# Presentation: 436152

## 10.1  Implementation of a new grid-scale cloud and precipitation scheme in the NCEP Eta Model

**Brad S. Ferrier ****1****,****2****, Yi Jin ****1****,****2****, Ying Lin ****1****, Tom Black ****1****, ****Eric Rogers ****1****, and Geoff DiMego ****1**
**1 ****NOAA/NWS/NCEP/EMC, Camp Spring MD**
**2 ****SAIC/GSO, Beltsville, MD**
**Description of new scheme**
**Early results from CONUS winter 2001-2002**
**Future plans  ****(time permitting)**

***15******th****** Conf on Weather Analysis and Forecasting/15******th****** Conf on Numerical Weather Prediction***

## Motivation for new grid-scale scheme in Eta

**Rapid increase in grid resolution with time**
**Prior to Oct ’95  (80 km, 38 levels)****Oct ’95  (48 km, 38 levels)****Feb ’98  (32 km, 45 levels)****Sep ’00  (22 km, 50 levels)****Nov ’01  (12 km, 60 levels)**
**Limited computational resources for physics  ********  keep it efficient!!**

**Biases from forecasters of grid-scale precip starting too soon,  high bias in light precip areas**
**Development of spurious grid-scale precip maxima (“bulls eyes”) in 22-km run during summer of 2001; occurred often in 10-km testing**
**Complaints from NESDIS of overpredicting upper-level cloudiness**
**Update Eta to be more consistent w/ RUC microphysics**
**Spurious gravity-wave excitation due to episodic updates of T**

## Comparing grid-scale microphysics schemes

| FEATURE | OLD (Zhao & Carr) | NEW (NGCP01) |
| --- | --- | --- |
| Prognosticvariables | Water vapor, cloud condensate (water or ice) | Water vapor, total condensate (cloud water, rain, cloud ice, snow/graupel/sleet) |
| Condensationalgorithm | Sundqvist et al. (1989) | Asai (1965)[used in high res models] |
| Precip fluxesand storage | Top-down integration of precip, no storage, & instantaneous fallout.   | Precip partitioned between storage in grid box & fall out through bottom of box |
| Precip type | Rain, freezing rain, snow | Rain, freezing rain, snow/graupel/sleet (variable rime density for precip ice) |
| Mixed-phaseconditions | No coexistence of supercooled cloud water & ice, simple melting eqn.   | Mixed-phase at >-10C, includes riming, more sophisticated melting/freezing |

**Comparing grid-scale microphysics schemes**

******	****NGCP01**** – **_**N**_**CEP **_**G**_**rid-scale **_**C**_**loud and **_**P**_**recipitation scheme in 20**_**01**_

## Slide 4

## Precipitation Sedimentation

**(******** + ********k-1********V****K-1**** ******** ********t) ******** q****K****N***** = ************ q****K****N**** + P****K-1****N+1**

**(******** + ********K**** ********V****K ******** ********t) ******** q****K****N+1**** = (********K ******** V****K-1 ******** ********t) ******** q****K****N ****+ ****************PROD****K****N**

**(Note ****PROD****K****N ****is a function  of q****K****N*****)**

## Deriving hydrometeor species from total condensate

## From Ryan (1996)

**1****st****-guess size of precipitation ice (“snow”) as a function of temperature**

**N****o**** is the intercept, ******** is the slope, and [D] = ********-1**** is the mean diameter**

**[D] (mm)**

**N(D)=N****o****exp(-********D), **

**Observed size distributions of ice as functions of temperature, fit to (M-P) exponential spectra as**

**Adjust [D] so that  0.1L****-1**** ******** N****s**** ******** 20L****-1**

**HHHP (Washington state)****SMPC (California)****GM (California)****PLATT (multiple locations)****AWSE (Australia)****YL (China)****B, M (Europe)**

**1.0 **

**0.1**

**0.01**

**10.0 **

## Other features of NGCP01 scheme

**Algorithm discriminates between cloud ice and “snow” (precip ice)**
**No cloud ice if subsaturated (prevents too much sublimation)****or if T>0********C (melting) ******** only “snow” (precip ice) is present**
**N****s**** = 0.2****·N****i**** if at or above ice saturation T < -8********C, -3********C < T < 0********C****(N****i**** is number of cloud ice crystals, N****s**** is number of “snow”)**
**N****s**** = 0.1 ·N****i**** if at or above ice saturation **_**and**_** -8********C < T < -3********C**

**Variable rime density ******** assumes accreted liquid water fills holes of ice w/o changing volume ******** (Total growth)/(Depositional growth)**

**Efficient lookup tables store solutions for various moments (ventilation, accretion, mass, precipitation)**
**Composite of multiple velocity-diameter relationships**
**Increase in fall speed of rimed ice (B****ö****hm, 1989) **

