April 1, 2004, was a sunny spring day for most of Scandinavia and the Baltic States, though a region of hazy air lurked offshore to the west and to the south. The cloud-free skies gave the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) on the OrbView-2 satellite a clear view of the Baltic region. On the left, the lingering snow highlights the varied geology of the Scandinavian Peninsula. The thick snow that clings to Norway’s mountains provides a stark contrast to the dark fingers of water, fjords, that cut into the land, making it appear even more formidable. To the east, the snow has largely melted, remaining only in Sweden’s northern highlands. The forests of the south are bringing hints of green to the winter-brown land.

Green and brown clouds of sediment taint the waters of the Gulf of Riga and the Gulf of Gdansk, as much a sign of spring as the disappearing snow and greening landscape. As the temperatures climb, melting snow swells the rivers that snake through the Baltic lowlands, sweeping dirt into the Baltic Sea. The sediment colors the water brown where the dirt is concentrated, and green, when it is dispersed. Here, the Daugava River is sending a muddy plume into the Gulf of Riga in Latvia, while to its south, Poland’s Wisla River is only clouding the Gulf of Gdansk enough to color the water green.

SeaWiFS views Spring Runoff in the Baltic Sea

Gene Feldman, NASA GSFC, Laboratory for Hydrospheric Processes, Office for Global Carbon Studies (gene.c.feldman@nasa.gov)

SeaWiFS views Spring Runoff in the Baltic Sea

Decline of Subpolar North Atlantic Circulation During the 1990s

Sirpa Häkkinen, NASA GSFC, Laboratory for Hydrospheric Processes, Oceans and Ice Branch (sirpa.hakkinen@nasa.gov) and Peter B. Rhines

Observations of sea surface height reveal that dramatic changes have occurred over the past decade in the mid-to-high-latitude North Atlantic Ocean. TOPEX/ Poseidon altimeter data show that subpolar sea surface height increased during the 1990s and the geostrophic velocity derived from altimeter data exhibits declining subpolar gyre circulation. Combining the data from earlier satellites, we find that subpolar circulation may have been weaker in the late 1990s than in the late 1970s and 1980s. Direct current-meter observations in the boundary current of the Labrador Sea support the weakening circulation trend of the 1990s and, together with hydrographic data show that the mid-to-late 1990s decline extends deep in the water column. Analysis of the local surface forcing suggests that the 1990s buoyancy forcing has a dynamic effect consistent with altimetric and hydrographic observations: a weak thermohaline forcing allows the decay of the domed structure of subpolar isopycnals and weakening of circulation.

Trend in the geostrophic velocity from 1992-2002 derived from TOPEX/Poseidon-ERS1/2 data

LEFT: The trend of the geostrophic velocities (m/s per decade) derived from altimeter data for the period 1992 May to 2002 June. Vector colors represent the t-test value. Values above 2.0 are significant at 95% level, only vectors above this significance level are shown. Velocities above 0.05m/s per decade are truncated.

EOF1 of the geostrophic velocity(BELOW LEFT) field derived from the altimeter data with 9.4% of the variance. The vectors are non-dimensional due to normalization of each velocity component by the standard deviation of the current speed anomaly. PC1 of the geostophic Velocity (BELOW) field in non-dimensional units.

SATELLITE-BASED ESTIMATION OF AERODYNAMIC ROUGHNESS FOR GLOBAL CLIMATE STUDIES

 

Michael F. Jasinski (Michael.F.Jasinski@nasa.gov)NASA Goddard Space Flight Center, Hydrological Science Branch, Greenbelt, MD

Jordan Borak Science Systems and Applications, Inc.

Richard Crago Bucknell University, Lewisburg, PA

Background and relevance to NASAAlmost all atmospheric simulation and land data assimilation models used by NASA or other weather and climate agencies today assign aerodynamic roughness lengths using a rather crude look-up table procedure based on land class. However, recent advances in combining a boundary layer with bulk vegetation attributes, have established the feasibility for estimating roughness from space-based estimates of vegetation data products such as those provided through MODIS. When employed in the above models, the results should lead to improved prediction of global momentum and scalar fluxes.

ObjectiveThere are two principal objectives: i.) To test and further refine a theoretical approach for estimating momentum aerodynamic roughness and displacement height using satellite multi-spectral imagery, and ii.) To adapt the method to the NASA MODIS data.

ApproachResearch is based on a theoretical development in canopy turbulence by Raupach (1992, 1994). His formulation for roughness depends on the canopy frontal area index, which is closely related to the canopy shape and architecture. Jasinski and Crago (1999) developed a technique to estimate the canopy area index of a pixel from geometric modeling of individual canopy elements, assuming elements in pixels follow a Poisson distribution. The technique can be used to estimate canopy area index, and thus roughness and displacement heightfrom satellite imagery.

