<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;">Are you trying to add mass at the surface only, or throughout the water column? If at the surface only, you can use “realfreshwater” mode and prescribe evaporation and precipitation instead, which would take care of adding mass correctly. To avoid impact of evaporation and precipitation on salinity, you could set salinity of your domain to zero.<div><div><br><blockquote type="cite"><div>On Apr 2, 2025, at 11:05 PM, 赖六娃 <yhlai@pku.edu.cn> wrote:</div><br class="Apple-interchange-newline"><div><meta charset="UTF-8"><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant-caps: normal; font-weight: 400; 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; font-size: 14px;">Dear MITgcm-ers,</span><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; 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;"><span style="font-size: 14px;"><br></span><div><span style="font-size: 14px;">I’m trying to include a mass-loading forcing in ocean circulation simulations.</span></div><div><span style="font-size: 14px;">The 3D distribution of Evaporation/Condensation rate E in kg/m2/s is known. I’m testing its influence on ocean circulation.</span></div><div><span style="font-size: 14px;">Note that I only want to consider the Evaporation effect on mass loss and gain, and not consider its influence on salinity.</span></div><div><span style="font-size: 14px;">So, in my model setup, I multiply E*dx*dy to make it in unit of kg/s.</span></div><div><span style="font-size: 14px;">I set: addMassFile='addmass_160x72x44.bin’, and also <span style="color: rgb(64, 64, 64); font-family: Lato, proxima-nova, "Helvetica Neue", Arial, sans-serif; font-variant-ligatures: normal; orphans: 2; widows: 2; background-color: rgb(252, 252, 252); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">#define </span><a class="reference external" href="http://lxr.mitgcm.org/lxr2/ident/MITgcm?_i=ALLOW_ADDFLUID" style="box-sizing: border-box; color: rgb(48, 145, 209); text-decoration: none; cursor: pointer; outline: 0px; overflow-wrap: anywhere; font-family: Lato, proxima-nova, "Helvetica Neue", Arial, sans-serif; font-variant-ligatures: normal; orphans: 2; widows: 2; background-color: rgb(252, 252, 252);">ALLOW_ADDFLUID</a> in code/.</span></div></div><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; 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;"><span style="font-size: 14px;">However, I did not see its influence on circulation, I’m not sure if I set correctly.</span></div><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; 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;"><span style="font-size: 14px;">And let me make sure that negative addmass means mass source, and vice versa?</span></div><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; 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;"><span style="font-size: 14px;"><br></span></div><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; 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;"><span style="font-size: 14px;">Best regards,</span></div><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; 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;"><span style="font-size: 14px;"><br></span></div><div style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; 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;"><span style="font-size: 14px;">Yanhong</span></div><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: 400; 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; float: none; display: inline !important;"></span><br class="Apple-interchange-newline"></div></blockquote></div><br></div></body></html>