Nudging Time-Scale Sensitivity of a Simplified Black Sea CIL Forcing with a Three-Dimensional Idealized Bosphorus Hydrodynamic Model

Year 2019, Volume: 4 Issue: 2, 230 - 242, 31.08.2019

Adil Sözer , Emin Özsoy

https://doi.org/10.35229/jaes.572713

Abstract

Hydrodynamics of the Bosphorus Strait is examined under idealized
conditions with a three-dimensional numerical model. In particular, penetration
of a simplified Cold Intermediate Layer (CIL) of the Black Sea into the Strait
specifıed at the boundary is simulated with the aim of testing the sensitivity
of the idealized model with respect to nudging strength. Successful penetration of a CIL-like
stratification can only be achieved by inflowing nudging time-scales less than
or equal to one day, while the outflowing nudging strength is found to be
insignificant. However, numerical instabilities at the boundary are observed
for strong nudging cases with tnudg ≤ 0.01 day suggesting
that a careful selection of the nudging time-scale is important to achieve
successful simulations of the CIL even in this highly idealized setup of the
Bosphorus strait. The presence of CIL altering the temperature distribution
within the northern section of the idealized channel has a significant impact
on the exchange through the strait. CIL reduces the density difference across
the strait resulting in decreased layer fluxes and velocities, while a
two-layer sense hydraulic control still holds at the sill.

Keywords

Bosphorus, Cold Intermediate Layer, Idealized 3d model

Üç boyutlu idealize bir İstanbul Boğazı hidrodinamik Modelinde Karadeniz Soğuk Ara Tabakası Zorlamasının Zaman Ölçeği Hassasiyeti

Abstract

İstanbul
Boğazı’nın hidrodinamiği üç boyutlu bir sayısal model marifetiyle idealize
koşullar altında incelenmiş, Karadeniz’in soğuk ara tabakasının (SAT) basitleştirilmiş
bir halinin idealize modelin kuzey sınırından penetrasyonu simule edilerek modelin
açık sınır koşullarıyla gerçekleştirilen sıcaklık profili zorlamasının zaman
ölçeğine (tnudg)  hassasiyeti
araştırılmıştır. SAT benzeri bir tabakanın boğaza pentrasyonu ancak bir günden
küçük tnudg (sınırdan içeri) değerleri ile mümkün olmuş ve sınır-dışarı tnudg
değerinin kuvvetinin önemsiz olduğu tespit edilmiştir. Bununla birlikte güçlü
zorlama değerleri altında (tnudg ≤ 0.01) kuzey açık sınırında sayısal düzensizlikler meydan gelmiştir, bu da
oldukça idealize edilmiş bir Boğaz modeli için bile SAT’ın başarılı
simülasyonlarını için zorlama zaman ölçeğinin dikkatlice seçilmesi gerektiğini
göstermektedir. İdealleştirilmiş kanalın kuzeyindeki sıcaklık dağılımını
değiştiren SAT’ın varlığı, iki tabakalı değişim akımı üzerinde önemli bir
etkiye sahiptir. Boğaz’ın kuzey kısmındaki stratifikasyonun değişimi ile
kanalın iki ucu arasındaki yoğunluk farkı, ve buna istinaden alt ve üst tabaka
akıları ve hızları azalmış olmakla birlikte, iki tabakalı yaklaşıma dayanan
kuzey eşiğindeki hidrolik kontrol kaybolmamıştır.

Keywords

İstanbul Boğazı, Soğuk Ara Tabaka, İdealize 3b Model

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