm and 150$$\upmu$$μm, respectively, providing the opportunity to create phased arrays made of nanoantennas represented by the holes in NPG. The spatial phase variation of the coherence allows for beamsteering of the thermal emission in the range between$$12^\circ$$12and$$80^\circ$$80by tuning the Fermi energy between$$E_F=1.0$$EF=1.0eV and$$E_F=0.25$$EF=0.25eV through the gate voltage. Our analysis of the nonlocal hydrodynamic response leads to the conjecture that the diffusion length and viscosity in graphene are frequency-dependent. Using finite-difference time domain calculations, coupled mode theory, and RPA, we develop the model of a mid-IR light source based on NPG, which will pave the way to graphene-based optical mid-IR communication, mid-IR color displays, mid-IR spectroscopy, and virus detection.

     
    more » « less
  3. Abstract

    We introduce a family of Finsler metrics, called the$$L^p$$Lp-Fisher–Rao metrics$$F_p$$Fp, for$$p\in (1,\infty )$$p(1,), which generalizes the classical Fisher–Rao metric$$F_2$$F2, both on the space of densities$${\text {Dens}}_+(M)$$Dens+(M)and probability densities$${\text {Prob}}(M)$$Prob(M). We then study their relations to the Amari–C̆encov$$\alpha $$α-connections$$\nabla ^{(\alpha )}$$(α)from information geometry: on$${\text {Dens}}_+(M)$$Dens+(M), the geodesic equations of$$F_p$$Fpand$$\nabla ^{(\alpha )}$$(α)coincide, for$$p = 2/(1-\alpha )$$p=2/(1-α). Both are pullbacks of canonical constructions on$$L^p(M)$$Lp(M), in which geodesics are simply straight lines. In particular, this gives a new variational interpretation of$$\alpha $$α-geodesics as being energy minimizing curves. On$${\text {Prob}}(M)$$Prob(M), the$$F_p$$Fpand$$\nabla ^{(\alpha )}$$(α)geodesics can still be thought as pullbacks of natural operations on the unit sphere in$$L^p(M)$$Lp(M), but in this case they no longer coincide unless$$p=2$$p=2. Using this transformation, we solve the geodesic equation of the$$\alpha $$α-connection by showing that the geodesic are pullbacks of projections of straight lines onto the unit sphere, and they always cease to exists after finite time when they leave the positive part of the sphere. This unveils the geometric structure of solutions to the generalized Proudman–Johnson equations, and generalizes them to higher dimensions. In addition, we calculate the associate tensors of$$F_p$$Fp, and study their relation to$$\nabla ^{(\alpha )}$$(α).

     
    more » « less
  4. Abstract

    Let$$\phi $$ϕbe a positive map from the$$n\times n$$n×nmatrices$$\mathcal {M}_n$$Mnto the$$m\times m$$m×mmatrices$$\mathcal {M}_m$$Mm. It is known that$$\phi $$ϕis 2-positive if and only if for all$$K\in \mathcal {M}_n$$KMnand all strictly positive$$X\in \mathcal {M}_n$$XMn,$$\phi (K^*X^{-1}K) \geqslant \phi (K)^*\phi (X)^{-1}\phi (K)$$ϕ(KX-1K)ϕ(K)ϕ(X)-1ϕ(K). This inequality is not generally true if$$\phi $$ϕis merely a Schwarz map. We show that the corresponding tracial inequality$${{\,\textrm{Tr}\,}}[\phi (K^*X^{-1}K)] \geqslant {{\,\textrm{Tr}\,}}[\phi (K)^*\phi (X)^{-1}\phi (K)]$$Tr[ϕ(KX-1K)]Tr[ϕ(K)ϕ(X)-1ϕ(K)]holds for a wider class of positive maps that is specified here. We also comment on the connections of this inequality with various monotonicity statements that have found wide use in mathematical physics, and apply it, and a close relative, to obtain some new, definitive results.

     
    more » « less
  5. Abstract

    The pre-ALPACA (Alaskan Layered Pollution And Chemical Analysis) 2019 winter campaign took place in Fairbanks, Alaska, in November–December 2019. One objective of the campaign was to study the life-cycle of surface-based temperature inversions and the associated surface energy budget changes. Several instruments, including a 4-component radiometer and sonic anemometer were deployed in the open, snow-covered University of Alaska Fairbanks (UAF) Campus Agricultural Field. A local flow from a connecting valley occurs at this site. This flow is characterized by locally elevated wind speeds (greater than 3 m s$$^{-1}$$-1) under clear-sky conditions and a north-westerly direction. It is notably different to the wind observed at the airport more than 3.5 km to the south-west. The surface energy budget at the UAF Field site exhibits two preferential modes. In the first mode, turbulent sensible heat and net longwave fluxes are close to 0 W m$$^{-2}$$-2, linked to the presence of clouds and generally low winds. In the second, the net longwave flux is around − 50 W m$$^{-2}$$-2and the turbulent sensible heat flux is around 15 W m$$^{-2}$$-2, linked to clear skies and elevated wind speeds. The development of surface-based temperature inversions at the field is hindered compared to the airport because the local flow sustains vertical mixing. In this second mode the residual of the surface energy budget is large, possibly due to horizontal temperature advection.

     
    more » « less