Scientific and Technical Aerospace Reports Volume 39 April 6, 2001

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METEOROLOGY AND CLIMATOLOGY
20010021837 Woods Hole Oceanographic Inst., MA USA
The Northeast Monsoon’s Impact on Mixing, Phytoplankton Biomass and Nutrient Cycling in the Arabian Sea
Wiggert, J. D., Maryland Univ., USA; Jones, B. H., University of Southern California, USA; Dickey, T. D., California Univ., USA;
Brink, K. H., Woods Hole Oceanographic Inst., USA; Weller, R. A., Woods Hole Oceanographic Inst., USA; Marra, J., Lamont-
Doherty Geological Observatory, USA; Codispoti, L. A., Old Dominion Univ., USA; Deep Sea Research; Oct. 22, 2000; ISSN
0967-0645; Volume 47, Part 2, pp. 1353-1385; In English
Contract(s)/Grant(s): NAS5-32484; NAS5-98181; N00014-94-1-0226; N00014-94-1-0362; N00014-96-1-0505;
N00014-94-1-0161; N00014-94-1-0450; NSF OCE-93-10577; NSF OCE-97-12577
Report No.(s): AD-A384575; US-JEGOFS-CONTRIB-486; No Copyright; Avail: CASI; A01, Microfiche; A03, Hardcopy
In the northern Arabian Sea, atmospheric conditions during the Northeast (winter) Monsoon lead to deep convective mixing.
Due to the proximity of the permanent pyncnocline to the sea surface, this mixing does not penetrate below 125 m. However, a
strong nitracline is also present and the deep convection results in significant nitrate flux into the surface waters. This leads to
nitrate concentrations over the upper 100 m that exceed 4 micrometers toward the end of the Monsoon. During the 1994/1995
US JGOFS/Arabian Sea expedition, the mean areal gross primary production over two successive Northeast Monsoons was determined
to be 1.35gC/sq m/d. Thus, despite the deep penetrative convection, high rates of primary productivity were maintained.
An interdisciplinary model was developed to elucidate the biogeochemical processes involved in supporting the elevated productivity.
This model consists of a 1-D mixed-layer model coupled to a set of equations that tracked phytoplankton growth and the
concentration of the two major nutrients (nitrate and ammonium). Zooplankton grazing was parameterized by rate constant determined
by shipboard experiments. Model boundary conditions consist of meteorological time-series measured from the surface
buoy that was part of the ONR Arabian Sea Experiment’s central mooring. Our numerical experiments show that elevated surface
evaporation, and the associated salinization of the mixed layer, strongly contributes to the frequency and penetration depth of the
observed convective mixing. Cooler surface temperatures, increased nitrate entrainment, reduced water column stratification, and
lower near-surface chlorophyll a concentrations all result from this enhanced mixing. The model also captured a dependence on
regenerated nitrogen observed in nutrient uptake experiments performed during the Northeast Monsoon. Our numerical experiments
also indicate that variability in mean pycnocline depth causes up to a 25% reduction in areal chlorophyll a concentration.
We hypothesize that such shifts in pycnocline depth may contribute to the interannual variations in primary production and surface
chlorophyll a concentration that have been previously observed in this region.
Author
Arabian Sea; Phytoplankton; Surface Water; Biogeochemistry; Ammonium Compounds; Convection; Ocean Surface; Monsoons;
Biomass
20010022807 National Center for Atmospheric Research, Boulder, CO USA
Turbulence Algorithm Intercomparison: Winter 2000 Results
Brown, Barbara G., National Center for Atmospheric Research, USA; Mahoney, Jennifer L., National Center for Atmospheric
Research, USA; Bullock, Randy, National Center for Atmospheric Research, USA; Fowler, Tressa L., National Center for Atmospheric
Research, USA; Hart, Joan, Colorado State Univ., USA; Henderson, Judy, National Center for Atmospheric Research,
USA; Loughe, Andrew, Colorado State Univ., USA; December 2000; 68p; In English
Report No.(s): PB2001-102745; NOAA-TM-OAR-FSL-26; Copyright; Avail: National Technical Information Service (NTIS)
This report summarizes basic results of a second intercomparison of the capabilities of a number of clear-air turbulence (CAT)
forecasting algorithms to predict the locations of CAT. The algorithms considered in the study include most of the algorithms that
were included in the first intercomparison, which took place during winter 1998-9, as well as two additional algorithms. The algorithm
forecasts are based on output of the Rapid Update Cycle (RUC-2) numerical weather prediction model during the period
10 January through 31 March 2000. Forecasts issued at 1200, 1500, 1800, and 2100 UTC, with 3, 6, 9, and 12 hour lead times
were included in this study. The evaluation also includes the turbulence AIRMETs, the operational turbulence forecast product
that is issued by the NWS Aviation Weather Center (AWC) and is limited to the continental US and to altitudes above 20,000 feet.
Author
Algorithms; Clear Air Turbulence; Numerical Weather Forecasting; Evaluation