ResultsFigure 1 shows the theoretical canopy area index parameterized in terms of fractional vegetation cover and one non-dimensional geometric similarity parameter (Jasinski and Crago, AFM 94,1999, 65-77). Figure 2 demonstrates its application to the Landes Forest of the 1986 HAPEX Mobilhy Experiment in Lubbon, France. Figure 3 presents results for a 105 sq. km. region within the Southern Study Area of the 1994 BOREAS Experiment in Canada. Comparisons of model results with field data support the validity of the methodology. When applied to improved satellite imagery from MODIS at continental scales the method should provide a unique dataset of roughness length that can be incorporated into the next generation of numerical climate and hydrology models.

10-3

10-2

10-1

100

0.0 0.2 0.4 0.6 0.8 1.0

zo/h

m

Gash et al. (1989)

Parlange and Brutsaert(1989)

Theoretical parameterizationJasinski and Crago (1999)

N = 6.1assumes h = 10massumes h = 20m

Fig. 2. Theoretical and observed momentum roughness for HAPEX-Mobilhy, 1986 (Jasinski and Crago, 1999).

Fig. 1. Parameterization of Canopy Area Index in terms of fractional vegetation cover (Jasinski and Crago, 1999).

10-2

10-1

100

101

102

0.0 0.2 0.4 0.6 0.8 1.0

Fractional cover or "m"

N = canopy surface area/projected area

Momentum Aerodynamic Roughness Length of BOREAS SSA

0.01 0.02 0.03 0.04 0.05 0.06

53.580 N 104.251 W

54.525 N 105.757 W Fig 3. Map of momentum aerodynamic

roughness length normalized by canopy height, for a 105x105 sq. km portion of the BOREAS Southern Study Area.

SATELLITE-BASED ESTIMATION OF AERODYNAMIC ROUGHNESS FOR GLOBAL CLIMATE STUDIES

Ground penetrating radar simulations for Jupiter’s Icy moons

Thorsten Markus, NASA GSFC, Lab. for Hydrospheric Processes, Microwave Sensors Branch (thorsten.markus@nasa.gov)with J.L. Green, J.F. Cooper, S.F. Fung, W.W.L. Taylor, R.F. Benson, Code 600

S.P. Gogineni, U. Kansas, Lawrence, KSB.W. Reinisch, P. Song, U. Massachusetts, Lowell, MA

•The detection of subsurface oceans underneath the icy crust of the Jovian moons is one of the primary objectives of the Jupiter Icy Moons Orbiter (JIMO) mission.

•We proposed (and most recently were informed to get funded) a radio sounder that operates in the frequency range from 1 kHz to 50 MHz. With this instrument a number of scientific measurements can be made (Figure 1). At frequencies less than about 1 MHz is radar signal is reflected by the ionosphere and the magnetosphere enabling ionospheric and magnetospheric measurements. At frequencies above 1 MHz the signal, which passes through the ionosphere to the surface, will be used to explore subsurface properties.

•Besides the direct detection of an ocean, questions are whether the ice is convecting or not. This determinesthe temperature profile within the ice layer.

•Initial modeling results, simulating a surface-penetrating radar system, show that an ocean underneath the ice (Cases B and C) is clearly distinguishable from the case with bedrock at the bottom (Cases A and D) (Figure 2).

•Further simlulations will be carried out in order to determine optimum radar parameters. This includes simulations with a wide variety of subsurface scenarios and surface roughnesses, as well as different radar waveforms.

•Reference: Markus, T., et al., Ground penetrating radar simulations for Jupiter’s icy moons, Tenth International Conference on Ground Penetrating Radar, 21-24 June, 2004, Delft, The Netherlands, 2004.

(1) Possible scientific measurements of Jupiter’s icy moons using a radar sounder with a frequency range from 1 kHz to 50 MHz.

(2) Radar simluations for typical Europa scenarioswith ocean (B,C) and bedrock (A,D) underneatha 7-km layer of ice.

Ground penetrating radar simulations for Jupiter’s Icy moons

Thorsten Markus, NASA GSFC, Lab. for Hydrospheric Processes, Microwave Sensors Branch (thorsten.markus@nasa.gov) with J.L. Green, J.F. Cooper, S.F. Fung, W.W.L. Taylor, R.F. Benson, Code 600

S.P. Gogineni, U. Kansas, Lawrence, KSB.W. Reinisch, P. Song, U. Massachusetts, Lowell, MA