# Presentation: 449848

## Modification of Two Convective Schemes Used in the NCEP Eta Model

**More details in the **_**[conference paper](http://ams.confex.com/ams/84Annual/20WAF16NW/abstracts/73375.htm)**_
**Will deviate from paper to describe new Eta physics members in experimental SREF (21.3)**
**See also presentations by **_**[Manikin (4.3)](http://ams.confex.com/ams/84Annual/20WAF16NW/abstracts/73724.htm)**__**, **__**[Rogers ](http://ams.confex.com/ams/84Annual/20WAF16NW/abstracts/69239.htm)**__**[et al](http://ams.confex.com/ams/84Annual/20WAF16NW/abstracts/69239.htm)**__**[. (18.1)](http://ams.confex.com/ams/84Annual/20WAF16NW/abstracts/69239.htm)**__**, and **__**[Du ](http://ams.confex.com/ams/84Annual/20WAF16NW/abstracts/71107.htm)**__**[et al](http://ams.confex.com/ams/84Annual/20WAF16NW/abstracts/71107.htm)**__**[. (21.3)](http://ams.confex.com/ams/84Annual/20WAF16NW/abstracts/71107.htm)**_
**No “silver bullet” ******** yet to get *****improved***** *****Cu initiation***** *****and QPF***

**Brad Ferrier  (SAIC/GSO, NOAA/NWS/NCEP/EMC)**

## Expanded Physics Diversity

**Include greater physics diversity in SREFs to promote faster spread**
**Ops SREF ******** 5 Eta BMJ, 5 Eta KF, 5 RSM**
**New SREF ******** 2 Eta BMJ, 2 Eta KF, 2 Eta KFD, 2 Eta BMJsat, 2 Eta RAS, 1 Eta FSC, 2 RSM SAS, 2 RSM RAS**
**BMJ ******** **_**B**_**etts-**_**M**_**iller-**_**J**_**anjic**
**KF ******** **_**K**_**ain-**_**F**_**ritsch**
**** KFD ************ ***_***K***_***ain-***_***F***_***ritsch with full ***_***d***_***etrainment***
**** BMJsat ************ BMJ with “***_***sat***_***urated” moisture profiles***
**** FSC ************ ***_***F***_***errier ***_***S***_***hallow ***_***C***_***onvection***
**RAS ******** **_**R**_**elaxed **_**A**_**rakawa-**_**S**_**chubert**
**SAS ******** **_**S**_**implified **_**A**_**rakawa-**_**S**_**chubert**

## Expanded Physics Diversity (cont.)

**Create diversity within convective schemes by varying key tunable parameters**
**KFD ******** detrain all rain, snow calculated in KF Cu updrafts onto the grid-scale**
**All surface precipitation calculated from grid-scale microphysics**
**(With help from Jack Kain, there’s also a newer version of code that allows for partial detrainment of rain, snow onto grid)**

## Example of diversity within Cu schemes through parameter tuning

**0-36 h Rainfall (inches)**

## Motivation for Modifying BMJ

**Baldwin *****et al*****. (2002) analysis of BMJ => overactive shallow Cu, early triggering of deep Cu**
**SPC noted for years problems with BMJ adversely affecting pre-convective forecast soundings**
**“****Community” comments about early triggering of BMJ scheme, large areal coverage with weaker rain rates (RR), lack of horizontal structure, underprediction of heavier rainfall in QPF scores **
**Tendency for spin down of grid-scale clouds, precipitation during warm season**
**Some improvement with radiation “seeing” clouds in PBL & shallow Cu since July ’03 Eta implementation (see H.-S. Lin *****et al*****. poster P2.3)**

## Saturated BMJ profiles  (BMJsat)

**Saturated profiles w/r/t water (>-15C) to ice (<-40C)**
**Isobaric freezing of liquid to ice in parcel calculations  **
**Enthalpy conservation using Clausius-Clapeyron (DQ****sat****/Dt)**
**Latent heat of vaporization a function of temperature**
**New ********e**** tables w/r/t water (Bolton, 1980, JAS)**
**Increased heating, drying for column-averaged ascent**
**Added explicit triggering **
**	****P****LCL****-P****LFC**** ******** 50 mb; P-P****LCL**** ******** 25 mb in PBL**
**Parcel search in lower 1⁄2 of atmosphere (currently lowest 1/5)**

