<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Hi,<div class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Dec 26, 2019, at 2:13 AM, JIATONG <<a href="mailto:jiatong@radi.ac.cn" class="">jiatong@radi.ac.cn</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div style="caret-color: rgb(0, 0, 0); font-family: SFMono-Regular; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span class=""> And here is my question. </span><span class="" style="font-size: 10.5pt; line-height: 1.5;">I am trying to model nonliear internal waves with two open boundaries </span><span class="" style="font-size: 10.5pt; line-height: 1.5;">without free surface (rigid lid) in 2D </span><span class=""></span></div><div style="caret-color: rgb(0, 0, 0); font-family: SFMono-Regular; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="font-size: 10.5pt; line-height: 1.5; background-color: rgba(0, 0, 0, 0);" class="">in </span><span style="background-color: rgba(0, 0, 0, 0);" class="">nonHydrostatic<span style="font-size: 10.5pt; line-height: 1.5;" class="">. </span></span><span style="font-size: 10.5pt; line-height: 1.5; background-color: rgba(0, 0, 0, 0);" class="">In the model setup, I input the b</span><span style="font-size: 10.5pt; line-height: 1.5; background-color: transparent;" class="">arotropic tide at west and east boundaries over the bottom topography, and want the </span></div><div style="caret-color: rgb(0, 0, 0); font-family: SFMono-Regular; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="font-size: 10.5pt; line-height: 1.5; background-color: rgba(0, 0, 0, 0);" class="">barotropic tide can </span><span style="font-size: 10.5pt; line-height: 1.5; background-color: transparent;" class="">evolve into nonlinear internal wave(internal solitary wave). dx is set to 50m and dz is set to 5m. dt is 5s. However, </span></div><div style="caret-color: rgb(0, 0, 0); font-family: SFMono-Regular; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="font-size: 10.5pt; line-height: 1.5; background-color: transparent;" class="">the T of the model output is filled with </span><span style="font-size: 10.5pt; line-height: 1.5; orphans: 2; widows: 2; background-color: transparent;" class="">noises </span><span style="font-size: 10.5pt; line-height: 1.5; orphans: 2; widows: 2; background-color: transparent;" class="">and I can not identify the wave signal(its lenght scale is about several hundred meters). </span></div><div style="caret-color: rgb(0, 0, 0); font-family: SFMono-Regular; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="font-size: 10.5pt; line-height: 1.5; background-color: rgba(0, 0, 0, 0);" class="">I've tried to set various dx, dz and dt steps, but </span><span style="font-size: 10.5pt; line-height: 1.5; background-color: rgba(0, 0, 0, 0);" class="">without positive<span class="Apple-converted-space"> </span></span><span style="font-size: 10.5pt; line-height: 1.5; background-color: rgba(0, 0, 0, 0);" class="">result. And I also tried the </span><span style="font-size: 10.5pt; line-height: 1.5; background-color: transparent;" class="">Laplacian viscosity coefficient changing </span></div><div style="caret-color: rgb(0, 0, 0); font-family: SFMono-Regular; font-size: 14px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""><span style="font-size: 10.5pt; line-height: 1.5; background-color: transparent;" class="">from 1e-5 to 1e-1, some very small noise have been </span><span style="font-size: 10.5pt; line-height: 1.5; background-color: transparent;" class="">removed, but </span><span style="font-size: 10.5pt; line-height: 1.5; background-color: transparent;" class="">there are still some large noises. </span></div></div></blockquote><div><br class=""></div><div><br class=""></div><div>What do you mean by “large noises”? The model results you are plotting look reasonable to me if your forcing is moderately strong. You would expect a lot of turbulence near the generation site. </div><div><br class=""></div><div>If you are worried about grid-scale noise, you can often lessen that by changing to a higher-order advection scheme, at the risk of introducing more numerical dissipation and diffusivity: <a href="https://mitgcm.readthedocs.io/en/latest/algorithm/algorithm.html#advection-schemes" class="">https://mitgcm.readthedocs.io/en/latest/algorithm/algorithm.html#advection-schemes</a> But the real advnatage of that is increasing the time step, not particularly to make the results look better. </div><div><br class=""></div><div>Cheers, Jody</div><div><br class=""></div><blockquote type="cite" class=""><div class=""></div></blockquote></div><br class=""></div></body></html>