## 12Z 3 May ’01 10-km Eta Central High Res Window Runs

**12Z 3 May ’01 10-km Eta Central High Res Window Runs**

**24-48h Total Precip 12Z 5/5/01 ****(Zhao)**

**(color fill – 24h precip  in mm,  contours of sfc pressure in mb)**

**24-48h Total Precip 12Z 5/5/01  ****(NGCP01)**

**24-48h Grid-scale  Precip 12Z 5/5/01 ****(Zhao)**

**24h RFC Precip 12Z 5/5/01 ****(Observed)**

**Precip****blow up**

## Reduced high bias in light precipitation (areas 1, 2) and improved orographic precipitation (area 3)

**(0-60 h forecasts of accumulated precipitation in inches valid 12Z 28 Oct 2001)**

## 22-km Eta (Zhao)

***Courtesy of COMET***

**22-km Eta (Zhao)**

**12-km Eta (NGCP01)**

**24h Gage Analysis**

**24h precip valid 12Z 14 Nov 2001**

**22-km Eta (Zhao)**

**12-km Eta (NGCP01)**

**24h Multisensor**

**24h precip valid 12Z 20 Oct 2001**

**More examples of NGCP01 reducing high bias in light precipitation**

## Reduced High Bias inUpper-Level Cloudiness

**Reduced High Bias in****Upper-Level Cloudiness**

**Observed (upper right) vs.**
**forecast (bottom) cloud-top**
**pressures (mb) for 12Z on 28****February 2001**

## OLD version(Zhao, periodic T updates)

**OLD version****(Zhao, periodic T updates)**

**NEW version****(NGCP01, continuous T updates)**

**Removing spurious gravity wave excitation through****continuous, incremental T changes by cloud processes (Cu & Grid)**

**Vertical motion valid at 00Z 5 May 2001 from 10-km Eta Central**

## Operational Eta Implementation on 27 November 2001

**Increase in resolution from 22 km / 50 levels to 12 km / 60 levels**
**Changes in Eta 3DVAR analysis to follow Global SSI procedures**
**Refined bias correction for all radiances**
**Use of NOAA-16 radiances**
**5 more channels for NOAA-15 & NOAA-15****(mostly AMSU-B moisture channels)**
**Radiance thinning based on cloudiness **
**New grid-scale cloud microphysics scheme (NGCP01)**
**Changes in observed precipitation assimilation Eta Data Assimilation ****System (EDAS) to be compatible with NGCP01**

## Monthly Equitable Threat Scores (24h, 36h, & 48h forecasts)

**Monthly Equitable Threat Scores (24h, 36h, & 48h forecasts)**

## Apr ‘02

**Threshold (inches)**

**Threshold (inches)**

**Equitable Threat Score**

**Apr ‘02**

**May ‘02**

**Eta**

**AVN**

**NGM**

**Eta**

**AVN**

**NGM**

**Threshold (inches)**

**Threshold (inches)**

**Equitable Threat Score**

**June ‘02**

**July ‘02**

**Eta**

**AVN**

**NGM**

**Eta**

**AVN**

**NGM**

**Monthly Equitable Threat Scores (24h, 36h, & 48h forecasts)**

## Dec ‘01

**Threshold (inches)**

**Threshold (inches)**

**Bias**

**Dec ‘01**

**Feb ‘02**

**Eta**

**AVN**

**NGM**

**Eta**

**AVN**

**NGM**

**Threshold (inches)**

**Threshold (inches)**

**Apr ‘02**

**June ‘02**

**Eta**

**AVN**

**NGM**

**Eta**

**AVN**

**NGM**

**Monthly Precipitation Bias Scores (24h, 36h, & 48h forecasts)**

**Bias**

## Two Examples of Excellent Eta Performance

**Winter 2001-2002 over the Pacific Northwest Coast**

## Summary of Physics Changes for Fall 2002

** ****EDAS**
**Improved optical properties of convective clouds (Slingo, 1987) in precipitation assimilation**
**(Other EDAS changes, including 88D radial winds)**

** ****Grid-scale cloud microphysics**
**Corrected minor bug in ice nucleation rates, ****probabilistic freezing of supercooled rain**
**Cycling of all new features of NGCP01 scheme (preserves various ****hydrometeor species between model cycles)**

** ****Radiation**
**Longwave called hourly along with shortwave**
**Modified optical properties of shallow Cu (assume 10% cover)**
**Cloud fraction increased by 20% for deep convection**
**Xu and Randall (1996) for grid-scale cloud fraction (minor mods)**
**Changed absorption coefficients to be more consistent w/ model clouds**
**Removed legacy code that, on occasions, set cloud fraction to****zero for clouds in the lowest 100 mb and in the upper troposphere**

## Expected Impact of Fall 2002 Changes

** ****Slight improvement in fits of T, RH, Z, and winds w/r/t RAOBs**

**Slight improvement in 2-m T and RH fields, (very) slight degradation****in 2-m winds**

## Future Research

**Currently testing modifications to BMJ convective scheme **
**Source of cloud-base air**
**Calculating cloud tops for deep and shallow Cu**
**Upward heat and moisture transports for deeper, nonprecipitating ****convection (congestus)**
**Make moisture profiles much more moist, enhance grid-scale cloud ****processes and interactions with convection**

**Major upgrade to short- and longwave radiation**
**Follow lead of Global Model development (Y.-T. Hou)**
**Cloud shortwave optical properties (Chou *****et al*****., 1998)**
**AER RRTM ****(Rapid Radiative Transfer Model)**** IR (Mlawer *****et al*****., 1997) **
**Surface albedos for direct and indirect radiation**