## Ferrier Shallow Convection (FSC)

**Behaves more like nonlocal mixing**
**Produces no surface precipitation**
**Adjusts convection to constant, cloud-averaged deficit saturation pressures (DSPs = p****LCL****-p)**
**Separate enthalpy conservation of Cp*T and Lv*Q**
**Avoids necessity of assuming moisture profiles**
**Includes cloud-top mixing (Betts & Miller, 1993)**
**10% or 20% of ambient air mixed at cloud top **
**Lifts each layer to check for instability starting from the height of the lowest condensation layer**
**Results comparing adjusted sounding profiles ****(modified Baldwin diagnostic software) **
**Much less active than BMJ, intended to provide SPC with improved pre-convective forecast soundings**

## 10-km Eta High Resolution Window Runs

**12Z 11 May 2002 10-km Central Nest runs**
**Strong spring storm, large-scale frontal organization**
**Large Day 1 QPF over prediction from E. Kansas to W. Illinois **
**Misplaced Day 2 QPF over upper Missouri Valley, lower Ohio Valley**
**18Z 24 April 2002 10-km Eastern Nest runs**
**Significant QPF underestimate in first 12 h by BMJ**
**Gradually dissipating convection along cold front, handled well by BMJ**
**QPF too high over Florida for KF, FSC runs**

## 0-24 h Precip (mm) valid 12Z 12 May 2002

## 24-48 h Precip (mm) valid 13Z 12 May 2002

## 24-48 h convective, grid-scale precipitation (mm)

## 24-48 h Cu, grid-scale, & total precip (mm)

## Impact of triggering on precipitation  structure

**(All fields valid 06Z 12 May 2002)**

**BMJ****(Z****top**** from highest EL)**

**BMJ**
**Trigger****Mod**
**(LFC within 50mb of LCL)**

## Characterizing Eta physics members based on subjective QPF assessments

## Characterizing Eta physics members (cont.)

**Cu triggering identified based on location of shallow (non-precipitating) and deep (precipitating) clouds****Convective cloud-top pressures ******** triggering**
**BMJ ******** large area of shallow Cu (well documented)**
**BMJsat ******** smaller area of deep Cu than BMJ **
**KF ******** smaller area of shallow Cu, but more shallow Cu in cold air north of fronts; shallow Cu seems deeper than other schemes (more “congestus”)**
**KFD ******** deep Cu tops are lower, but cover larger areas compared to KF**
**FSC ******** smaller area of shallow Cu than BMJsat; deep Cu tops (w/o sfc precip) can occur, but are rare**
**RAS********* ******** smallest area of Cu cloudiness, deep Cu dominates, dearth of shallow Cu (*********can trigger too early through capping inversions, less sensitive to CIN?)**

## 24-h fcst Cu cloud-top pressure (mb)valid at 12Z 12 May 2002

## 9-h fcst Cu cloud-top pressure (mb)valid at 21Z 12 May 2002 

## Cu triggering of Eta physics members 

## Positive attributes of Cu schemes

**BMJ works well in climatological conditions**
**Lower FAR (false alarm rate), better threat scores over the Eastern US in conditions of weak synoptic forcing**
**BMJsat works well in wet conditions, stronger forcing**
**KF preferred by forecasters out west**
**Triggers Cu in drier air masses with higher cloud bases**
**Better pre-convective forecast soundings over Central US**
**Full detrainment version reduces high QPF bias**
**RAS does well in large systems, strong forcing**
**Strength of quasi-equilibrium of convection with large-scale processes**

## “THE PHYSICS WHEEL OF PAIN”

## Modified KFD with Rupdraft function of WLAYER 36 h Cu Cloud-Top Pressure (left) & 24-48 h Precip (right)(Moral:  Sometimes too much structure is harmful)

**(back to Triggering of Convection )**